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THE

CB PLL
DATA BOOK
Lou Franklin
.hA

Pr

P2 P3 P4 Ps P6

T/B

GND

V""

A Repair& ModificationReference
IncludesAmerican,British,& EuropeanCB Badios
AM, FM, & SSB Circuits

CONTENTS

tbv
ther
nted
)rseility

INTRODUCTION ....
.......... I
Section I - BASIC PLL BACKGROUND .
...... s
Frequency Mixing - Intermediate Frequencies - SSB Mixing - The
"Odd"
British Channels * The PLL for FM Use - A Basic Crystal
Synthesizer - Equivalent PLL Synthesizer - Elements ofThe PLL System
- Reference Oscillator & Divider - Programmabìe Divider - phase
Detector - Loop Or Low,Pass Filter - Voltage-ControlledOsciìlator - The
Loop Mixer - The 5.12 MHz Loop Mixing Output - Current Technical
Trends - Special Chip Functions - The T/R Shift Misprogram Code Pin - Frequency SelectPin - Automatic Ch. g,/Ch. 19
Command - Scanning Interface
Section II - BACKGROUND FOR MODIFICATION METHODS .......
Typical Synthesizer Circuit - Binary Programming - VCO Circuit -Loop
Mixing - Phase DetectorCorrection - ReceiverIFs - Transmitter Section
- Truth Charts - BCD Programming - PresettableDividers -Multimode
Programming - Controlling Program Pins - ROM Code Converters Other ROM Variations - Loop Mixer Modifications - CB-to-Ham
ConversionProblems- Sample Modification - Crystal Switching Methods
- External Crystaì Oscilìators - Crystaì Sources - The
ReferenceOscillator Crystal - The Impossibìe Chips

32

Section III - PLL CHIP SPECIFICATIONS
Inside The Mysterious PLL Chip - Explanation of pin Functions - N.Codes
of NewerROM Chips

6l

Block Mixing Diagrams (Pages 6?-92);

Uniden "Export" SSB- SharpCB5470- LC7ll3 SSB- LC7l30/31/3b
-LC7131 SSB- LC7136l37- MC8719SSB- NDI Early - NDI t are
-PLLO2A AM 3-Crystaì- PLLO2AAM 2-Crystal- PLI,O2ASSB PLLOSA/O8A- REC86345_ SM51O4SSB _ TC5O8O/81
SSB _
- TC9109/M88733/LC7r32/CSI2r
- uPD858AM 2-Crysrat
TC9106/9119
- uPD858AM 3-Crystal- uPD858SSB- uPD861AM ROM - uPD861
AM Binary- uPD2814/28r6/LC7120
AM - uPD2816
SSB- uPD2824
SSB
Pin Functions t(Pages93-107):

c5121- CCIil001- CCI3002_ HD42851_LC7rr} _LC71:.3_rc7v0
- LC7130
/ 3r/ 35/36/ 37_ M58472_ M58473_ MB87r9/ 8734_ MC145106
- MC14568/14526
- MM55108
_ MSC42502
_ MSM5807_ MSM5907
-NDC4OO13- NIS7261A_ NIS7264B_ PLLO2A _ PLLO1A_ SM5104_ SM510?_ SM5118_ TC5080_
PLL03A/08A- REC86345
- TC9109/MB87SB
TC9102 TC9103- TC9106/9119
- upD858_
- uPD2812
- uPD2814
- uPD2816- upD2824
uPD861- uPD2810
LATEADDITIONS:LC7132,
SM5123A,
SM5124A
. . . . . . . . . lo8
L A T EA D D I T I O NC: P IC h a s s iBsì o c M
k i x i n gD i a g r a m. . .
.......... l0g

INTRODUCTION
The Phase-Locked-Loopor "PLL" Frequency Synthesizer used in CB
radios is a marvelous device. It can generate all the signals neededto
run a complex transceiver, is more accurate than crystal control, and
more reliable becausefewer parts are needed.However, understanding
its operation seemsto causea lot of anxiety among CB operators as well
as professionaltechnicians.It's the purposeof this book to explain in
the simplest, most non-technical terms possible how the PLL works.
Anybody interested in the technical side ofCB radio should find it quite
heÌpful. I've tried to write this for both the casual CB hobbyist and the
professional serviceman.
CB radio is now a worldwide hobby. As an American who's seen it
change from vacuum tubes to transistors, from crystal synthesizers to
PLL synthesizers, I'm in a unique position to explain the PLL's
"chips" detailed here are
evolution. While many of the circuits and IC
actually obsolete now, there are still a lot of those radios out there
needing repair! And since most countries have limited CB operation t<r
only 18,22, or 40 channels, a lot ofinterest these days is in knowin$ how
"legal" channels or
to expand a CR rig to cover more than the
frequencies. Many of the older rigs are actually much better for this
purpose. There is also a lot of interest among ham radio operators in
converting the CB into a 10-MeterHam rig. I will explain in these pages
how PLL repairs and modifications are approached.In many casesthe
changes are quite simple; it's no accident that a lot of American and
European transceivers using certain PLL circuits are so popular even
today. On the other hand, you may be very disappointed to find out that
the most recent generation of IC chips for U.S., U.K., and European CBs
were designed to be aÌmost completely non-modifiable. Better keep that
older rig if you have one!

BRIEF
HISTORY
& OEVELÍ]PMEI{T
The main reason for the development of PLL synthesizers was the
American CB service expansion from 23 to 40 channels in 1976.Until
"crystal
then CBs used a method of frequency generation called
synthesis" or "crystal-plexing". By electronically combining the
"mixer", all the
signals of 2 or 3 quartz crystal oscillators in a common
various Receive/Transmit signals (which are normally not the same)
could be created with only 12 or 14 crystals for AM and a few more for
SSB. This was a great savings in cost, circuit complexity and space,
becauseotherwise at least 46 different quartz crystals would be needed,
- 1 -

one pair per channel.
enough.quar tz left inthe world to
give it aìl to the CB manufacturers;
^T.ffj:.yasn,t
they hid io ,".rr" "o_" for all those
Seiko wristwatches!
With CB interest erowing very
rapidly. new methods were required
becauseof the incréased numbe,
oii"grr "rtà"""1s. Manufacturers had

out trowto generat"u t".gà rri_tlri?"ig.ruf.
lor{r^s.1ie
*ith a minimum
o
r parts,space,comolexity,.and of1o"";;,
;";: iÈ" ;;;;;;;;.;i,
#L.t
timò.the a-*r."]
rcC.r,rrou.,""d
Ì{l!!"ti'.gT,
Pv-l.t'ò
"digital"
irs
cB expansron,
electronic_svn*t".ir"i"'*é"rr."av'*"riil;;.i;
tasr.senerarionor zs"_"'[;";;i'ù.3:";r,pment
i1:l
f: to usepLL
had alreadv
Degun
techniques
ratherthan crv.iir". rrr"r" il;;i;;tt:
were very compricated
b.ecause
tttuv ,"qulrid as many as g discrete
lntegrated

Circuit (lC)
"hip; A'.,;';;re
and more electronic
-silicon
tunctlons were crammed.into
a imaller chip space. Today,s pLL
can perform all the needed-i;;;;"
lTÌ.î""T
of channel selection
ano
stgnal generation,

using
, .l"gi" LSi (ì;L;'rg"il;#i;:
tegration")deviceanda ttanarit-only
oÉt"r"ui?i.t.. es we,, see,this fact
r
i_r!?rh blessinganda curse:G".à b";;;;Ì;J

keeps_
radiopricesafford
abi",;; ; ;;; il:;" i:fi i:Tili fH,jr","X?î

modifications even harcferl

The FCC and other authorities
quickly found that because
of the
unexpectedpopularir.yof

C1,.wfth'Àiiiil;;l;"pte
ail competingfor
the samechannels,the use.ofilf egaiÀìà
l""rlttori""a
frequencies
was
becomingthe rule rather than À;;ó;t""
.rìa,rri.
is
basicalÌy
rhe
situationtodav'Technici,ans
soondi."ou"rJthàt the first generations
of PLL rigs weresimnreto modifv.
Th;'Fc''c;ffi changedits ruresto
CB man_ufaciu.,"T u." "p""lrl-ÈLl
::luir: Australia,
chips to prevent this.
1o
$rnce
Holland,_B.it"i",
a"'a-oih",
ólrrni".
had legalizedCB
1.9'ng
after the U.S., their governments
took
the
hint
and started off
orrectly with the -or" .""ù." "hi;;i;;it"'iro*".,r",
through
various
legattoophotes,cerrain-,r!"i;J;;à"i,
"rò"ril in the U.S. and other
countriesare still allowedto be impóitJ;i;"th"
..good,,pLL
chips,
and this subjectwill be coveredi;
;:;;;;;;;iii;;""
In all fairness I should mention th_at
someinterestingfeaturesnorround the newestchips are capableof
in
automaticcommandof the Ct r"""iS earìi"r'sl;"rrtio.rs. For example.
Éili*à""" Ci,r""el or Channel
19 Road InformationChannel,.scan.rirrg,,i"Àó.v,
keyboardcontrol,
sreater reliabilirv. ete. This.is,!"ri.;iiy. ;h;;;?e
state-of_the_art
in
PLr t echnotosv is todav,.and rh"r;
i;iil;l;
-ì.à
ir,.,
eouernmentscan
oo to preventany determin^ed
radio
fi;
rearrywants to' I think it's safeto hobbyisfl;;*úifyi;;;;rc
assu-mé
that
iniormation
in
this
book
oeLarlrngoperationof the latest pLL
d""l;;. ;ìlTLe accuratefor rnanv
years to come.And since there
"r" ,tiìi.ifìio""
"f "f a* ,ig" ;;ì A;;?

ne(
rig

B0
I

'v

) ^^

thr
chr
wa
ser
ele
in fr
be
st tI

s-v
ctc
't'hi

t-..-

not
Ìnt(
to

SON

tha

s0n

'f

he
d iff
Chr
osc
suc

The
and
imp

eno
e vtrt

the
u sir
chip
typi
chip
spe
SA1

the world to
rfor all those

ere required
acturers had
raminimum
was the PLL
I its CB exell along. In
had already
first circuits
ts 9 discrete
re electronic
oday's PLL
rel selection
ge-Scale-Insee,this fact
iability and
bugs make

ause of the
mpeting for
uencieswas
asically the
3enerations
I its rules to
revent this.
egalizedCB
started off
rgh various
J.and other
PLL chips,

r capableof
or example,
cr Channel
ud control,
'f-the-art in
lments can
garigifhe
.nthis book
lefor many
:sout there

needing maintenance, the amount of attention devoted to these older
rigs is justified.

B00K
0RGAt{tzATt0il
I've divided this book into three general sections. The first section
describes basic PLL theory in "building block" form. We'll start with
the simplest chips and proceed to the most complex, in
chronological order becausethat's the way they have evolved. In this
way, you'll begin to understand how the various IC changes affcct
servicing and modification. I'll assume that you have very littlt'
electronic knowledge, even though some of you may be very wellinformed about other areas of CB electronics.The PLL circuits will only'
be illustrated in "bìack box" or block diagram form to keep things reall)'
simple. For example, a transistor switching circuit will be representecl
symbolically as a simple switch. Components like resistors, capacitors,
etc. will rarely be shown at all unless very essential to the discussion.
This way you'll never have to worry that you've gotten in over your
head! Specific radio theory regarding AM, FM, or SSB communication s
not directly related to the PLL are left up to you for further study if
interested. Some very basic radio theory must be included, but I've tried
to keep it very uncomplicated. Since I want everybody to learn
something about this subject, some areas are oversimplified, and I ask
that you professional technicians out there have a little patience if
something seemsobvious to you.
The second section deals with modification methods as they apply ttr
different generations of PLLs. We'll be discussing such things as Truth
Charts, programming in binary, BCD and ROM, Loop Mixers, external
oscillators, and tips on how to attack the various types ofPLL circuits
successfully.
The last section shows technical specsand block diagrams ofthe chips
and circuits themselves. I've included every known chip of anv
importance. (There were a few very old chips that never lasted long
enough to bother discussing.) To my knowledge this is the only book
ever published devoted entirely to the subject of CB PLLs. Along with
the chip pin diagrams is included a list of every radio make and model
using that chip which was known at press time. Since several groups of
chips work the same way, I've also included sample Truth Charts
typical of such groups. I've tried to include special notations when a
chip contains some unusual feature you should know about. All the
specific pin functions were gathered from manufacturers' spec sheets,
SAMS Fotofacts and other service manuals, and personal experience,

-3-

-

and are accurateto the bestof my knowledge.
If you don't find vour oarticular.rig moder
incrudedhere,chancesare
that it's identicalio ",,-. ott.. ris,".;;;h;;;;."
basically now three
Far E asr.companie-s(Cybernà;,ú';i.il;;iiu*on)
that m ake gg%,
of

the world'sCB radiosanyway.O"; p-il;;È

.h;;;ì;-;;
#;;i.i
under dozensof brand namesas most óf youairàaay
know.
F.orcertain
well-known

chassis,
I've incluied';ffiit; pt';oard numbersso
that
youmightpossiblyidentifyu" u"t-íu"*ii*in
,t ur number.
to Englandandtrìurope
in l9g1to srudytheCBsituation
Yl_r^*'o^Llto:
tnerehelped
gathering

crqa-tlyin
tÉ.especiuicircuit ínio.rn.att;; f;;;
tn";. pages.M_ost
Americans
will never.;th" ,;;;;;;;;;;1.,;ì
lltherr tavorire
radios:informationun ti,ÀuJàiiionoi!nà*,"r"i'0:i;ó
channelsand FM shouldhelpyour o*"
-oain"ution attemptswhen
y ou seeh ow th ey're don^e
com'nier.i.ll;. ì;i;;;ti
;; ;; ;ir;'ií;il;;;
versions
of popularAmericanrigs,as wellas thenewest
,.legal,.
U.K._
FM rigs' arrivàdiustin time r" "'il;;;iliJ
foor,
.o
that
rhis
is
trulv
an i n ternarionalreferenrewgtlj'Éi
:;;o'oii{
"iiòi.'srp.r.tar
rh;;;;;il
;;;;;;".
;i'
rigsIike^rhe
c^obra

r48GTi-tx.,Fi ri,nrì
86003900.
Galaxv2t00superGaraxv.
andRangà;
ÀirGoo
fiàJ".i*J ií",,"rr""
U.S.,andareincjuded
in $òti; ilI.^ifi/iÉrliir,"_rrics
onmosrof
theseif you

needone.)In.addiiiun,'i;;B;ri;îCÈ
overto theAmericanF(:('channir-".rer;."i'so sysremhaschaneed
UK radiosarenow
usingthe AmericanpLL cnrpsanyway.
Obviously it's verv difficult (and expensive!)
to contrnuously update a
boo-klike this as new modeis.^p;";;,-b;;;t"
ù-uri" information f.r
understanding any plL circuit yàu'll .u".
*" """ be found here. I,ve
personally managed to. careìog literally
iÀ".r""a"
of makes and
models,over

manyyearsby the u-se
"f SAi4S-i..t;fu"t., i;"1;;;;;.;i;;

manuals, and schematicssent tome by -y ,"ra"... ,_
f
"f *rv."u.*iorà
to add new radio models to my files f-;;i;ù
furure revisions and to
help my readersidentifv a specific"hu..i,
,,. itii circuit. photocopies
of rig circuit- diagrams u." ,lrvuy.--uop.""lràa.
I weìcome your
commentsand suggestionsand frupétt is
UooLhelps yt,u.
Good luck in the Battle Of The pLLl

Lou Franklin, K6NH
"Supersparks"

P h o e ni x , A r i z o n a U
, .S.A.

-4-

, chancesare
ìly now three
make99%of
may be sold
v.l'or certain
rbersso that
rber.
CB situation
nation found
f" modelsof
Lother80-120
empts when
heEuropean
'legal"
U.K.Ithis is truÌy
s of "export"
r 3600/3900,
rived in the
s on most of
ras changed
lios arenow
rly updatea
rmation for
rd here.I've
makes and
tory service
aysanxtous
rionsand to
?hotocopies
lcome 5,clur

o n aU
, .S.A.

SECTION I
BASIC PLL BACKGROUND

FBEOUEIICY
MIXIIIG
This principle is so basic to radio theory, whether AM, FM, or SSB, that
it must be discussed briefly before proceeding further. The reason is
becausemixing or "conversion" is a processthat requires two or more
signals, and if there are no longer any crystals used to provide such
signaìs, we have to find them somewhere!And that "somewhere" is in
the PLL circuit.
Whenever two signaÌs are mixed together electronically, the result is
two new frequenciesin addition to the originals. These new frequencies
are nothing more than the sum and difference of the original two, as
seenin Figure 1. In this example,by mixing a 10 MHz and a 15 MHz
signaÌ together,the result will be 10 MHz, 15 MHz, SMHz (15 MHz - 10
MHz) and 25 MHz (15 MHz + 10 MHz). By then passing the signals
through a selectively tuned circuit, only one of the mixing products will
remain and the other will be rejected.The mixing processis important
in PLL circuits becauseit provides other signals required to operate the
radio that have nothing to do with the actual channel generation. Of
course these other signals could be generated by individual crystai
oscillators or tuneable oscillators, but this adds cost and complexity to
the radio. The first generations of PLL circuits did use up to 6 individual
crystal oscillators but they've now evolved to the point where a singÌe
70.240MHz crystal is all that's needed,at least for AM or FM.

FIGURE 1, BASIC SIGNAL MIXING PROCESS

-5-

the mix in_gprocess_1o
t
The reason is becausemost of
.Y
! si.i s n a l s
the
n e e d e di n a 2 7 ._iaportant?
MHz CB;is;;;';"
difficult to process
directly and economic"'y *hii;ì;ii;s
ff;;;*
good performance.
The CB/10M Ham band is considered"a
.utfr". frìgf, frequency, and it,s
much better to convert a27 MHz,ls""l
ào*;to'9o-_" lower frequency
where the various Receive_,2Tr"""rni
"lr"uit" *o"r, t o" "o touchy. you,ve
probably seen the terms,,Single-";;;;;r;;;''
;; .,Doubte_conversion,,
applied to receivers;this m.eans
that the ZiùHz signaÌ is ,,converted,,,
"mixed",
or ,,heterodvn"a" ao-"-o.r"";;;;;
to a iower frequency
that's easierto pr.t,cess.
A_typicalAM ;. FMó;rig
"dual-con
-"o-.r,ru."ro.,
is generalÌy of the
versit,n" 6uo". For SSB, u .i.rgl"
is all that,s
neededbut since theie are nu Ce.ig"
l,;;i;;;;ìy
"us"
SSB
capability, the
majority crfmultimode tranr"uirr"..
dr.f8."""."i"
n
forAM and FM
onty. with the SSB circuirs.r.i;;
;;ì;;rì;;i;
"o,.,r"rsron.
(Sinele_
crnversion quire

is
acceptabte
r* ssÉ il;;l;,h"
C;R';i;;;i;,"r;:
passedthrougha verv sharp.crysral
filter,
tvpi""ffl
"ri;;;;%MH;,
10.G9b
MHz, or rr.275lvrur.feî"ìlìlrì'*;".',!1_,u,"
up or down and
passihgthem throush sharply-tuned
circuiis,iil" _u"h easierto get
o_":,fo.Tance,
eJoeciattii; ;;-";;.:i;J
_"." runed
:^ _:-1
more.selectivity
and sensitivityduring ."""ftiu.r, ."j circuits,the
ìh;;;;;
reduction
of unwanted,,spurious':
.ig"ìi.'a"ri! transmission.

ilTERME0tATE
FnE0uEilctEs
ftFl
lhe resuìt of converting a 27 WHz

signaì down to a lower frequencv
duringreceprirn
is an ,.interm"dtrt"iifi;;;;;
;; ùi:;. iHH;:::

often th.e only I I.', as shown in Figure
Z'-a.Érv"rr". when a double
conversionoccurs,the resu.ltis two
IFs. tt """ u.u called the ,.first,,or
"high"
II,' and the ,,second""J ,:lgrr;f n f,i*ùl
r_o For CB use,these
two IF frequencies are almost .,rrir,"..riÌy
iO.AósrrAffr, and 4Sb KHz.
This is partlv becaus".*"I" was
already . loi uf existing electronic
equipment using theseIFs long t"f"."
òÍ."df.
"r_" along. (Eg, AM
and F M broadcast receivers,portabres,
"rro.t*àì"
recelvers,scanners.
'fhus
aut' radios,

etc.)
p;;;. ;;';ri".ai""à,rriìT
yreeded
{t-re,

manufacturers,
provenreliaur",
u"a "fr"àp.A.rith".."u"onis because
a

very clever use of the pLL c-ir"uit,
*frl"f,ll;l-;";
always based upon a
10.240 MHz Master Oscillator,
"u; ù; _.àì ," provide these IF
"injection"
signaÌs. When rhe i"j"";i;;s;iii",
utou"
it's called "high-side" injection, and io*'-rììJ;r":ection rhe CB signal,
is when it,s
below the 27 MHz cB signal. otder ptLs
u"la u"tr, methods but the
very newest chips use low-sideinjection
for reasons you,ll see later.
-6-

causemost of
rlt to process
performance.
Lency,and it's
verfrequency
ruchy.You've
t-conversion"
"converted",

FIG T]RN 2. FREQ UE N (: Y CONV F:RS/ON PROC'ESS

A . S i n g l eC o n v e r s i o n

,rerfrequency
neraÌly of the
is all that's
apability,the
r AM and FM
sion. (SingleI signals are
rear7.8MHz,
or down and
easier to get
d circuits,the
nd the more
.ission.

'er frequency
This stage is
hen a double
lhe "first " or
lB use,these
rnd 455 KHz.
ng electronic
ong.(Eg,AM
)rs,scanners,
availabie to
n is becausea
basedupon a
ide these IF
re CB signaÌ,
r is when it's
;hodsbut the
u'll seelater.

I n l e r m e d i a l eF r e q u e n c y( l F )
CON VERT ER

o u t o u t t o D e t e c t o r& A u d i o A m p s

B . D o u b l eC o n v e r s i o n

27 MHz in

1sl or High lF

2nd or Low lF outDut
lo Detector & Audio
Amps

-7 -

S_everalverypopular CB chassistypes use only a single
IF of T.gMHz.
(Eg,

Cobra r40/.42GTL or Supersìarl;60wiíh MBé719pif,,
itiil
"Adams"

138,/139xLR or President
with 858 pLL.) In doing this,
recerverperformance was cheapenedanclselectivity worsened.
f-he faci
that these particular chassis are stilÌ e"tremely popular
t"J;;- i;
becausethey are very easy to modify, not becauseoftheir great
receiver
performancel A deluxe version of the Mtsg7l9
chassis (Eg, Cobra
148/ 2000G"rL.new President "Madison" and ',Grant',1 "rr"."li"t
,"lv
an. easy modification, but here the manufacturerstook
the troubre o"f
using dual conversionon AM with a stancìard4b5 KHz
IF. They also
charged you more for this feature. separate fiìters coulcìbe
usecrfor each
mode to increaseselectivity,becausean SSB signal only requ
in,s ab<,,ut
half the bandwidth of AM or FM. Where in the iirst^"ru_;i;;
compromisedIF filter bandwidth is usedwhich is basicaily
to, *ià" for
SSB and too narrow for AM,zFM, in the ,,de.luxe,,cha-.ssisyuu g"i
gl":ll"-"-t_la"ctivity in every mode. The use of separate SSe ;à
AM/FM IFs is also found in all American ,.rd Eu.opur.,
,r".oiu.r. o]
rigsusing the verv popular pr,L0 2Aprl, chip. This
sÀort background
on design trade-offs will help your ,.,ncle"stanclingof plt,
iiil;
circuits to be described later.
SS8MIXII{G
Some unique problemsoccurwith pLL or crystal rigs in the
SSB mode.
With AM and FM rigs, all we need to do is to generate(or
receive)a
carrier signal and then modulate (or clemodulatl)it. However
for SSB,
the only signal that exists i,son a radio frequency'but is ct
"carrier. anging aiJ
audio rate, above and below the suppressed
.lhe
voice in_
telligence is contained only in the upper (USB) or
lo*e, (iSÀ)
"sidebands".
For voicecommunications,ihesesidebandsare rimitedJo
about 3 KHz aboveand below the main carrier frequency.(The
limiting
o.ccursby filtering in the mike amplifiers and t-he .f,".p
fl ".v.t"j
filter.) For example on U.S. Channàl 1,26.965MHz,
the USB ;i;;;i
wou-ld.extend
up as high as 26.96bMHz + .003MHz - 26.96gMHz."The
LSB signal would extend down as low as 26.96bMHz _.003
MHz _
26.962 MHz. (3 KHz =.003 MHz for those of you who didn,t
realize I
convertedto make the math easier.)The pLL clrcuits must
thereforebe
able to offset themselves. slightly, mixing with the
ott ". ."quiràà
signals during-ssB reception or transmissilon. In addition,
the carrier
oscillator which providesthe carrier for alÌ modes(AM,
FM, SSB) must
also be detuned or offset slightly for SSB, (*) o. (_) as
appiopriate. In
this,way the mixing process will produce the correct
fr"qu".r"v fon-channel operation. The SSB offsàts are done very easily
ty "*it"hing in a small bit ofcapacitance or inductance whenever you
change the
mode switch' (This same detuning idea is used otr aiu o.
rirl rigJ trràl
have a front panel DELTA TUNÈ,control.)
- ò -

A very sharp IF crystal filter is neededfor SSB which will only pass one
of the two sidebands.This fiÌter is usually a large rectangular metal can
on the main PC board. The newer Uniden chassis has its filter actually
built on a small PC board which sticks up vertically from the main P(l
board. These filters are uery expensive becausethey use up to 8 quartz
crystals to get their sharp seÌectivity. Since you would need two ofthese
very expensive fiÌters, one for USB and one for LSB, it's much cheaper
to offset the PLL and carrier oscillators through the appropriate
switching rather than use two filters for two slightly different I I"
frequencies. In other words, a constant IF is maintained during SSll
use.The cost ofa few resistors,capacitors,transistors,or even a second
crystal osciÌlator is only a fraction of the cost of that secondIF filter'

F of 7.8MHz.
PLL, Cobra
r doing this,
ned.The fact
lar today is
Jreatreceiver
r (Eg, Cobra
Tersnot only
he troubleof
F. They also
usedfor each
rquilcs about
t e x a m p l ea
y too rvide for
ssrsyou get
LteSSR and
r versionsof
background
PLL mixing

The offset process will be very obvious as you study the SSB block
diagrams in Section III, and is also the reason you will see slightly
different VCO frequenciesshown in the rig's service manual charts.
The offset detuning in SSB is still not quite good enough during
reception,which is why SSB rigs must also have a front paneì control
"Fine-Tune", "Voice Lock", etc.The more common
called a "Clarifier",
"KC shifter". This circuit is nothing more than an
CB term is "slider" or
additional tuning inductance or capacitance wired in parallel with the
main USB,/LSB offset mixers. Think of it as an extra-fine-tune
adjustment to the offset mixing process. The range of most sliders is
and only wor-ks
factory-limited to about + 1 KHz from channel center, "strap
over" the
in the iìeceive mode. A very common modification is to
slider so that it will also shift during the Transmit mode' It's not only
very easy to do this, but also to increase the sìide range up to about + lr
KHz. (Detailed methods for doing this are described in our book, THFI
"SCREWDRIVER EXPERT'S" GUIDE.) Later vou'll seeexactlv how
the offset SSB mixers and clarifiers are connected in the PLL circuit.

e SSBmode.
or recerve)a
rverfor SSB,
lnging at an
he voice inower (LSB)
rrelimited to
The limiting
p IF crystal
USB signal
l8 MHz. The
.003MHz ln't realizeI
thereforebe
rer required
t, the carrier
f, SSB)must
propriate.In
'equency for
y by switchu changethe
FM rigs that

"()Dtl"
BRITISH
CHAI{I{ELS
THE
Many peopìehave askedhow the unusual U.K. CB channelsaffectPl 'l'
operation. The channels are 27.60125MHz at Channel I up to 27.9912;t
MHz at Channel 40, with standard 10 KHz channel spacings. The
answer is that the PLL itself has practically nothing to do with iti
Surprised?A big fuss was made over the belief that when CB was
recently legalized in Britain, the rigs would need special PLL chips' As
it happens, most rigs do have special chips but not becauseof the
unusual frequencyassignment.It would have beenjust as easy to use
existing chips. The fact that U.K. Channel I is 27.60125MHz rather
than a nice round number like 2?.600MHz is easily accomplishedin the
offset mixing process like that just described for SSB. This process ts
external to the PLL chip itself. A PLL is only intended to svnthesize or
I
L

- 9 -

generate the channel spacings. The additional l.2S KHz above 27.600
MHz (or 3.5 KHz below 27.605MHz if you prefer)can be set by tuning
coils in the rig at the factory, or by you with an external slider controì.
f'he new U.K. chips are identical to most of the latest American chips,
literally pin-for-pin the same functions. The onÌv differenceis in the
chip's "N-Code" set and the l.2bKHz offset detuning of aìl transceiver
stages shown in F'igure 3. (N-Codeswill be explained in great detail
later.)

THE
PLLF()R
FMUSE
The use of FM over AM or SSB is legally required in many countries.
Ironically it's now becoming popular in the U.S. where itls officially
illegal! Most of the very popular Europeanrigs (Eg, Ham Internationai,
Major, Superstar) are simply the basic American chassis with extra
channels and FM already wired in. The most popular current American
manufacturers such as Cobra, Midland, president, and Coìt have
jumped at the chance to expand their markets by adding the
same
circuits to their American chassis and exporting them abroaì. The pI_L
circuits of all these rigs are basically identical and the differences will
be pointed out as we progress.First though, let's seehow the pLL is used
for FM operation.
During reception, the FM,zPLL circuit is identicaÌ to any other AM or
AM/SSB rig. The PLL is only neededto provide the chànnel spacing
and selection, and the IF injection frequencies.To receiveFM, a Àpeciai
FM detector circuit is switched in. This circuit is typically a single lc
q1{ a few external parts having nothing at all to do with tt e pf,i. pn4,
AM, and SSB are alÌ detectedafter the pLL has done its job on the RF
carrier bv IF mixing. (special PLL chips such as the NEb6 i are actually
used as FM detectors,but that's another subiect entirelv!)
FM transmission is where our PLL's flexibility is used.The pLL circuit
uses a very sensitivestage called a ,,Voìtage-Controlled
Oscillator,,or
"VCO".
The smallestchangein the DC control voltage to a VCO circuit
will make it change its frequency.For the moment, just think of FM
transmission as a means of adding this smaìl voltage fluctuation to the
VCO. The fluctuating voltage is taken from the mike amplifier circuit
and is uer-ysmaìl compared to the amount of voltage that wouÌd shift
the rig to a completely different channel.
In addition this FM voltage is changing a t an audio rafe, riterarÌy rising
and_falling up to 3,000times per second.(Assuming the audio islimitea
to the 3 KHz maximum typical of two-way radio systems.) The
_10_

Tun
lreq

above27.600
ret by tuning
lider control.
ericanchips,
nce is in the
I transceiver
great detail

Ú,I G I IR T.::ì. O P' I'S h:'I' 7' L]N I N G T,'OB NON-S T'A N DA II I)
II.K.lil(]5. SSB. efc.

ry countries.
bis officially
rternational,
s with extra
nt American
d Colt have
ng the same
,ad.The PLL
ferenceswilÌ
r PLL is used

RX&TX
M IX ERS

rI

other AM or
rneÌspacing
rM, a speciaÌ
r a singleIC
hePLL. FM,
rb on the RF
are actually

ToRX&TX
Amplifiers

<-1

I



funed Coil

t

T u n e dC a p a c i t o r

: PLL circuit
tscillator" or
VCO circuit
think of FM
uationto the
rìifier circuit
; would shift

I

-=

T u n i n g c i r c u i t s o f l s e t V C O f r e q u e n c i e sb y p r o p e r a m o u n l l o p r o d u c e d e s i r e d
f r e q u e n c i e se. x t e r n a l o l h e P L L c h i p i t s e l f .

erallyrising
lio is limited
stems.)The
I

- - -t l -

word" modulation" simply means changing somethingin proportionto
somcthing else. Instead of changing the RF càrriàr
iouter in
proportion to the mike audio as in AM,zSSB,the carrier
friquency is
being changed in proportion to the mike audio. with FM tiansmission
we are simply taking advantage of the fact that the pLL's VCO is so
sensitive.

A B A S ICCR Y S TSAYLN T H E S I Z E R
'l'o

better understand what a pLL does,let's first compareit to the order
crystal-synthesizedmethod of signal generation.This is easy to do if
you think of the entire crystal or pLL synthesizer
as a ,,black box,,
within a larger biack box, namely the whole radio. Figure 4 illustrates
a
very common AM crystal synthesizer in biock diagram form. It uses
12
crystals to synthesize 28 channels. View the synthesizer within
the
dotted.linesas a single box rather than the three smaller blocks which
compriseit. In the next step we'll just replacethe internal workings
of
the big box with a PLL instead

N
Èl

F\
'q

In this arrangement there are two banks ofcrystals operating in the
l4
MHz and Z'l Mlz range. Changing the channel simply "oi.,bi.,".
u
different pair of crystals togethei. when each crystar u""t '" oscilrator
is combined in a mixer and passedthrough tuned circuits,
the sum
frequencv-of approximately 88 MHz is cholen. This 3g rvrrr"
sig"ai i"
sent to both a Transmit Mixer stage, and the First Recei.,". Mi*er"stage.
In the_Receiver
Mixer, the incoming 27 MHz signal is combined with ihe
lÌ8 MHz signal from the synthesizer. The difference frequency in the
1l
MFIz range (88 MHz - 27 MHz = 11 MHz) is chosenthi; tim; by tuned
circuits and bec'mesthe first receiverIF. This 11MHz IF is then passed
along to a second mixer where it's combined with the outo"l f;-;
separate f 1.730 MHz crystal oscillator. The difference frÀquency
is
chosenagain; this differenceis the standard 4bbKHzsecondìF *úich
is then detectedand amplified in the audio chain.
The transmit mixing is much simpler. The Bg MHz signal
sent to the
Transmit Mixer from the synthesizeris mixed with a separate
ll.27E
MHz Transmit Oscillator. The difference frequency if ZZ
MH, i,
chosen, passed through tuned circuits, amplified and moduìated.
Here'sa specificexample:For U.S. ChanneÌ 1,26.965MHz, the
Channel
Selector switch will connect crystals of ZZ.2}OMHz and 14.9b0
MHz.
t_w9
signals
mix
produce
to
a
signal
+
of 23.290MH z 14.}E}MHz _
]f 9se
38.240 MHz. In the Transmit Mixer, this 8g.240MHz signal will
mix
-12-



s

Fr
C,)

X

î)

f
\n
{

È

proportlon to
er power in
frequency is
;ransmission
,'s VCO is so



à K

a =
?

Y
ro
rat

3i

6 o
O E

N

ìe

I

E
o
(t

\

it to the oÌder
easyto do if
"black box"
I illustrates a
'm. lt usesl2
'r within the
rlockswhich
workings of

N

I
=

?

3

=
ra)
fq

t\
Òl

N

n
q

I

Fr

(D
It

N

E

3
q
t.ì

:ingin the 14
combines a
r's oscillator
its, the sum
Hz signaÌ is
Mixer stage.
nedwith the
ncyin the I 1
me by tuned
then passed
rtput from a
frequencyis
nd IF which

Llsent to the
ante 77.275
27 MHz is
.ulated.

H

p
O
U

a
{

I

l'
I
I
T
T
T
T
I
I
I
I
I
I
I
I
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t r l

I ' I I

1

I
I
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+ 6 8
I
I
-'e
6
I
I
J

+cé
ì.íoE
o

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I I I I I ' I I ' I

theChannel
14.950
MHz.
4.950MH2=
nal will mix

-13-

Ég
sa
= €
R rr.E

witlr the 71.275 MHz Transmit Oscilìator, producing a difference of'
26.965MHz which is the correct on-channel frequency.(38.240MHz
-11, .275 MHz - 26.965MHz.) Notice that the transmitted sign al is only
converted once in frequency, and this will also be true for PLL circuits.
However the receiver, being AM, uses dual-conversion for best
performance.So its signal is converteddown oncemore.The incoming
signal nf 26.965 MHz first mixes with the 38.240 MHz synthesizer
signal, the difference is chosen, and the result is the first lF of ll.27l:
MHz. (i18.240
MHz - 26.965MHz - 11.275MHz.) When this first IF is
then rnixedwith the separate11.730MHz ReceiverOscillator,the result
is 4r-rl-r
KI{2. (11.730MHz - 11.275MHz = 45b KHz.)
Earlier I mentioned that PLLs use IF frequenciesthat are usually
10.Éi95
MHz and 455 KHz partÌy becausea lot of existing tuning coils
were available.In this exampìethe first IF is obviousÌy11.275MHz but
in fact the tuning coils are stiÌl the same as they would have been for
10.695MHz; these coils can cover a wide frequencyrange. Iìemember
this when examining specific PLL circuits becauseyou may find that
the math for the IF's doesn't compute exactly; if the IF appears to be
slightÌy different from that calculatedor shown on the circuit diagram.
it's becausethese tuning coils are often detuned slightÌy to pass the
c0rrect frequency.

EQUIVALENT
PLLSYI{THESIZER
Now let's substitutea new "box" for that ofthe crystal synthesizer.1'he
internal workings of the box itself wilì be saved for Ìater. For the
moment, just picture it as a total unit and you'll understand it more
easily. F'igure5 shows a circuit which is almost identicaÌ to the crvstal
synthesizerof Figure 4. Alt the mixers and conversionsare the same.
'l'he
PLL synthesizer simply produces an exact signal in the 37 MHz
range, dependingupon the setting ofthe Channel Selectorswitch. f.his
signal goesoff in two directionsagain, to theTransmit Mixer and First
ReceiverMixer.
L)uring Transmit, this 37 MHz PLL output is mixed with a sign:rl
coming from a separate 10.695MHz crystal oscillator circuit. 'l'he
mixture passes through tuned circuits which select the difTerence
frequencyin the 27 MHz range and is the actual on-channelfrequencv,
similar to the previousexample.
l)uring Receive,the 37 MHz signal from the pLL mixes with the
-t4-

L difference of

, (38.240MIÌz
signaìis only
'PLL circuits.
sion for best
The incoming
z synthesizer
;t IF of 11.271-r
this first IF is
ltor, the result

N

I
Y
(o
ro

ra ;Èg:
E 6E
< o à

N

I
=

N

I

E

tt are usually
g tuning coils
t . 2 7 5M H z b u t
have beenfor
4e.Remember
may find that
appearsto be
'cuitdiagram.
ly to pass the

N
U)

r.ft

z
q

rI

t-

z
I

I
=

f,ì

t(l

r{

S
T-

?

I




=

E

F

l\

I

I I '

F

I
I
I
I
T
I
I
I
I
I
I
T

t

xes with the

ct

F-,

\\
\

vith a signal
: circuit. 'l'he
he difference
relfrequencv,

o
(D

.!
o

or
I



rthesizer.'Ihe
ater. F or the
stand it more
to the crystal
are the same.
r the 37 MHz
r switch. 1'his
ixer and F'irst

E

I

=

ì

x

o

,.cl
J Y

o-o
fD
-

I I I - I - I I I I

1

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Nl!

E

incoming 27 M}Jz signal to produce the first or high IF, which in this
case is 10.695 MHz. This signal then passes to the Second Receiver
Mixer. In this stage, a very clever extra use is made of the PLL box. It so
happens that almost all PLLs require a "reference oscillator" circuit of
I0.24OMHz to operate. By borrowing a bit of that 10.240M}Jz energy
and sending it up to the Second Receiver Mixer, guess what happens?
Here's the math: 10.695 MHz - t0.240 MHz = 455 KHzr. Once again,
we've managed to make a dual-conversion receiver. and with standard
tuning circuits.
Notice a small but subtle difference in my labeling on the right-hand
side of Figures 4 and 5. In the crystal synthesizer, the second receiver
mixer output says "455 KHz to AM Detector" while in the pLL
synthesizer it says, "455 KH zto AM or FM Detector.Why not FM for the
crystal version? Disregard the fact that FM CB is not tegal in the U.S.
and that CB had not yet been discoveredin the rest ofthe world where it
often is legal. The reason is purely technical. It's very difficult to
frequency-modulate a crystal oscillator for 27 MHz use; the crystals
can't be "pulled" far enough away from their cut frequenciesfor proper
FM deviation to occur. Commercial two-way FM radios that operate in
the VHF or UHF bands can be easily crystal-controlled because the
crystal is multiplied up many times in frequency for final operation.
When such a signal is multiplied up, any change in the controlling
crystal frequency will also be multiplied by the same amount. With th;
PLL, we use a VCO circuit that's very sensitive, and can easily generate
FM where a crystal-synthesized rig could not.

ELEMEl{TS
f)FTHE
PLLSYSTEM
Time now to look inside the mysterious "black box"; I can,t avoid it any
longer! If you're with me so far you'll have little trouble. The description
will be very basic here, getting more specific as we progress.
Trying to describe PLL operation is a little like the situation of giving
somebody a very small gift wrapped up in a very large box. There's a
box within a box within a box, all coveredwith wrapping paper. So far
we've only looked at the wrapping; time to seewhat's inside! Part of the
problem lies in the name, Phase -Locked,-Loop.There's no real beginning to a loop or circle, so it's possibleto jump in anywhere. Once you
understand what each main PLL element does, you can pick the
starting point that you prefer.
Figure 6 shows the basic elements of any PLL system. Arrows show the
direction of signal flow. It's obvious that the signal goes around in one
_16_

, which in this
cond Receiver
PLL box. It so
ator" circuit of
0 MHz energy
rhat happens?
r! Once again,
with standard
t

,heright-hand
econdreceiver
e in the PLL
not FM for the
gal in the U.S.
world where it
ry difficult to
e; the crystals
ciesfor proper
;hat operatein
'd becausethe
nal operation.
he controlling
ount. With the
asily generate

Ft

p
q



x

e
.n

,'a

J

Ft

Io

z

z

f
o-

z
{

U
q
{
=:

e.l
r't avoid it any
he description
ress.
tion of giving
rox. There's a
I paper. So far
de!Partofthe
s no real berere,Onceyou
can pick the

b

.È9

&

E(,

J:l

ttt ;i

È È

o

N

î
=
(\
ci

E
T

P
9
;iG

II p8

towsshow the
aroundin one

-17 -

big.circle-or loop. The order I,ve chosen to describe
each element is one
which I think is the easiest to understand.
ifrà-_u:o, building blocks
are:

'l'h
(()
I t's

tìot

l.
2.
3.
4.
b.

ReferenceOscilìator & Divider:
programmableDivider:
phase Detector;
Loop or Low_passFilter:
Voltage_ControlledOscillator(VCO)

()SCILLAT(]F
REFERENCE
& DIVIOER
This circuit connects to the,outside_world
through an ordinary crystal
oscilìator.

The very newestchips have i"t"r"li "."il"i"i.
irr"ì"""ii
that's.needed
is the crystalitseif a;; , i"* "ó""itors. However
the

majority of chips in current use still need
a' u"tuur t...rristor oscillator
circuit

with th"^"Iyit-"1:Jhl..os"ilfator op"rrìJ.if_.rt,rniversally
at a
trequencyof I0.240MH_r, felyerv oìd dusigns
used
other
!S_
órhl;
such as E.l2 MHz or 10 MHz.)
,,digiral,,
Tho ;"u;;;l;il"",r."
with
eÌectroniccircuits,it's verv easvto divider.ignàl
orro.zaónrui frvti"
number"1,024".If this is don", itru.urulii. u.,?ulput
r.om the divider of
10 KHz, (1,0.240
MHz -.- \0?4 = 10 KHzf;hich lrr"t t .pp".r" to
be the
required channeÌ spacing for most of ti" ;;;ii'.
cg
"é."i""r.
so-"_
times a few channersskip around bv 2o o.3o
KiL but this is accounted
for in the next section,tÉe p.ogrrmm;;I"
ó;;;..
j^Xa-iddisital techniqueswere used with pLLs. .I.his word ,.digital,,
relers to any electronic circuit tlat can
only recognizeone of two
,,/and
states,
,,O,,,,,HIGH,,
which
are
typicalty
calted
91"1i_f:! "oN',
"Low",
and
or
and ,,or.F". Tú"[;i;
aìgiiàr a",,i"" as simply a
switch, such as the ON/OFF,*it"f, or, À!,ì;:
il" electronicopposite
of digital is. "analog',, which is , "ir";;l
t'h;; ".., "rru.rg" its values
continuously from each-possible"*i."-"
,"a theoretically has
of possible values. Th" tóiúùd^"o.,tror
is an analog
h::ff;"d"
Many-of the most recent chips actually use
the
srgnaì^todividedown bv 2,0ía,givingà aì"ij", I0.240MHzreference
than l0 KHz. And somechips"ur, ,"tit "iihà" ""tp"t of b KHz rather
a-r"i"io" ,"tio. The 5 KHz
steps make certain PLL function" u""i".
ìo à"co-pfi"fr, as we,ll see
later.

s()
I'I,

('fy
loo

PR

'l'lr

îre(

(:oIl

('on
thc
te<r
nur

rìLlf

[)ro
a lrr

I.la

<li,r

("(-)

c'irc
prol
I)ia
prol
gra.
cha
( lod
ordi
sup
and
new
irnp

PHA

'l'hi

fron

-18_

elementis one
ruilding blocks

'fhe purpose
of the Reference Divider is to provide a very stab.lt,
r'omparisonsignal against which all other signals will be synthesized.
It's obvious that if the 10.240MHz signal is not exactly on frequency,
none of the other PLL signals will be either. So all PLL circuits have
some way to trim their outputs to the correct frequency. The majority oi'
PLLs use a small value trimming capacitor or coil in the reference
crystal circuit, although a few PLLs make the adjustments later in the
loop.

PRf)GRAMMABLE
DIVIOER
'f
rdinary crystal
rtors where all
l. However the
;istoroscillator
rniversaÌÌyat a
. other crystals
with "digital"
140MHz by the
n the divider of
rpens to be the
rervices.Someis is accounted

word "digital"
ize one of two
"HIGH" and
,
ce as simply a
tronic opposite
Lngeits values
rretically has
, is an analog

MHz reference
rf5 KHz rather
rtio.The5 KHz
h, as we'll see

his is reaÌly the heart of the PLL synthesizer,and a common sourceof
frequency modifications and expansions in most older chips. Iìy
connection to the outside world at the Channel Selector switch, a
command is made to divide down whatever signal it's receiving from
the VCO by a precise number. This number is generated using digital
techniques and is called an "N-Code", "-: N", or "Divide-By-N"
number. The N-Code is a number based upon the digital or "binary"
number system rather than the common decimal system used b5'
people. The word "binary" refers to a pair of two things and it was
already pointed out that a digital circuit can only recognize two states.
Each position of the Channel Selector switch changes the N-Code
slightly by connecting either a positive DC voltage ("1") or ground
("O") to the appropriate IC pins on the PLL's Programmable Divider
circuit. There are typically 6 to 10 pins on the chip devoted to the
programming function. On the cover of this book is a chip's Block
Diagram showing "P," to "Pu"; the "P" stands for "Program". The
programming pins are called "bits" and the total number of programming pins or bits has a direct relation to the number of possible
channels which can be synthesized. Many times a special type of NCodecalled "Binary-Coded-Decimal"or "BCD" is used instead of the
ordinary binary code. This is partly becausethere's a lot of electronic:
support hardwàre around using BCD inputs, such as keyboard controls
and [,ED number displays. It's also becausewhen used with the verv
newest chips, BCD programming helps make modifications almost
impossible.

PHASE
OETECTflR
This circuit is the decision-maker in the PLL. It receives two signals
from both the Reference Divider and Programmable Divider and
-19-

compares them, Ìooking for an exact match in the divided-down
frequencies. The ReferenceDivider will usualÌy be exactly 10 KHz or
5 KHz. (10.240MHz -. I,024 ot 2,048.)However the input from the
Programmable Divider may not necessar y be these exacf frequencies,
in which casean error exists.The phase I)etectoris intended to sense
this error and do something about it. when inputs to the phase Detector
are not matched,the loop is said to be,,unlocked',or,,searching.,,The
Phase Detectormust bring the loop into lock by an appropriateoutput
command to the VCO. This command is in the form ola vàry small bC
correctionvoÌtage,1+1or (-) as required.Most phase deteciorshave a
secondoutput calìed a "Lock Detector".If a great error exists between
the compared signals that can't be correcteàin the normal way, the
Lock Detector switches to its opposite Ìogic state. For exampÌe,ii the
Lock Detectoris normally at a logic ,,t', oi hign DC voÌtage,Àe out_of_
lock condition will causeit to switch over to the "o" or gróunded state.
This change is sensedby an externar switching circuii that's usua y
wired to turn off the transmitter (and sometiÀes even the receiveri.
preventing off-frequency or unstable operation. How far the loop
cal
vary within its normal lock-up frequenciesis called its ,,capturera^nge.,,

b5
is

L()f)P
{)RLOW-PASS
FILTER

th

This circuit immediately follows the phase Detector,and is designedto
smooth out the digital waveform entering the VCo circuit. Becausethe
Phase, Detector is sampling and compaiing inputs at a digitaÌ rate,
literally millions of times per second, thàre will always be high_
intensity "spikes" c.ming out of it. It's impossibre for any erectricaior
mechanical device to switch on and off initantaneouslyj you can,t go
from zero to some higher value just like that. (No doubt yóu',re seenyolr
house lamps dim slightly when a Ìarge motor like an air-conditioning
compressorsuddenly switched on; it took time for things to equalize.)IÌ
these spikes were allowed to pass on to the VCO, they could-causeíhe
oscillator's frequency to "jitter" around unstabÌy. The spikes are of a
hìgher frequency than the normal digital pulsel and thàt,s why this
element is often called a Low pass F tér. It sìops high frequencieJfrom
passing through it. This is exactly the same idea asthe Low pass filter
used on the back of a rig which prevents high frequency harmonics
from causing TVI.
The.T.oop.Filter may be a circuit as simple as a capacitor/resistor
combination at the output ofthe Phase f)etèctor, or it can take the form
ofan actuaÌ "active filter" inside the chip itseÌf. The active filter is now
more common as engineers figured out how to cram more and more
functions int. the chip structure itself. This simplifies design (and cost!)
-20-



vt

'tl

bt
St
n(

St

S€

v(
th
ul
b(
I)

B

g(

t)
di

SC

th
{-

in
fr
sI
I)

F(
IS

re
th
th

(i{
Ì..

TI

vided-down
y 10 KHz or
ut from the
[requencies,
dedto sense
aseDetector
ching." The
riate output
ry small DC
:tors have a
sts between
ral way, the
Lmple,if the
e,the out-ofundedstate.
at's usually
re recelver),
,heloop can
turerange."

designedto
Becausethe
ligital rate,
rs be highelectricalor
zoucan't go
i7eseenyour
onditioning
equalize.)If
ld causethe
kes are of a
is why this
Lencies
from
v Passfilter
harmonics

torlresistor
rkethe form
filter is now
'e and more
n (andcost!)

by reducing the number ofexternal circuit parts needed.The Loop Filter
is sometimes called a "Charge Pump" because its input capacitor
charges up to help keep the output waveform very pure.

v0LTAGE.C0t{TR0LLE0
0SCtLLAT0n
fVC0l
The VCO is a very interesting circuit that has many usesin electronics
besidesCB radios, such as the Automatic Fine Tuning (AFT) in a TV or
stereoreceiver.The VCO is an oscillator whose frequency is determined
not by the usual coils, capacitors, or quartz crystals, but rather by a
special device called a "varactor" or "varicap" diode. It's extremely
sensitive to the slightest change in DC voltage applied across it. As the
voltage increases,the diode's internal capacitance decreases,changing
the VCO's frequency. Increasing the voltage can make the frequency go
up or down depending upon how the varactor is wired in the circuit, and
both methods have been used in CB VCOs. The output of the Phase
Detector looks exactìy like a "staircase" of DC voltage levels when
going through the range ofchannels, and the tiniest step up or down
wili shift the VCO to the next channel. If you measured this voltage at
the chip with a voìtmeter, you'd find a change as small as .05 volts DC
will shift an entire 10 KHz over to the next channel!
Becausethe VCO is so sensitive to voltage changes, we can make very
good use of this fact for FM transmission, SSB slider circuits, and
Deìta-Tune controls on AM,zFM rigs. If you study the schematic
diagram of such a rig, you'll always find an extra varactor diode
somewherein addition to the one used in the VCO itseÌf. Figure Z shows
this general idea. For the SSB slider or Delta Tune, a control on the rig's
front panel is used to change a DC voÌtage across a varactor diode; this
in turn changes the varactor's capacitance slightty and therefore the
frequency too. (A much more detaiÌed explanation of slider circuits and
specific popular chassis modifications can be found in THE "SCREWDRIVER EXPI]RT'S" GUIDE.)
For FM transmission,someof the audio from the mike amplifier circuit
is sampled off to be used as a control voltage. This voltage, which
rememberis changing at an audio rate,ís appliedto another varactor in
the VCO or Mixer stage at a sensitive place. The result is FM rather
than AM or SSB.

Continuing around the loop, you'll seethat the VCO's output is fed right
back into the Programmable Divider and then to the phase Detector.
The Phase Detector then decideswhether or not a 10KHz (b KHz) match
-21 -

FIGIIRt,:7. {rsING 7'HL: SI,)NStT,It/b)
l/(:o sl,AGE
T0 pgoDtr('t:

ssB/Dú)LTA_TUNE
Ot,p_ilrs oR r,.M

To RX & TX Mixers

V C O / Mt X ER
srAGE(S)

C l a r i f i e ro r
Delta-lune Control

t

* DC Control
Voltage
at Front panel

4
I

,,VARACÎOB''
DIOOES

MIKE

:

RX

o

AUDIO
AMPLIFIER
STAGES

To speaker (RX mode) or modulaled
RF stages (TX mode)

-2r-

fAGh)
oR t-M

& TX Mixers

O/MIXER
'AGE(s)

exists between the ReferenceDivider and the Programmable Divider. If
so, the loop is ìocked on frequency. Ifnot, the Phase Detector sensesthis
difference and outputs a DC correction voltage to the VCO. This drives
the VCO up or down slightly in frequency untiì an exact match is found
and the loop locks. This entire PLL process can be compared to a
self-correcting mechanical servo system for those of you who are
mechanicalìy inclined. Although it may take many comparison cycìes
before an exact match is found, the entire processhappens in the wink
of an eye!

You really begin to appreciatethe accuracy ofany PLL system when
you can compare it to the older crystal-synthesized rigs. For examplt:,
using an 8-digit Frequency Counter, I compared the carrier frequencv
accuracy of both types. Where the crystal rig might indicate say,
26.965316MHz on Channel 1 and 26.975124MH2on Channel 2, the
Pt,L rig will typically show something like 26.965004MHz on Channel
1,26.975004
MHz on Channel 2, and.27.405004
MHz on Channel 40. In
other words, the PLL is accurate all the way down to the last decimal
place!

We've now come full circle around the loop and hopefully you're still
there. It's now necessary to complicate things a bit more because
certain other PLL circuit functions must be explained to complete your
basic understanding.

THE
Lflf)P
MIXER
f)RO(]WII
Cf]I{VERIEF
The needfor Intermediate Frequenciesand SSB offset mixing has been
expìained. You've also seen how the very sensitive VCO circuit can
change the carrier frequency, slide an SSB clarifier, and generate FM
transmission. However there's still one more basic mixing process
requiredin the majority of rigs that use the older chip technology. While
this processcomplicates the circuitry, it also makes modifications a lor"
easier!

) or modulaled
mode)

The extra mixing circuit is caÌled the "Loop Mixer", "Down Mixer", or
"Down
Converter". Figure 8 shows its addition to the basic PLL circuit.
Notice that exceptfor the addition of this extra mixer, the PLL circuit is
identical to that of Figure 6 on Page 17. A separate crystal-controlÌed
oscillator provides the extra mixing signal, and may be used directly or
multiplied up to get it close to the VCO frequency

_23-

'fh

tht
thr
37
dip
ne
ar(

rÈl
'* =

I

ò
x

E : E
3 " o
o
o

LJ T

evl

I

bo
th(
cr]

Fi

q
o
-=

X

e

Fo

o

s(,

o

o
J

F.i

z
-o
R

F

F.'.

p

4

q

x
=

\-ì
{

È

z

lor
s\!
far

s;Ii
SS

col

ofl
Re

'r'h

r\
ta

I

a

o '

. o
J:l

\

E à
E(/,
a r g

os(
on
dif
c:l-i

Th
Mi:
act
cor
mu
the
t()
pli(

TH
In

-24-

The reason many older Pl,Ls require this extra mixing processis that
they were not able to directìy divide down the incoming VCO signal trr
the Programmable Divider. Most common VCOs run in the 16 MHz or
37 MHz range, and a frequency this high was impossible for older
digital dividers to handle; they just weren't fast enough.Nowadays the
newest"CMOS" PLL chips have beenimprovedto the point where thel'
are able to divide down a signaì as fast as 20 MHz. Such chips are
typically found only in AM or FM dual conversion rigs. You'lÌ
eventually learn to hate this particular technologicaì improvement,
becausethe Down Mixer stage was one of those perfect spots to modifv
the rig's frequencies by injecting a different mixer signal with another
crystal.

o

z
g
tt
F

=
x
E

z
3

For SSB use,the f)own Mixer is again offset sÌightìy in frequency,as
seenin Figure 9. When you switch to LSB or USB, separate coils and/or
capacitorsare placed in the circuit whose values will detune the main
loop oscillator by the correct amount. 'l-he offset circuits are typicaiÌy
switched in by diodes or transistors, and may have fixed values or
factory-adjusted trimmers. In most rigs the varactor circuit which
slides the Clarifier is also connectedhere. However there is one current
SSB chassis (with uPD2824 chip) where the 10.240 MHz crystal
connectsto the Clarifier but a separate oscillator crystal is the one
offset for the carrier itself. (Flg, Cobra 146GTL, President AR-141,
RealisticTRC451, Sears6611.i1810.)
The Loop Mixer usualìy takes a signal generated from some other
oscillator and mixes it with the VCO signal. Tuned circuits then pass
only the difference frequency on into the Programmable Divider. This
differencefrequency is low enough to be handled by the older type of'
chip dividers, and is generally in the 910 KHz to 4 MHz range.
The crystal-controlledosciìlator signal that's injected into the Dowrr
Mixer can come from severalpossibÌesources.The most obvious is an
actual crystal oscillator using a transistor, and this is still the most
common method. In many cases, this crystal frequency must be
multiplied up by tuned circuits to get it close to the operating range of
the VCO. The most common multiplication is by a tuned coil designed
to double or triple the crystal frequency, although higher multi'
plicationshave been observedin somerigs.

TH5
E. 1 M
z00P
2 HL
M I X I N0G
UTPUT
In many newer chips, there's a provision right on the chip itself for a
signal that can be used for loop dorvn-mixing. This signal is typicalÌ5,
-2b-

ha
5.
an
tri
clr

FIGURE 9. OT-FSETTING PLL FOR SSB MIXING

US

To RX & TX Mixers

í.1

an
lts
to

be
V C O / MI X E R
STAGES

CU

Lct
Ior
rvh
bet
I )i.
pr(
oul
thr
ex(
the
vet
<rh
stil
req
corl

Indivldualcoils,capacilorc,
or even crystals may be
switched in heÌe.

SP

Thr
dea

O O W N M I X E RI N P U TS I G N A L S

0pe

bec
pin

N O T E : l h e C a r r i e rO s c i l l a t o rs l a g e i s n o r m a l l y
o f f s e ta l s o i n a s i m i l i a rw a y .
T h i s m a i n t a i n sa s i n g l e l F t r e q u e n c yr o r a l l m o d e s
and thus only a
s i n g l el F l i l t e r i s r e q u i r e o .

THE

Thi

-26_
lr.-

XING

half the 10.240MHz ReferenceOscillator frequency, or 5.12 MHz. The
5.l2MHz signal comesoff a pin right on the IC chip; it's already been
amplified and buffered internally. The 5.12 MHz signal is normallv
tripled to 15.360MHz (5.12MHz x 3) by a tuned coil,which pÌacesit verv
closeto a VCO running in the 16-17M}Jzrange.In a few Motorola rigs
using the TC9105chip, the VCO is running in the 37 MHz range, so the
5.12M Hz is multiplied up by 7 times to get it near this frequency. And in
another very common arrangement, the 10.240MHz master oscillator
itself can be doubled.Borrowing this 10.240MHz energyis a simplewav
to provide not only receiver IF injection as we saw earlier, but can als<r
be used to run the loop mixer itself.

C U R R ETIE
{ TC H N IT
CR
AE
LN O S
Loop mixing is one easy place for frequency modifications. Unfortunately the newest chips (Eg, LC7737, LC7136,TCg109, TC9119)
which are usedfor dual-conversionAM or FM rigs have no loop mixing
becausethey are capable of direct VCO division in their Programmabltr
Dividers. In addition they use special programming tricks to furthcr
prevent modifications. If you own a rig with one of these chips, you're
out of luck at the moment. There are however still millions of rigs out
there using Ìoop mixers. Many are obsoletenow but the most notable
exceptionsare the PLLO2A, MB8719, and uPD858 chassis,which arc
the most popular rigs in worldwide use,for obvious reasons!The ANI
versions of these rigs have generally disappeared because the newer
chips are more fooìproof. But the SSB versions are very common antl
still being marketed almost everywhere. That's because SSB usualll'
requiresloop mixing at this point in PLL technoÌogy, and details ol
common modifications can be found later in this book.

FUtICTIl)t{S
SPECIAL
CHIP
There are severaÌ more options which may be found on PLL chips' Most
deal with resistance to illegal modifications, easeof circuit design, ancl
operatorconveniencefeatures.I'll briefly summarize some of these here
becauseyou'ìl need to understand them whenever you're studying thtr
pin diagram of a particular chip.
a similiaw
r ay.
n d t h u so n l y a

THT
ER A N S M I T / B Ef TCl E
IIVHEI F T
RS
This is a function found only in the very latest generation of chips
-27 -

designed mostly for AM or FM with dual-conversion receivers.
Examples are the LC7l20,LC7t30/31, LC7186/57,TC9106, TC9109,
TC9119,uPD2814,and uPD2816.A specialIC pin shifts the N-Codeto
the Programmable Divider when that pin goes to its opposite logic
state.

I'veo
rvith
'l'ran
îronl

l6M
doub
LI.K
rnste
lri N'I
s:ìm€
d esip
pe a k
tune
was
rnocl
beto

For exampìe,the chip may have one set of N-Codeswhen the T,zRpin is
grounded("O") and a different set of N-Codeswhen the T/R pin ishigh
with +DC voltage applied(" 1"). You'lt find the chips with this featurein
any rig having only a single 10.240MHz ReferenceOscillator crvstal.

Becausethere is no other signaì present in the loop that can be used for
mixing, receiverIF injection, etc., it's necessaryfor the chip itself to
generatethe 455 KHz shift used for the receiver'ssecondIF stage.The
T,/R pin is connected through transistor switching circuits to the mike
and sensesthe T/R change.When this change happens,the output of
the Programmable Divider entering the Phase Detectoris of courseno
longer matching the ReferenceDivider's output. The phase Detector
then outputs its correctionvoltage to the VCO , driving it up or down to
lock the loop. Generaliy the VCO is driven 4b5 KHz higher in the
Transmit mode.

MISP

Man
i ll eg
pr()g
tunc
be us
once
bene

Chips with the T,uRshift are rarely used with multimode rigs having
SSB, because SSB doesn't require the second 4b5 KHz receiver IF
conversion.One exception at the moment is the U.S. versions of the
Midland 6001/7001.They use the uPD2816chip, which has a T/R pin,
but the pin is not connected; instead a separate crvstal downmixer
oscillator is used, which makes modificàtion easy again. So it's
possibìe,depending upon àou the chip is used, to modify rigs that are
generally non-modifiable. (Later versions of the 600I/7001 use the
uPD2824,which is pin-for-pinidentical to the uPD2816minus the T,zR
pin function.)

FREO

'l'hi s

KHz
" 1 "r
;Kh

r(]atl
freclr
Rerm
othe
and
mod.
ICs l

The T,zR families of chips are among those first mentioned using an
internal 5 KHz ReferenceDivider output signal rather than f0 KHz.
The standard 10.240MHz crystal is used,but this time it's divided down
by 2,048.(10.240MHz = 2,048 - 5KHz.) This is necessary becauseit's
easy to get the 455KHz shift; by increasing the N-Code g1 counts from
the ReceiveN-Codes,the resuìt is 91 x bKHz - 41bKHz. Somechips shift
5 KHz/2.5 KHz for T,/R purposes.(Eg, PLL08A, PLL03A, TC9109.)

-28L.

ton Iecelvers.

9106,TC9109,
theN-Codeto
oppositelogic

the T,rR pin is
',uR pin is high
this featurein
illator crystal.

:an be usedfor
: chip itself to
I IF stage.The
its to the mike
r,the output of
is of courseno
hase Detector
; up or down to
higher in the

le rigs having
lz receiver IF
ersions of the
las a T./R pin,
al downmixer
rgain. So it's
y rigs that are
/7001 use the
ninus the T,/R

rnedusing an
than 10 KHz.
divideddown
'y becauseit's
1 countsfrom
mechips shift
r, TC9109.)

I've observedtwo other variations of the T/R shift idea. In the U.S. rigs
with the TC9109 chip, the N-code shifts up by 2,139 counts in the
Transmit mode while at the same time the Reference Divider shifts
from 5 KHz steps to 2.5KHz steps. This drives the VCO down from the
16 MHz range usedin the Receivemode to the 13MHz range, where it's
doubled to produce the direct on-channel frequency. In the LC7136/37
U.K. rigs, the Reference Divider never changes its 5 KHz steps, but
instead simply shifts down by enough counts to drive the VCO from its
16Mhz Receiverange to the 13 MHz range where it's then doubled in the
same way to produce the direct on-channel 27 MHz frequency. Both
designs use an IC mixer where the various VCO outputs can either be
peaked (16 MHz Receivemode) or doubled (27 MHz Transmit mode) by
tuned coils. The PLLO3A (now obsolete)worked on this same idea but
\ì/as way ahead of its time; when people discovered the rig couldn't be
modified, sales of that chassis disappeared. The chip appeared long
before the FCC made manufacturers use such advanced ideas!

MISPRÍ)GRAM
Cf)llE
fMCIPII{
Many of the newer chips have special N-Code protection to prevent
illegal modifications. If you try to force an illegal program code on the
program pins with non-acceptablevoltages and grounds, this pin
function is activated. It's very similar to the Lock Detector in that it can
beusedto turn off the transmitter unless a legal program codeexists. So
onceagain, some ofthe extra "features" in the newer PLLS are for the
benefit of the manufacturer and the ìicensing government, not for you:

FREOUETICY
SELECT
IFSIPItI
This pin, available in someolder chips, allows selectionof 10 KHz or 5
KHz ReferenceDivider steps.The division is chosen by the appropriate
"1" or "O" on
this pin. Don't confusethis function with the needfor the
5 Khz division usedwith the T,zRshift; it's not for the same purpose.The
featurewhen usedin the new ROM chips allows designersto synthesize
frequenciesin 5 KHz offsets for SSB use in addition to AM/FM use.
Remember,the earlier chips were applied to CB synthesizers ond many
other kinds of equipment such as VHF marine radios, aircraft radios,
and signal generators. It was only when people went wild with CB
modifications that manufacturers were forced to make snecial "dedicated"
ICs for CB synthesizers only.

-29 -

Before you get all excited and think you can turn your rig into one
having 5 KHz channeìs by changing the voltag" or, thi, pin, consider
the fact that the N-Code programming must aÉo change to produce b
KHz steps in the Program mabÌe Divider circuit as well. it can-,tbe done
easily! This pin for cB circuits will either be left unconnected on the
printed circuit board, or connected to grouncl or +DC as necded to
produce 10 KHz channel spacings.(NOTE: FrequencyExpanrìerslike
the MICROMONITOR and MICROSCAN haveiheir òwn pLL circuits
which will replace the rig's PI L circuits, and that's why they can
producecontinuous5 KHz steps.)

AUTf]MATIC
CH.g/CH.
I 9 C()MMAIIIl
This is a special feature found oniy in the very Ìatest chips, like the
LC7I30/31 for American rigs, LC7t3b for 22-channeÌEEÒ rigs, and
LC7136/37 for British rigs. By applying a +DC voltage to thàsé two
specialpins, channel g or channel 1gis automaticalÌy recalledwithout
changing the ChanneÌ SeÌector.you can just push a button, or the pins
can be connectedto a scanning circuit to Àtopon thesechannelswhln a
signal is present. In addition they're "or,.r""t"d internaly to the MISPROGRAM CODE pin. If the MC pin is not used, as in some chassis
variations, attempts to force an illegal program code will cause either
Ch.9 or Ch.t9 to be recalled instead of Hlli"g the transmitter. When
these features are included in the rig model, tÉe MC pin will be tied to
the Lock Detector pin to kill the transmitter. If these features are not
included in your rig model but you,d Ìike to have them, it,s a simple
matter of fitting a SPDT switch betweenthesepins and a +DC voltage
source.(SeeFigure 12,Page 47.)

SCAI{I{I
t{GIIITERFACE
Certain chips such as the LC?120 and those just mentioned can be
connectedto special scanning chips to scan up and down the legal
band, search for an unused channel, etc. These àre useful features Ìor
some people and are often found in rigs having all controls in the mike
"guts"
remotely hidden elsewherein the car. (Eg,
1nd,!h9 main radio
RealisticTRC462 "One-Hander".)The advantagesand disadvantages
should be obvious bv now.

-30i-

' rig into one
pin, consider
: to produce5
can't be done
nectedon the
as needed to
rpanders Ìike
r PLL circuits
rhy they can

hips, like the
IEC rigs, and
r to these two
ralledwithout
rn, or the pins
rnneìswhen a
ty to the MISsomechassis
.l causeeither
mitter. When
will be tied to
ltures are not
, it's a simple
l +DC voltage

tioned can be
rwn the legal
ul features for
rlsin the mike
r the car. (Eg,
lisadvantages

SECTION II
BACKGROUND FOR
MODIFICATION METHODS

Now^we'reready to get to the.g_ood
part you'veprobably all beenwaiting
f o r i S e v e r a lw a y s t o . . t r i c k " - C B , i g " i " t o
t h o s eh i g h a n d l o w
"fu11V"
c ; i ì ; ; ""o.,u..srons,
-FIu-channels, as well as l0 Meter
will be
explained in this section.

A

cl

h

c
C
(l

There are stilÌ two basic.methods of
changing f requenciesin the
majority of CBs. At this writing, th" fooìp;;;ì;".ig.,.
Ìru'u.rot exactl.y
flooded the market. esnecially ió. SSe
;", ;Jìi".utor"
mosr rigs can
be modified using these tricks. These t.i"-k.
;;;;"'

T

n
tl
tl

1 . Clange the Programming N-Code on
the pLL chio,s
p ln s ;
Change the Loop Mixer signal.

S
a
P
p
S

It's not the purpose of this book
to teach the basics of. aligning
transmitters and receivers, so if
;lou,re p_lanning a large il;;;;
corversion such._asup into the 10 Meter
Ham band, reaiignment of
other circuits will also be required. A
schematic circuit diagram of the
rig is essential.However for adding """
".ìi"
iaditional 40-channel
segments to most ries. the orly alignment
usually requirJ i;l;-;ir;
PLL's tuning circuits themser"es.rh"is parl
i"-i"rlrp to
with the aid of the circuit schemuti" .;;;;;;1ìperienced vou to figure out
friend.

d

Before getting more specific, I think it,s
important to describe an actual
PLI-. circuit to make Àur" you understand
it.-""-pf
"' *" operation. Let,s
walk through the complete circuit, .tup
tt;1;.

F
n

T
tl

A TYPICAL
SYI{THESIZER
CIRCUIT

b
b

Refer to Figure 10 on page 84, which is
the pLL circuit ofperhaps the
most popular AM PLL rig ever made.
It's r""" "ora under dozensof

Ir

:l t^

brand names and uses..ihe """r_pof"iu.ilibza
pLL chip. The
AMISSB or AM.zFM,zSSB"a.iatiois?tiri,
ll'r"rs are very similar
when you consider the
"hr;;;;
"""a"Jr". SSB offsets and
-minor
slidersand FMing the VC_O
ci.""it. io-Jif uì.riJ.eferring to Chart 1 on
page35,which is a breakdownof all the
iÀportl.,t
by channelnumber.Sucha chart is;;;;i;;;uded op"ruti.rgconditions
service manual but certain facts not ."iàì"J-ai*"ily with the radio,s
to 4O-channel
operationare often left out. I,ll be fiiling i" tfr"
_i."i"é bla"ks f;;;;;.

1

cl

rl

b
P

P
'l:

I beenwaiting
high and Ìow
rions, wiÌl be

snciesin the
uenot exactly
mostrlgs can

, chip's

; of aÌigning
ge frequency
alignment of
Lagramof the
ll 4O-channeÌ
ired is in the
r to figure out
rd friend.

A PLL circuit may be categorized very generally by the number of
crystals it uses and by whether its VCO is running for low-side or
high-side receiver IF injection. This example is actually the second
generation PLLO2A AM circuit; the first one used a 3-crystal loop and
can be found in Section III. The newest chips use a singÌe 10.240MHz
crystal and low-sideVCO operation in the 16-17MHz range where the
VCO can be directly divided without a loop Down Mixer.
The key to synthesizing aÌÌ the requiredfrequenciesis in the Programm able Divider, which is the only PLL section that you can control from
the outsideworld at the Channel Selectorswitch. That switch is where
t h e w h o ì el l r r ) (e s sì r e g i n s .
Supposeyou choose tJ.S. ChanneÌ 1, 26.965MHz. (This description
appÌies to all circuits and chips.) In the Channel I position, the
Programmable Dividel receivesa very specific set of instructions at its
programmi ng pins, which are directly connected to the Channeì
Selector.This particular instruction set, called an "N-Code", appÌies
only to Channel 1 and is nothing more than a number which will divide
down any signal appearingat the ProgrammableDivider input by that
number.

BII{AR
PY
R(]GBAMMING
'ibean actuaì
:ration. Let's

I perhaps the
ler dozens of
L chip. The
very similar
i offsets and
to Chart 1 on
rg conditions
bhthe radio's
r 40-channel
anks for you.

Referring now to Chart 1, you see the N-Code for ChanneÌ 1 is the
number "330" and the numbers progressdown to "286" at Channel 40.
The number 330 is the direct result of applying a +DC voltage of
typicalÌy 4-8volts to certain PLL program pins whiìe grounding certain
other pins at the same time. Recall that the PLL requires a digital or
binary counting system rather than the common decimal system used
by people.
In a binary number system, each successiveprogramming pin or "bit"
is worth exactly twice (or half) that of the pin next to it, such as 1, 2, 4, 8,
16,etc.A series of " 1s" and "Os" appears in the chart for each of the 40
channels. The " 1" means +DC is applied to that pin, and the "0" means
that particular pin is grounded. The greater the "Power-of-2" controlled
by a pin, the greater its "significance". As you'll see next the greatest
Power-of-2for this example is 256 on Pin 7. Therefore Pin 7 is called the
"Most Significant Bit" (MSB) and the "Least Significant Bit" (LSB) is
Pin 15,which only has a weight of 1. A chart like Chart 1 that shows the
logic states ("1" or "0") ofeach PLL program pin for each channel is
-33-

E

E =

È

s<;

!rf
E

s /

U

=

: t
* t

=

È

- >
- € - ! J

È È

=

..\n

=

v x


t,.- 4

=

F

J

N--

9ta
l ?

i \ i
È r ì

z ì
aa{

o

. . f

\\-.

o
(\l

3
'r
, r N

=

J
J

È \ :
+ " 1

< :

=

?7

h t
F

= -

z =
ì o

\

d \
r,

-;q!

= i ;

è^-

N(

e
a
* * a

ò

.

9

=

El

e 6

T

I

L-

C H A R T1
r e s c r i b e di n T e x t
C i r c u i tC o n s t a n t &
s T r u t hC h a r lF o r S a m p l eP L L S y n t h e s i z eD

Chanfel Channel
J r e ql l v H z l
No
l

2
3
4
5
8
9
10
tl
12
13
l4

r5
t6

=
ió .'i
< =

Ò a
=

è

= =

l o

1l
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39

26965
2 69 / 5
26985
27005
27415
21 425
27035
27055
27065
27475
27085
2t 105
2t-1i5
27 125
27 135
27.155
21 165
27 175
2 71 8 5
27245
27.215
27225
21255
21 235
27245
27265
27215
21 285
27295
27305
27315
27 325
27.335
21345
27355
27365
21.315
27.385
27395

'N"

d i qt a l v c o l r e q
codes (MHz)
330
329
328
326
325
324
323
321
320
319
318
316
315
314
313
311
310
309
308
306
305
304
301
303
302
300
299
298
291
296
295
294
293
292
291
290
289
288
287

17.18
1 71 9
1 72 0
1l22
1 /2 3
1 72 4
t 72 5
1i2tt 72 9
1 73 0
1 73 4
1 73 7
1 73 8
1 73 9
1 74 0
1 14 2
1i43
1 74 4
1 14 7
r 74 5
r 74 6
17.48
1 74 9
1 75 0
1 75 2
1 75 4
1 75 5
1 75 6
r 75 8
17.59
1 76 0
1 76 1

R xl s l
l Ff r e q
{[,4Hz)
3766
3767
370B
3/ 70
3tì1
3l i2
3/ 73
3i Ì5
3 77 6
3Ì11
3778
3780
37Bt
3782
3783
3785
3786
3787
3788
37S0
37.91
3i 92
3795
3793
3794
37.96
3797
3798
3799
3800
3 80 1
3802
3803
3804
3805
3806
3807
3808
3809

l CP r o q r aPmr sn

0

l

l

0
0

0
0
l

u
I
1
0
I
0
l
0
1
1
0
1

0
IJ
l
0
1

0
0
0
0
0
0
0
0
0

I

U
0
1
0
0

0
0
0
0
0

l
l

U
l
I

0
l
I
0
0

0
0
0
0
0
0
0

l

1
0
0
l
0
I
0
l
0
I
0
1
0
t
0

0
0
0
l
l
0
1
l
O
0
1
l
U
0
l
l
0
0

l

l

0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0

U
0
i-l

0
0
0
U
0
1

U
0
0
l

ó
0
0
0
0
0
0
ó
0
0
0
0
0
0
0
0
0
0
0
0
U
0

ó
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

N O T E S1: ) H I G H L e v e l( ' 1 " \ = 4 . 5t o 5 . 5V D C ;L O W L e v e l( " 0 " ) G N D .
y i r e dH I G H & L O W r e s p e c t i v e fl yo r a l l 4 0 c h a n n e l s
2 ) P i n s7 & 8 p e r m a n e n t lw
a n d a r e o f t e n n o t e v e ns h o w n i n t h e T B U T H C H A B T .
3 ) A u s t r a l i a 1n 8C h a n n erl i g f r e q u e n c i easr eU . S .C h a n n e5l Î o U . S .C h a n n e l 2 2

- 3l-r-

called a "Truth Chart".
How exactìy was the numbcr ,,880,,
decided?Chart 2 shows the truth
states for Channel I only.
Above;."h
;ji;o;".u_
or., are numbers
l've labelled .,POWERSOF
2,,,such as t, 2, +, g ,ip to ZSObecause
this is

;í"* "pth" * uighr-oi
:àT?i"
*"": ;,iHy,ir' :.îl :;;;i:' É;;"d
rermined.rîr,"1.ò;ii"."11":fl";;,L;l;"xr,r,"""iì;.,i,.

256+64* 8 +2 - 3J0.Fieurer l"h;;;'til;

lî:"iff}" :[i#il"Í^"'

channer
1 Binaryproeram.,"n
""f
= N

";íri'#r,u""

".*itching.Try
"r'"'""r""vJ'..irr,
r"",, beusing
rhis

l,tÎlo;o

^, synthesizer
Described
in rexr

3 3 0 :2 S 6 , sb i t + 6 4 , sb i t * 8 , s b i t +
2,sbit = 330

P O W E R SO F 2
PLL PROGRAM
PIN NUMBER
IRUTH STAIE,
C H A N N E L1

2

8

to

32

64

11

10

9

I

7

0

0

1

0

1

t3

14

13

12

0

1

0

'|

"1" . +4-B
V D C ;, ' 0 ,=, 0 v D C

128

256

orcround.

Notice from Chart I and Figure
1l.that the logic sratesof pins Z and g
never change at all for
th" 40 ;ir;;;;is. Instead they are
permanently hard-wired ?"y,of
to-the chassis """'fr^tfr.t pin Z is
always
connectedto +DC voltage(,,r,,)
""J pi" À;;*"y.
grounded(,,0,,).
_36_

a

I

À-

rws the truth
are numbers
:causethis is
re weight or
-Code is derple,we have
ritching. Try
e using this

I"IGURE 11, HOW THE BINARY N-CODE IS GENERATED

tr28ì f256t

o

P LL O 2 A
l32l

t16t

l8l

14ì

t2l

trl

b e di n T e x t

J

I
\

I

to +VOC

\
Part of C hannel
Parl
Selector Swilch

pins 7 and 8
ad they are
7 is always
unded("0").

-; N = 256 bit + 64 bit + 8 bil + 2 bit = 330lor Channel1

-37 -

You'll discoverthat many servicemanuals
won,t even indicate these
pin states in their Truth Charts b""u,r."
th"V ,r"rr", change uhen
programming the leeal 40 channels
only. This is-acaseof thoselnissinj
bJa.nkgI'm filling infor you, and you "à"
i""ltfri" idea by checking the
riB^'s.crrcritdiagram. Compare thó tot"t p.og.u--ing
pins available to
LrreruLal numoer used ln a 40_channel
rig; you,ll find an obvious
modification source!

The l8-ChannelAustralianCB servicewas recently
expandedlegalty
to match the standard 40-Channelf,CC a-ericà"
Australian rigs are simply U.S.rigs *ilÀìirff"i"nt sl.vice. Sirr"" riàr,v
(Ìimited)Channel
selectorswitch,they can beeasily"modìiì"ai" """".
ilre extra channeÌs.
For example,Australian Channel 1 t;-il.01b
MHz,
which is U.S.
Channel5. The N-Codehereis 325.The N-C;;
for
Australian
Ch. 1g
(27.225MHz) is 304.Therefor" Uv ,"prog.uÀriing
N_Codes
of an t8
clannel A"-qtratianrig for numbJr.
s;";;;;;;;;B2b
or
tess
than
304,
the rig can be
expanded.

This particular chip, the pLLO2A, has a total g
of binary programming
pins, which are pins 7 - lb. It tÍrerefore
fr". *irut,. called a ,,g_bit,,
binary programmer. Some quick math
wili t"tt vuu that this chip
actuaìlv has apotenfiar channercapab ityof
?-i, o.sr r "rru.rnersl(1+2+4+g+
16+lJ2+64
+128+256-. 511).Only-40 "hurr.r"l.
"* """a fo. Cg p,r.po.à.
but by proper connection and switchìnó
"i ""r."a pins, many more
frequenciesare possible.

VCf)CIRCUIT

Referback to Figure 10 on page 34.This
VCO runs in the 1?MHz range,
going from tT.ISMHzon Chànnel
t to ú.AbMÉ; o" Channel 40. The
vco is controlled by an
voltage
it ,ecei'es from the phase
-error
Detector, which is always_looking
i"ii -rt"ii"r*"".,
the Reference
Divider and program-àut"- oirria-";;J;;.îh;
ReferenceDivider is
-MHz
v.ery
Sccurately controlred by a 10.240
crystar osc rato. *hose
signal is divided down digitaily by f
,OZ+t" pr"a"'ce the 10 KHz channel
spacrngs. If the Programmable Divider shóuld
Àiro h.pp"., to;;;;;;;
an exact 10 KHz output, the result would
be pàrfecf;^there,à U"ì"
correction from the phase Detector, and
the loof wouÌd be locked.
-38-

Whe
I'r'o
l)ir.

s(,e.
t ( ' sL
Srrìl

l r e rt

Lf)t]P

I l sc
s()tn
I)iv
rvill
loop

r7 .

'l l)'rhoec

ispr
MHr
srf{n
26.9
firs t

PHA

Wha
I)ivi
any
d i f'fe
; t .I ( )
be il.
this
colr(

(ì()n s
occu
thev
I to (

BEC

This

dicate these
nnge when
Lose
missing
hecking the
availabÌeto
an obvious

What would it take to produce a perfect 10 KHz output from the
Programmable Divider? We've already seen that the Programmabìe
I)ivider is set to divide any signal it seesby the number 330.Ifit should
see,fbr example, a signal of exactly 3.30MHz appearing at its input, the
r e s u l t i n g o u t p u t w o u ì d b e1 0 K H z . ( 3 . 3 0 M H 2 . 3 3 0= 1 0 K H z . )I f w e c a n
somehow produce an input signal of 3.30 MHz, everything wiÌÌ falì
perfectly into placel

LO()P
MIXII{G
rded legally
Sincemany
ed)Channel
rachannels.
rich is U.S.
rÌian Ch. 18
les of an 18
ss than 304,

ogrammrng
ed a "9-bit"
rt this chip
:ls!(1+2+4+$+
)B purposes
many more

MHz range,
nneì40.The
r the Phase
reReference
:e Divider is
lator whose
lHz channel
n to produce
rere'dbe no
Ìocked.

It so htippens there's a very easy way to do this by cleverly borrowing
some existing circuitry. If some 10.240MHz energy from the Reference
L)ivider is taken off and passedthrough a tuned doubler stage, the result
will be 2 x 10.240MHz = 20.480MHz. Here'swhere that very important
loop mixing principle enters:By mixing the 20.480MHz signal with the
17.18MHz Channel 1 VCO signal, sum and differencefrequenciesare
produced.Th e sum frequencyis 20.480MHz + 17.l8 MH z = 37.660M Hz.
The differencefrequencyis 20.480MHz - 17.18MHz = 3.30MHz which
is preciselywhat's neededto lock the loop on Channel l. And the 37.660
MHz signal isn't wasted either; it's used as the high-side injection
signal to produce the first receiver IF when mixed with the incoming
26.965MHz Channel 1 signal. (37.660MHz - 26.965MHz - 10.695MHz
first IF).

PHASE
I]ETECTOR
Cf)RRECTIflT{
What happens if the mixing product entering the Programmable
Divider isn't exactly 3.30MHz? Think about it. Sincethe N-Codeis 330,
any signal other than precisely 3.30 MHz will produce a slightly
different output to the Phase Detector. For example, if a signal of only
3.10MHz entersthe ProgrammableDivider, the resulting output would
be 3.10MHz -: 330 = 9.39393KHz. The Phase Detectorwill now sense
this error and try to correct it by sending a DC voltage to the VCO. This
correctionvoltage will drive the VCO up or down slightly in frequency,
constantly being compared in the Phase Detector, until an exact match
occursonceagain. Aìthough this appears to be a trial-and-error process,
the whole thing happens in the time it takes you to switch from Channel
1to Channel2!

R E C E IlVFEs B
This completes the basic loop; everything else is icing on the cake.
-39-

lu*.t1." ChannelI

pl-r, mixersrgnatof

32.660
MHz
j
Il
n
e
cti
o
n
sì;;

N;
;
"il:
ilffi
ffi :
i;T*"":*':":l:::' :.rll'l
it.
"
il'
;il'ì
;;ff
il.i;?#riiil::
àt"
11:l::r..:1lr:d'r,"
:3".
T;;
";
j"*,,,i,"jilT;;
j1t|: 1ò-6ebffi "'ii."i in",",l
$';1,1 Bl,iì )ljy i,y_i
Y"::Xl:|1"

ssr È,,tr,i.* ;;î'ili iil i'::î1XTíli
yI:--.a
""ìîfi.8H": ::
I* ;,T "r-1_r..
theseengrneers
I AImosr "r\ir;
",':*

J:
;;
;
;,
;;;
;;;;;"
i;:J
;
;'fi:
fi ff :::
l|::*":i.::::::"':t
FMY"i
stere.s,
etc.where
o tutolt'#;::#i*àl":î:
lf,i".::l;ì T:111_:y"

li"1*:,"-T1.1"j,s,
already
existed.

l
I
i

(

TRAIISMITTER
SECTIf)I{

)

i

(

For the transmitter of
the on_channel frequtncy is
'";;;.;;
.this example,
produced verv simolv..rrv
,"l"irrg'"
10.695 MHz crvstal
osciÌtatorwith the

si._ooò
un, ir,À"""íìì;Lr
mixer ourput.rhe
difference
is 32.660
M\"
ió.às5
ùri;:
zi.iàs
ruur,
whichis rhen
.
tn-""h tunedcircuir,
u",l ;Ì,;;;.-liiiu.,._itter
RF.amplifier
:ff:;l
You can usethe preceedingexplanation
as the basrsfbr an-vpJ,L circuit
you find. We'veaÌreadv r,gu.àa
;r;;;;;;;;;lho.,
"o__nn ones for
you and their block diagrams
appear in SectionlII.

I

(

I

E

f

t

f
d
f
c
c

TRUTH
CHARTS
& PB{]GRAMMII{G
METH()IIS
IIi flETAIL
1'he'lruth Chart is the most important
first step rn determining how a
modification can be macìe,or even
r/it can be màcle,so we,ll look at it in
greater detail now_

B

A
'.

The example just expìained was
a
eas.ylrl,L circuit using the
Drnary type of programming c.de. .very
rt'" quit" f...Ìure lor the same chip
to have different N-Codesriep""air_rg
upàr, fr-uinì
many crystals are used.
whether ifs AM or AM/SSÉ,
"t". i'f,"ìira zl".n"r"f loop had N_Codes
gorng from 330 down to 2g6,
becaus.trr""" *"r" irre diviciers needed
for
proper loop mixins. An
earlier pl-ió2i' ;;l;_e
used
a
B_crystal
svnthesizer with Nllodes
eoi.'e t o^iiiir,ì.}rs.
And for the ever_
popular PLLO2A SSB chas-sis
ia_"r1"", ;; ;"u;oo".r, versions), the
N-Codesare 2bb down to 211.
Notice that theseN-Codesmay go
up or down with increasing channel
-40-

(l

p
ri
el

tt

in
1
sI
e)

pr
th

37.660MHz
from Figure
[z Reference
rult is 10.695
n product is
FM CBs use
usedin car
it hardq'are

requencyis
{Hz t:rystal
output. The
hich is then
ìF amplifier

'PLL circuit
nononesfor

number; this depends purely on the VCO's design. In Section III you
can compare all the PLLO2A block diagtams to see where and why
these differences occur.

Meanwhile let's return to a portion of Chart 1to study some of its other
features. Chart 3 shows only the channel number, channel frequency,
and N-Codes from the original chart. Observe the progression of NCodes from Channel 1to Channel 40. Notice anything unusual? ?àe
N-Codes are not all consecutiueand skíp afew numbers any time there
is no legal CB frequency. For example, Channel 3 is 26.985MHz, and
Channel 4 is 27.005MHz. What happened to 26.995MHz? It's not a
ìegally assigned channel. This is known to CB people as an "A"
channel, in this caseChannel 3A. There are also skips at channeìs 7, 11,
15,and 19.In addition the American FCC Chann els 23,24,and 25 are
assigned out of order. Therefore all N-Codes as well as VCO and mixer
frequenciesare also out oforder in the chart. Many European countries
having only 22 channels simpÌy adopted the American scheme exactly
for the fírst 22 channels. Australia uses 18 channels whose numbers
didn't correspond to American,zEEC numbers but many of the actual
frequencies are the same. And Britain originally used 40 consecutive
channels having no skips at all. Remember this fact whenever you're
checking a PLL Truth Chart; otherwise you might think your math is
wrong when it isn't!

BCO
PROGRAMMING
.ininghow a
I look at it in

it using the
resamechip
als areused,
radN-Codes
's neededfor
a 3-crystal
for the ever-'rsions),the

ing channel

Another common programming method is called "BCD", which means
"Binary-Coded
Decimal". Think of it as a cross between the binary
(Base2) and human Decimaì (Base10)number systems.Chart 4 shows
part ofa BCD channel program used in the very popular uPD858SSB
rigs. (Eg,Cobra 138,2139XLR,
Realistic TRC 457/ 4í8,Prcsident "Adams",
etc.)This chassis is an older PLL circuit requiring a Down Mixer into
the Programmable Divider. If you check the block diagram for this chip
in SectionIII, you'll seethat the downmix frequenciesare .910MHz to
1.35MHz. Therefore the N-Codes are 91 to 135 for standard 10 KHz
spacings. Note that the N-Code between channels 3 and 4 skips in
exactly the same way as in the PLLO2A circuit, since Channel 3.,A.
is not
a legal CB channel. What's the big difference? Above each PLL
program pin number is now something called "BCD POWERS" rather
than the previous "POWERS OF 2".

-4r-

C H A R T3
N - C o d e V a r Ì a t i o n sF o r C h a n n e t
Asstgnnìents

( , n an l l e t
l
2

:
J

5
6
8
9
t0
ll

12
13
1,1

15
t6
1i
]B
l9
20
21
22
23
21
25
2î,
2i
2B
29
30
3l
32
33
31
35
36
37
3B
39

Charìr]e

26965
26975
26985
2i 005
2i015
2t-A25
2i 035
2/ 055
2t 065
2i 0t5
2i 085
2t 1Ds
2i 115
2t- 125
2 71 6 5
2 71 ì 5
2i 185
2t 2A5
2ì 225
2t255
2t 235
2i 215
2i 265
2ì 2ì5
27285
27295
27305
27315
2i 325
27335
2/ 355
2/ 365
2i 3ì5
2/ 385
2/ 395

N d r qI a l

330
329
328
326
325
324
32J
321
320
319
318
316
315
Jrl
J13
3 t1
3ltl
3{19
308
306
305
301
301
303
302
3Lì|]
299
298
297
296
295
294
293
29?
291
2911
289
2BB
2Bì

C H A R T4
B C D P r o g r a m m i nogf u P D 8 5 8C h i p D e s c r i b e idn f e x t
(}nes
BCDPOW
ERS
PLLPROG
BANl
PINNUIVIBER
lh

l

) h 2

91
92

2
I J

0
0

4

I

10 20

t3

to

17

0
0
0

0
0
0

20

21

22

0

0

0

0

0
0

0

0

0
0
0
0

0

1

0

4

0

1

0

lh 40

135

0

1

0

1

lh

80 100 200

0
0
0
0

J

40

18

9J
95

lh

llundreds

Tens

0

N O T E P n 2 2 p e r m a n e n ty . l r o ! n d e d t o c h a s s r s( ' 0 ) f o r a 4 0 c h a n n e l s

In this system, the pins have been assignedsuch that each successive
group of pins has a weight or significance 10 times greater than the
preceedinggroup. Within each decimal group, weights stilÌ double in
the usual binary progression,exceptthat the highest possiblenumber
in any group can't exceed9 or its decimal muìtiple, such as 90, 900,etc.
(Assuming there were that many pins on the chip.)Each decimal group
can only have a maximum of 4 bits; in this chip, there are only l0rather
than 12programming pins so the Hundreds Group can only add up to a
maximum of (t + 2) x 100 - 300. Figure the total binary value in each
group, multiply it by 1, 10,or 100 as appropriate, and add the groups
together:Ones Group + Tens Group + Hundreds Group, etc.
Since each group has a value, the sum of the groups produces the
N-Code.For Channel 1, we thereforeget 1 + (10 + 80) = 91.Try the math
yourself for the other pins. Notice also that pin 22 is permanently
grounded, since its weight is "200" and vre never need an N-Code
(100+ 30 + 5 - 135).By using alì 10 programming pins
bigger than 1115.
(pins 13 to 22) there's a potential channel capacity of9 + 90 + 300 = 399
channelsif N-Codescould be programmed from 1 to 399.This fact has
been put to much use in frequency modifications! Once again, the 858
chip has this excess capability for possibÌe use in other synthesizer
circuits besidesCBs.
Beforeyou get too excited about all the potential channels hidden inside
somePLL chips, I must point out that most rigs can't possibly cover as
wide a range as these chips without a lot of retuning. Modern rigs are
capableof about 1.2MHz to 1.8MHz total bandwidth, which means 120
to 180 l0 KHz AM,TFM CB channels.
-43-

The BCD method was originally used in about ll%t of the older
generation circuits. The reason was becausecertain support hardware
s.uch_as BCD switches, keyboard controllers, and i-Àegment LEf)
displays required BCD inputs. The current generation alÀost .l*ry"
usesBCD inputs. Someexamplesare the LC7l2O,LC7lB0/Bl,LCZldb,
LC7136/37, uPD28t4, uPD2816,and upD2g24..ih""" chips aÌso onìy
have 6 programming pins.

P R E S E T TtAl IEVLI O
E EBS
An interesting variation of the programming expansionschemeis used
in the new Cobra 148GTL-DX,which is a very popular rig soìd only in
Europe and the U.K. In order to get f 20 channels,they sta.t off*ithih"
same very flexible chip, the MCl4b106, as usedin the typical PLLO2A
chassis. Only this time, the N-Codescan be preset to a new set of 40
channels each time you changethe L,M,H band switch. This is done by
usin g-two special digital counter chips, the MC 1400gs,wired such thai
each band selectionalso changes thè set of N-codes.The net resuìt is
that a single Loop Mixer crystal ( 1b.00MHz) can be usedto provide 120
channels. In previous 80 or 120 channel schemes. additional looo
mixing crystals are switched in while maintaining a single set of
N-Codesall the time.
The reason for doing this is purely economic: The Cobra 148GTL-DX
can offer 120 AM/FM/SSB channels, and a dual_conversion AM
receiver, for a total ofonly BcrystaÌs in the whole radio. Compare this to
the typical 120-channelCybernet (Ham Int'Ì, Colt, Major, etc.)or the
120 channel Uniden Superstar 860,which require b anà 6crystals re_
spectively. The cost of a crystaì to the manufàcturer is aboui
$B each,
while the costof two MC 14008sis about g1 total. Sincethereis roughly a
5:1 mark-up from manufacturer's cost to actual retail price of a ri!, túis
means a savlngs to you of 930 to $45 on the totaì retail pricel

c
I



1

t

L

1

e

li
b
L'

u

c

E
b

A

n
c.

it

b

c
Y

C(

The idea ofpresettable dividers is also found in several other pLL chips.
The most common example is the MBg719. While the chip at first
lpp"ql" to have 7 binary programming pins, closer study shows that
Pin 10is actually used to presetdif f er"rrl N-cod"" for use with different
loop mixer crystals in the American rig versions. (11.112bMHz vs.
_lJq?58MHz crystal in an otherwiseidentical chassis.)In the newest
Il:9_"1_Eulgpean rigs (Eg, Statker ST9F-DX, Superstar B60FM) rhe
MB8719 or MC145106chip is usedalong with the MC14008presetíabre
dividers to provide 80 or 120channels. In the Stalker, they even provide
an additional Loop Mixer osci ator on its own smarì pc boarà which
can be switched in to give the 40 U.K. channels as weÌÌ. (15.4g25MHz for
the first 80 "FCC" channels, and tb.bb62b MHz for the 40 U.K.
-44-

sl

dr
r€
tl

('(

tn

th
IS

hr


SC

I the older
t hardware
ment LED
ost always
11,LC7135,
s also only

channels.) Of course the N-Codes are different for each band and the
Band Selector switches both the crystals and the proper IC programming at the same time.

MULTIMl)flE
PRÍ)GRAMMIT{G
There's one chip that deservesspecial mention, even though it's not
being used much anymore: the uPD861. NEC really outsmarted
themseÌves with this one!

emeis used
;oldoniy in
off with the
al PLLO2A
rw set of 40
s is doneby
rdsuchthat
ret result is
provide120
tional loop
ryle set of

I48GTL.DX
ersion AM
rparethis to
etc.)or the
crystals rerut $3 each,
is roughly a
rf a rig, this
:e!
'PLL chips.
hip at first
shows that
th different
25 MHz vs.
the newest
360FM) the
presettable
ven provide
oard which
325MHz for
he 40 U.K.

The 861 has some special controÌ pins so that the designercan choose
either binary or BCD programming. There are 8 binary programming
lines, which means a possible2s-l or 255 channels when used in the
binary mode. In the BCD mode, a special "ROM" Code Converter is
connectedto allow only the legaÌ 40 channels. Thus the 861 could be
used in other synthesizer applications. In Section III you'lÌ find the
exact specs;note that simply changing the voltages on a couple of
control pins wiÌl allow you to convert a rig which when used in the
BCD/ROM mode is non-modifiable. You can then program it directly in
binary with switches.
A few chips such as the uPD2810, uPD2814, and uPD2816 allow
multiple choices of N-Code sets such that several possible downmixer
circuits can be used.This feature is intended only for design flexibility;
it won't help you in your modification attempts. (Actually the feature
was intended to make the chip usable in both AM,zFM and SSB circuits,
but to date only the AM/FM design has been found in CB rigs.)

C()NTRflLLII{G
PRÍ)GRAM
PII{S
You know that to controì a program pin, a voltage or ground must be
connectedto that pin. Most chips have resistors built into the chip
structure which are connected internally to the main +DC supply or
ground pins ofthe chip. Theseresistorsare caÌled "pull-up" and "puÌldown" as they automatically force the logic state to
respectively, unless controlled externally. The external control takes
the form ofthe Channel Selectorswitch if the pin is needed,or a direct
connectionto the rig's circuit board ground or +DC ifnot neededfor only
a 4O-channelset of N-Codes. When you need to control a pin for
modifications, cut the circuit board trace leading to that pin and bridge
the cut rvith a small (7+watt) resistor of about 1K to 4.7K ohms. This will
isolate that pin until it's ready to be switched by you. In addition it can
help protect the chip from possibledamage due to static electricity; a pin
shouÌd never be left "floating" and should always be connected to
somethingexternally.
-45-

Returning to our first example,
the pLLO2A has internaì puìì_down
resrstors,which means that eàch prog.uÀ
pi" i"'"1*ays i;ih;;ò;, s;;;;
until +DC is applied externarrv.
Sà iriour.i"àiii""ti""
cails fcrrcontrol
ofsay' Pin 7, cut the fo tracegoing pin
to
7
and
bridge
it
with a resistor.
Figure

t2 showsthe orincipie;i'.;;;;i
iiiio.,t.or; it,s commonly
usedwith the pLLO2A.n4e'8fr9, ;àìpfrA'#'"hro".
you can alsouse

this idea to get the auíom.atic
C.h.g/lg.""uif

fuuru." in the LC7131,

L,C7rB6/s7
"tu".i. lr"ir," ,ìà-i*.",t
k:l"tt,:à.".

atreadyhave ii

R()M
PR(]GRAM
C()DE
CONVERTEBS
'Ihe

reason the newest:l,l_,. ".:î BCD
programmrng ìs purely a legal
one:By using BCD combinedwith
a
sneakyldditionut
circuit insicrethe
chip catled "RoM,,, any iilegaif;;q;;;;;fi;ficarions
by changing
programming voltages
now impossible. .fhe current F.CC
.are
rules
require that the pLL chip can
only ";;;;'"
àtal of 6 programming

pins. So even by usine ihe .t."r*í,r"[ìiil:r;;-,
this aìone limits
possiblechannelsto zs_t, ".
OSlg_t"f"f,"";"ì:. ii + 2 + 4 +8 + l6 + 32 =
63.) By c-ombiningBCD and ROM,
;;;';iii'r,r_rr".
is reducertro
exactly 40,22,or lg as the casemay
be for variouscountries.
lr_

d*î, the British government has given
their ,,CB 27/g1,, approvai

iiisi,i;;ilji?"Hi'.},".:,,ryJ:.tx,:;[:1
ii1i,,f"""*:ru:,*::.",*::Í:*'lii
&tì?ìi':.i,:ifi
c h a s s i os r r h e . T C e t r g
u ' i a u i " r , 1 " r i i . ì ; ' i ; ; ' i ; S . . t h eo n l yr i g s
sri'

".xl&"4llrlff
ilxx'-ff
t,Hi*,i.;
#JrdlL'"':l;ilifr
;'"':ffi
*i:i:.'.,.".ffi
d+tli'i*:;l;T
"ut".*iuaroi;;;#;r"Hillit"":"j#*+:i,{ef
when
rheword
gers
"rr.iit#""liiaxXl.rXT;
::::i,".x*;::i,nm;
llt:lîjjlnihilim,
ii#"T,",yùrnce governments finally got
wise to all the boo eg OB frequencies
b e r n gu s e d ,R O M w a s t h e a n s w e r .
A . , R O M C o d eU o n v e r t e r , , i n s i c lae
tl]r is-the-kev to preventing
modifications. ,I.he rerm ,,ROM,,
ILL
means "Read Only Memory',
" "."a i" digitaÌ computer
^u"di;;;;"f
systems. Inside the chip, safety
""r;i;;;;'ti;;;"",
is a RoM Code
_46_

I

i
t
^\_


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