Rick, > I completely accept that VHF SSB (which can also mean digital) > communication is really the only practical longer distance VHF mode that > works without infrastructure. But will we have a turn around in the > number of operators who actually use these modes? There is no question > that an increasing number of hams have the equipment now. But very few > are using them for 6 and 2 meter SSB. Fewer hams are operating weak > signal SSB, which has caused a significant drop in interest considering > that there are several times as many hams today than when this was much > more popular.
There are probably thousands of IC-706MKIIG's, IC-746's, FT-857's,FT-890's, or Kenwood TS-2000's in circulation that all have 2m SSB capability. Of course, it is sure that there are many more HT's and FM-only transceivers than those SSB transceivers. It is my understanding that weak signal operating is on the increase, mostly due to the introduction of WSJT, which is good, since the same digital interface can be used for 2m digital SSB. > > A local weak signal ham (50 miles north) said to me recently that years > ago (decade or more) there used to be many midwest U.S. stations on 2 > meter SSB, both fixed and mobile. But that is no longer true. And there > does not seem to be any improvement as of late. Maybe other areas are > seeing some increase? Don't know... Of course NBEMS on HF with NVIS antennas is still a viable alternative, but setting up point-to-point communications with EOC's on 2m is more reliable, and a 2m antenna, even a 10 foot long beam, is more portable than a long HF antenna for 80m or 40m. The advantage of medium range 2m (i.e. up to 100 miles) is that propagation is quite constant, whereas on 80m and 40m, it varies according to the time of day, and QRN can be distrupting to the ARQ transfer, slowing it down. There is little QRN (i.e. from static crashes) on 2m. > > But the unaswered question is, how much different would the path gain be > between horizontal and vertical polarization? And that might depend on > the distance since it seems that the farther out you go, perhaps the > horizontal polarization gives a slight edge. But really how much of an > edge? I guess only RCA knows, since they made the tests in the early days of TV. I wonder the same thing, and hope to find time to test, but just rotating an existing vertically polarized beam 90 degrees does the trick at no cost. > > Isn't it really the gain of the antenna over the polarization of the > antenna? Just because weak signal operators use horizontal does not mean > that emergency and local SSB operators need to do this. A local ham on our 2m net here designed and constructed a cycloid to see if random polarization was significant, and it turned out not to be. His work can be seen at KR1ST.com. Emergency and local SSB operators do not need to go horizontal, but if they do, then the existing weak signal operators can assist emcomm by being forwarding stations, and will have superior antenna gain to do that over longer distances. The antenna change from vertical to horizontal is much easier, and less expensive, than the change from FM-only to SSB. Perhaps a bigger problem is that many vertically-polarized beams are fixed in the direction of a desired repeater and do not have rotators. Once a rotator is added, it is easy to just rotate the beam 90 degrees at the same time. The catch-22 is that many of those 5-element beams are rear-mounted (to keep the metal mast out of the antenna field), and that puts an undesirable strain on a rotator, since it presents an unbalanced load, but it will probably not be a problem for a medium-duty rotator. Anyway, a non-metallic mast extension (like fiberglass) can be used to solve that problem and allow the beam to be center-mounted. > > We have many stations (most stations) that have gain on vertical and > nothing available on horizontal and never will have anything on > horizontal. Even hams who buy a multimode/multiband rig and now might > want to try SSB or digital are rarely buying a new beam just for 2 meter > SSB. Partly because of cost, partly because they can not due to local > restrictions, and partly because they often have upgraded and also want > to put energy into HF. They can just rotate the beam 90 degrees if they have a beam, but most probably do not, so they can just build the inexpensive design that will appear soon in QST, or use the latest three dipole "Big Wheel" in the March QST issue. The decision will depend upon how successful the ham is trying to use NBEMS or other messaging systems on HF with NVIS antennas compared to 2m. All my 2m antennas are in my attic (including my 13-element beam), due to restrictions barring outside antennas. The signals pass through the wood and shingles on 2m just fine, but there is some absorption on 70 cm. A 10-element 2m beam is around $100 and is the minimum amount of gain that should be considered. If one already has a multimode 2m transceiver, $100 for a good antenna for emcomm and general operating is not so expensive compared to $1000 for an SCS modem, good only for email and nothing else. For portable use, for $25, you can build a PVC and wire antenna that does not need a rotator and has the gain of a 5-element beam, good for a range of up to 50-100 miles, depending upon the height it is mounted. > > The other factor that seems to be in play, is that there does not seem > to be much correlation between hams who do weak signal and also do > public service, compared with the ham who is primarily involved in > public service and might add an new dimension to their operation if > asked to provide this needed service providing that they could use their > existing antenna or at least not have to have two separate antennas. The antenna issue is a minor one, if they already have a 2m multimode transceiver. A more compelling reason, in addition to public service, is exploring a whole new world of essentially QRM-free, long (up to 300 miles) distance digital and SSB phone communications. > > Consider the number of FM hams who have beams on vertical polarization > including fairly high gain antennas such as the double 13 element > Cushcrafts. Using vertical polarization, they can often use FM to access > repeaters from one side of our state to the other but unlike SSB they > can drop below the threshold at times as there can be QSB on these kinds > of signals. SSB would give them at least 6 dB or more margin and digital > should give quite a bit more. That is my experience over the past two years. PSK63 can provide 100% copy when you cannot even detect a SSB phone signal against the noise background. We tested PSK63 vs CW, and found CW was slightly better, because you can just detect the CW carrier modulating the noise background, whereas the warbling PSK63 signal cannot be heard, so you can find a weak CW signal when you cannot find a PSK63 signal in the noise. However, by "channelizing" (we coordinated by cell phone), once tuned to the same frequency, PSK63 and CW were very close in effectiveness. Of course, ham frequencies are not "channelized", so it is important to have enough gain to put the PSK63 signal far enough above the noise to be seen on the waterfall so you can tune it in. Once you achieve that (and every single dB helps!), the PSK63 signal generally gives low error-rate print. This is the case up to 100 miles or so. Over 100 miles, there is usually flutter or slow QSB, which will slow down the ARQ transfer, but few disasters span greater than 100 miles, and if they do, the alternative is somewhat slower ARQ transfers using HF and NVIS antennas. > > Your comment about PSK63 only working 50% of the time when you have > marginal phone communication makes me wonder if the digital modes are > able to work as deeply into the noise as claimed. Shouldn't there be > solid copy in PSK modes, even PSK250 or at least PSK125 at a few dB > below zero dB S/N? Phone communication, even SSB would need a bit over > zero dB wouldn't it? SSB phone has a average modulation percentage of around 30% without speech processing, and perhaps 50% with strong speech processing. In comparison, the duty cycle of PSK modes is near 90% (a fast string of exclamation points will show a continuous 90% duty cycle). This means that narrow band PSK modes, even without the benefit of sharp DSP filtering in the software, has a 2-3 dB advantage over SSB phone. Of course, "ARQ" on phone is harder to achieve than ARQ in a digital mode, only repeating a bad frame. The narrow bandwidth of the DSP filters in the software further increases the advantage of the PSK modes by cutting down the size of the noise window. To answer your question, our experience on VHF (where the background noise level tends to be constant), suggests that PSK31 does work under the noise level, but it does not seem to work as far down as Patrick finds, which is -11.5 db. We definitely see the 3 dB degredation going to PSK63, another 3 dB degredation going to PSK125, and another 3 dB going to PSK250, just as theory predicts, but in acual use, it really is hard to find a case where PSK63 has poorer print than PSK31. It is helpful to realize the importance of being able to work below the noise level. The big benefit is mostly on HF, where there is often deep QSB, so if you find a signal when it is above the noise on HF (it must be strong enough to be detected in the first place), and QSB sets in, the signal will keep printing even when the signal drops far under the noise level. That is the big advantage of the wider, multi-tone modes - the ability to handle QSB. Narrow PSK modes do just fine in the absence of QSB. However, on VHF, at distances needed for emcomm to reach outside connectivity (up to 100 miles), there is little or no QSB, so that any signal that can be tuned to (i.e. visible and contiguous) on the waterfall, will generally remain copiable, since there is little variation in signal strength. From 100 to 300 miles, there often is signal variation, but that is further than most emcomm situations need, and HF can be used in the few cases that it is, with slightly less throughput, depending upon the QRN level. I'd like to thank everyone on this list for letting us use the bandwidth to discuss these issues, and I hope they have been interesting and new issues for many list members, as they have been for me over the past several years. There really is an exciting new world on 2m SSB, both phone and digital, for anyone who has only used 2m to work repeaters, and it is well worth considering trying. It is not all "weak signal" work, either! 73, Skip KH6TY
