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popped up. While these have proven their use for predicting
propagation on the higher bands (the MUF-related bands), I
have never had any much use from then on the low bands,
certainly not on 160 meters.
In the world of commercial HF-broadcasting and HF­
point-to-point communications, the challenge consists in find­
ing the optimum frequency or maybe the best angle of radiation
(to select the right transmitting antenna) that will give the
most reliable propagation, as a function of the time of day. In
low-band DXing, the problem is quite different. The chal­
lenge is to determine the best time (month, day and hour) to
make a contact on a given (low-band) frequency, with a given
antenna setup, between two specific locations.
Cary Oler and Ted Cohen (N4XX) wrote in their excel­
lent article “The 160-Meter Band: An Enigma Shrouded in a
Mystery” (Ref 142): “Topband is one of the last frontiers for
radio propagation enthusiasts. It involves regions of the Earth’s
environment that are very difficult to explore and are poorly
understood. These factors have led to our failure to predict
propagation conditions with any level of accuracy. They also
account for our inability to explain some of the puzzling
mixtures of conditions that make this one of the most interest­
ing and volatile bands available to the Amateur service.”
Bill Tippett, W4ZV, hit the nail on the head when he
wrote: “If 160 were perfectly predictable, we would all
become bored with it and take up another hobby. Let’s just
enjoy it as it is because we’ll never be able to figure it out!” So,
don’t expect this chapter to predict all kind of exotic openings
on 160 for you!

auroral index, are updated every 15 minutes. An alarm can be
set up to notify you of a geomagnetic storm within a few
minutes after its start (Fig 1-1).
You can also view a Solar Terrestrial Activity report in
the form of a chart on www.dxlc.com/solar/. (See Fig 1-2.).
Fig 1-3 shows the progress of the present cycle (daily, monthly
and smoothed). The next solar minimum will likely occur
sometime in 2006 with Cycle 24 peaking in 2010. (See:
www.sec.noaa.gov/SolarCycle/ and www.wm7d.net/
hamradio/solar/index.shtml.) Note that the smoothed sun­
spot number in Cycle 19 peaked almost twice as high (200) as


Let’s have a look at the following time cycles:
The 11-Year Sunspot Cycle
The 27-Day Sun-Rotation Cycle
The Seasonal Cycle
The Time of Day

2.1. The Sunspot Cycle
It is well known that radio propagation by ionospheric
refraction is greatly influenced by the sunspot cycle. This is
simply because ionization is caused mainly by ultraviolet
(UV) radiation from the sun, and UV is highly dependent on
solar activity.
Solar activity can influence HF propagation in three
major areas:
• MUF (maximum usable frequency)
• Absorption from D-layer and E-layer
• The occurrence of magnetic disturbances
The sun’s activity is usually expressed in term of the
Smoothed Sunspot Number (SSN) or the Solar Flux Index
(SFI). You can get the SFI on WWV (eg, on 10 MHz), but if you
have a computer with a permanent connection to the Internet,
you can use a very nice program called IonoProbe, written by
VE3NEA. (See www.dxatlas.com/IonoProbe/). IonoProbe is
a 32-bit Windows application that monitors the space weather
parameters essential for HF radio, including SSN/SFI, Ap/Kp,
X-ray/Proton flux and auroral activity. IonoProbe downloads
near-real time satellite and ground-station data, stores that
information for future use and displays it in a user-friendly way.
Time-critical parameters, such as X-ray flux, proton flux and
Chapter 1



Fig 1-1—A number of ionospheric parameters can be dis­
played together, for a time frame of 1 day, 1 week or 1
year. For example, the Effective SSN, the Kp Index, Auroral
Activity, X-Ray Flux and Proton flux are shown here for the
last week. These are updated continuously using the
IonoProbe program by VE3NEA. (Courtesy of VE3NEA.)

2/17/2005, 2:39 PM