6m Surprises

One of the cool things about working for RFC is getting to go to some interesting ham get-togethers. One of my favorites is the (by invitation only) 6m barbeque, held in Texas each fall by Dick, K5AND and Jimmy, W6JKV.

Each year I go I find out something interesting about the "magic band", and about the fabled hospitality of Texans. This year was no exception, and what I learned has a tie-in to high power amplifiers.

Jim Kennedy, K6MIO, and Gene Zimmerman, W3ZZ, gave a really riveting paper on two interesting 6m propagation modes that they have described and for which they have proposed possible explanations. These occurred at times and over propagation paths that were unexpected.

One of the fascinating (and sometimes confusing) things about 6m is the sheer number and variety of propagation modes. This is due to 6m being located at the crossroads between HF and VHF. It is the lowest frequency band at which moonbounce is commonly done; and it is normally the highest band which sees any significant F-layer propagation near sunspot maximum. There is also summer sporadic E (Es) propagation, in which signals bounce off "clouds" of ionization that appear, move around and disappear, sometimes surprisingly quickly. This can be extended to multi-hop Es where there are clouds situated such that two or more hops can be achieved to give extended range. This happens fairly often from here in Colorado looking East- one hop puts us in the Midwest, two on the East Coast. When this happens, the two-hop signals are almost always weaker than the one hop. On much rarer occasions, we hear three or four hops into the Caribbean or other islands. These are weaker still, and it really helps to have a good antenna and as much transmitter power as possible to work over these paths. Working PJ6 from here took hours, and they came above the noise for only 30 seconds or so - I joke that it took every watt of my skill.... I often wonder if there were more QRO 6m stations down in the Caribbean if this propagation would be seen to be more common than we think. Apart from the summer Es, there is occasional winter Es, which really is exciting when it occurs. Mostly Es is a mid-latitude phenomenon - the closer to the equator or the poles, the rarer it becomes.

Back to Gene and Jim's paper. They have analyzed two kinds of extremely long distance 6m propagation that occurred recently and have suggested new names for them, to add to the already rich alphabet soup for 6m. The great thing about what they have done is that they used a new "data driven" model of the ionosphere that gives the ability to "see" using a computer what actually happened in the ionosphere at some time in the past. This allowed them to come up with plausible physical explanations for these modes, and also suggests that they may not be "one off" freak happenings.

Figure 1 - NA-Scandinavia EWEE

The first is one they call "East-West Extreme-E skip" or EWEE. This occurs in the summer between stations in the same hemisphere. Actual examples of this are given in Figure 1 (Western US to Scandinavia) and Figure 2 (Western US to JA). The underlying ionospheric physics behind these is somewhat tricky, but these paths are basically probably triple-hop Es paths, at a much higher latitude (close to polar!) than would normally be associated with Es.

The other one they described is called "Transequatorial Es-F-Es". This was typified this past winter by some literally jaw-dropping QSOs between stations in the US and VK and ZL. I remember staring in disbelief at the realtime NA map on DX Sherlock, and seeing a bunch of lines heading off over the Pacific. At first I wondered if moonbounce had overnight become more popular that I had thought. That would have been amazing, for sure, but it soon became apparent that something even more interesting was going on. The paths for this are shown in Figure 3. As for the EWEE above, not all the QSOs that occurred are shown, just some representative ones that they analyzed in detail. In both cases, there were many more stations involved. These are paths of the order of 10,000-15,000 km! The path existed for a period of some hours. This would have been a fun opening on any HF band, let alone 6m.

Figure 3 - NA-VK/ZL TEFE

The explanation Jim and Gene give for this "TEFE" mode is that the signal starts off with a couple of Es hops, then makes a single hop off the northern F-layer equatorial anomaly to cross the magnetic equator, and then finishes its trip with more Es hops. This requires a lot of things to line up in order for it to happen. There must be ionization clouds in both hemispheres suitable for Es- winter Es in the Northern hemisphere, and summer Es in the Southern hemisphere. And the ionization above the geomagnetic equator must be suitable for TEP (Trans-Equatorial Propagation) at 50 MHz. The plausible hops for this can be seen in Figure 4.

Figure 4 - Plausible hops for TEP

So much for a dead band in winter! Or having to wait for F2 propagation near sunspot maximum in order to work the other side of the world. I was wondering why this had not been noticed before, and I have a few ideas. First is the fact that 50 MHz was not a permitted ham band in many countries until quite recently, due to low-band television. The second reason is that good radios with 6m have only comparatively recently become the norm rather than the exception. There are also now more really excellent antennas than before, many of them computer-optimized and capable of taking high power.

Figure 5 - Transequatorial EFE  

But the final element is the availability of high power linears, such as the Alpha 8406. So assembling a high-radiated-power station to take advantage of these paths, where each hop makes the signal weaker is now easier than ever before. This makes it possible for anyone to participate in some the "magic band" happenings quite easily - your rig probably already has 6m. Get the biggest antenna you can, and add an 8406. If there are enough QRO 6m stations, maybe we would discover that these "exotic" openings are lurking there, below the threshold of what can be worked with less power. As Werner von Braun said "I have learned to use the word "impossible" with the greatest of caution".

All figures in this article were kindly provided by K6MIO and W3ZZ, and all rights rest with them.

73, Gordon, W0RUN 

As you can imagine, we are very busy here trying to put all the pieces into place to ship the amplifiers that many of you bought in order to take advantage of our October promotion. Purchasing, Production, and the Technical staff are all kicking into high gear to ensure that we have the parts and equipment necessary to fulfill this demand.

Our Purchasing Agent here at RF Concepts is Carey Fuller, KX0R. Many of you speak on the phone to Carey from time to time; he has been with the company for over three years and is primarily devoted to purchasing right now, although he has filled a technical role in the past and sometimes issues RA paperwork for repair items. Carey is an active ham and you might find him in the backcountry for Field Day, operating all by his lonesome which is the way he likes it. These days he is running around with his hair on fire, keeping track of inventory and trying to ensure that we get parts in neither too early nor too late, but just in time.

Thanks to all of you for your orders. We are having some fun now!

73, Kathy, KB2HDT