DX RX

The Doctor of DX prescribes the
answers to your problems, low and
high, near and far.

A how to of what for, by Mike(aka Billy)Graham, K7CTW

PROPAGATION

On more than one occasion, I've been known to spout the expletive "Think Sunspots!" Put more accurately, sunspots are the "engine" which powers the phenomena of RF propagation.

From a physics perspective, propagation is defined as “to move through a medium”, such as a radio wave moving through the “medium” of the ionosphere. In its simplest form, radio wave propagation is divided into three areas: 1) Ground Wave, 2) Space Wave, and 3) Sky Wave. Ground Wave propagation is vitally important at Very Low (VLF), Low (LF) and Medium (MF) frequencies. In the HF spectrum (3-30 MHz), Sky Wave propagation plays the most important role, and at VHF/UHF and microwave frequencies Space Wave propagation is key. However, as in anything, there are exceptions to all the rules. The manner in which these varying aspects of radio wave propagation behave, is, in large measure, dependent upon time; time of day, time of year, and time of sunspot cycle. If this last statement were, in the strictest sense, 100% true, then forecasting band conditions between any two points on the face of the earth would be a “piece of cake”. But Mother Nature enjoys throwing curve balls at us.

Since the sun controls propagation of RF energy, at least within the confines of Mother Earth, it behooves us to pay close attention to “Old Sol”. While we can speak in general terms about the conditions noted above, it is almost impossible to predict, at any given moment, the sun’s surface activity, which is the engine of the propagation phenomenon. While avid HF DX’ers pray for sunspots, avid low band DX’ers (40 Meters and below) relish the “quiet” times of the sunspot cycle, and VHF/UHF enthusiasts love to see flares, aurora activity and other astronomical activities which aid them in their pursuits. Daily measurements of the Solar Flux Index, the ‘A’ Index and the ‘K’ Index provide the ham with a ready tool to determine the probability of successfully communicating on any given band at any given time period. The sunspot cycle is, on average, a period of about 11 years. The number of sunspots on the surface of the sun are, in general, related to the period of time within the cycle. If the number of sunspots were plotted along an 11-year timeline, a rough sine wave curve is created. This is illustrated below:

At the beginning of each cycle, surface activity is generally low, the number of sunspots is minimal, and Low Band DXing is the norm, with 20 Meters usually being about the highest band useable on a daily basis. Again, this does not always hold. During the last sunspot minimum a year or so ago, there continued to be considerable activity on 17 Meters. Four or five years into the cycle, the average number of sunspots on a daily basis peaks and communications on 15, 12, and 10 Meters is pipeline all over the world. As the cycle passes the peak and the number of sunspots (or the solar flux index) decreases, a gradual decrease in activity is noted on 10 Meters, followed by 12 and 15 Meters. This cycle of activity on the HF bands then repeats itself again.
The sun now is on the upswing of its 23rd cycle, a numbering scheme that dates from the mid-19th century, following introduction of the "relative sunspot number" by Rudolf Wolf of the Zurich Observatory in 1848. Wolf's sunspot number (now called the International sunspot number or the Zurich number) represents a blend of actual numbers of individual spots and numbers of groups of spots on the sun.
The current sunspot cycle will be above average but no record setter, according to scientists at NASA's Marshall Space Flight Center. Based on various precursor techniques, scientists there predict that Cycle 23 will rise faster than normal to its peak, attaining maximum amplitude sometime during the latter half of 1999 to the first half of 2000, and that it will measure about 170 plus or minus 20 units (yearly sunspot number). They expect Cycle 23 to continue until sometime in 2006 when the next cycle, Cycle 24, should begin.
The number of books written about the subject and art of RF propagation would fill a room (and then some, I suspect). John Devoldere (ON4UN) provides an excellent treatise on the subject of Low-Band propagation in his book “Low-Band DX’ing”. The ARRL Antenna Book provides an excellent introductory tutorial on the subject of RF propagation in general. This is “must” reading if your interests include DX or any other serious HF work. Other subjects include “Gray Line” propagation, Aurora work, Sporadic-E and the like. Additionally, WWV and WWVH transmit propagation data at 18 and 45 minutes after the hour, respectively. This data, together with other information which you provide, can be plugged into various Propagation software, now readily available, and the software will provide you with tables of information about present and projected conditions. Each month QST Magazine publishes charts of propagation predictions in the “How’s DX” column for a one month period. W1AW also broadcasts update bulletins. The DX Cluster packet network also provides access to these bulletins, as well as up-to-the-minute transmissions of solar data.
As if all of this were not enough, the Internet is crawling with sites devoted to the subject of Solar Physics and Propagation. A good place to start any investigation is AC6V's Gateway to DX and Ham Radio Web Pages at: http://www.ac6v.com/pageas.html. The site features 70 pages of its own on all amateur radio subjects as well as more than 2000 links to other sites. From there you can follow the links to the various sites featuring solar data, including extensive daily forecasting .

73 es Good DX, de K7CTW

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