DX RXThe Doctor of DX prescribes the |  |
DX RXThe Doctor of DX prescribes the | |
From a Physics perspective, propagation is defined as “to move through a medium”, such as a radio wave moving through the “medium” of the atmosphere. In its simplest form, radio wave propagation is divided into three areas: Ground Wave, Space Wave, and Sky Wave. Ground wave propagation is important at VLF, LF and MF frequencies. In the HF spectrum (3-30 MHz) sky wave plays the most important role, and at VHF/UHF and above space wave 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 it’s not nice to fool with Mother Nature. She enjoys throwing curve balls at us. As you know, 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’ and ‘K’ Indices, 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, about 11 years. The number of spots on the surface of the sun is, in general, related to the period of time within the cycle. If the number of sunspots were plotted along a timeline, a rough sine wave results. At the beginning of each cycle, surface activity is generally low, the number of sunspots are minimal, and Low Band Dx’ing is the norm, with 20 meters usually the highest band useable on a daily basis. Again, this does not always hold. During this past year, there was considerable activity on 17 meters. Four or five years into the cycle, sunspots are at a peak and communications on 15, 12, and 10 meters is open all over the world. As the cycle passes peak and the number of sunspots decreases, a gradual decrease in activity is noted on 10 meters, followed by 12 and 15 meters. The cycle then repeats. The number of books written about the subject and science 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. This is “must” reading if your interests include DX or other serious HF work. Other subjects include “Gray Line” propagation, Aurora work, Sporadic-E and more. Additionally, WWV and WWVH transmit propagation data at 18 and 45 minutes after the hour, respectively. This data, together with other information can be plugged into various, readily available, propagation software, and will provide you with tables of information about present and projected conditions. Each month QST has charts of propagation predictions for the coming month in “How’s DX”. W1AW also broadcasts update bulletins, and the NE1V-5 PBBS retains these bulletins for several iterations. The DX Cluster packet network also provides access to these bulletins, as well as up-to- the-minute transmissions of solar data. These and other resources will be discussed in next month’s column in greater detail.
The topic of “Good Operating Practices” has kept writers and public speakers busy for years. I once spoke to NARC and four other New England ham clubs on the Ten Commandments of Good DX’ing. Likewise, all of us know, or should know, the common courtesies and practices which differentiate a real “pro” from the “LID”. However, each and every one of us, especially in the “heat of battle”, sometimes slips and says or does something which we know is not exactly on the up and up. Or we may just get careless. As careful as we try to be, we sometimes goof. I did just that.....I got careless and QRM’d a DXpedition, unintentional as it was. Believe me, my face was red for some time. It may be instructive to review a few of the more common practices and courtesies. These apply to all of us, not just DX’ers or contesters.
73 until next month de NE1V