Skip, Have you found that DominoEX is the best overall digital mode for FM? I know that PSK modes can have doppler errors from aircraft, but otherwise seem pretty good for weak signal.
Your point is well taken that many of the hams who participate in public service activities, may tend to be the younger ones who are Technician class and can mostly operate on 6 meters and up with their vertical antennas and FM only rigs. The number of hams with the multimode/multiband rigs is increasing, at least in our area. It is not easy to get them to try SSB, much less SSB digital though. The claim about the ground gain for horizontal antennas may be true but I have not seen this definitely tested. Have you done some comparisons with low 2 meter antennas, such a mobile to low base antenna with V and H and found H consistently better? I don't hold too much stock in software modeling and only would go with empirical data for that kind of test. We will probably bite the bullet eventually and put a rotor back up on the low tower and maybe go with a Gulf Alpha 11 element V and H antenna for some reasonable gain. Then we could do the test. The ham that was going to help us lost his QTH and will not be able to relocate his VHF antenna farm. Of course they are quite high so maybe there would not have been as much difference in such a case. One of the best known VHF ops in my Section says that after running many tests he has never found either polarization is any different. But he has high antennas so maybe that accounts for it. We hope at least soon do some digital mode comparisons on 2 meters, whether SSB or FM. 73, Rick, KV9U kh6ty wrote: > Hi Rick, > > Thank you for your comments on Howard's and my posts. > > Of course, we prefer using SSB on VHF, because the range is longer. First > tests indicate that DominoEX with SSB has at least a 3 dB advantage over > using FM with DominoEx. We are arranging more tests to be sure. > > However, the fact that today, maybe half of the U.S. amateurs hold only a > Technician license, and do not have access to full HF priviledges, together > with the fact that many hams only have inexpensive FM-only transceivers (but > only a relative few may have VHF or multimode 2m transceivers with SSB > capability), we have decide to explore ways that more hams can participate > in emcomm activities, which means finding out how to use FM-only > transceivers without repeater assistance. > > Although you have previously pointed out that many hams already have > vertical antennas, the fact remains that a vertical antenna close to the > ground (2 wavelengths), has about 6 dB less gain than the same antenna > horizontally polarized. At VHF, a 6 dB disadvantage is an enormous > disadvantage, plus many of the directive antennas used for FM are fixed on a > particular repeater, and cannot currently be rotated anyway. Just model a > vertically-polarized antenna over real ground at 2 wavelengths and compare > the gain to the same antenna rotated 90 degrees to horizontal polarization > to see the difference. In order to confirm Cebik's assertion about the gain > difference, I did the modeling myself and found that he is absolutely > correct. No difference in free space, but a huge difference over real > ground. > > So, putting it all together, we can get significantly more range by simply > investing in a horizontally-polarized antenna, using the same FM transceiver > that people already have, and, better yet, in an inexpensive TV antenna > rotator so we can communicate in any direction. The optimized two-element > quad that we used for the FM/DominoEx tests (7.5 dBi in free space) can be > built for less than $15 in an hour with all parts from Lowes, plus a SO-239 > connector, and turned with a $60 Philips TV antenna rotator from Walmart, > because its wind loading and boom length (13") is so small. A picture of the > little quad is here: http://home.comcast.net/~hteller/OptimizedQuad.jpg. It > is only 20" x 20" x 13", so it will fit in the trunk of a car without having > to be dismanteled. Construction uses schedule 40 PVC, fiberglass "driveway > markers" for spreaders, and #14 insulated house wire, so it is very rugged. > > I wish that all existing equipment could be used intead, but without a gain > antenna and horizontal polarization, range without repeater assistance > appears to be just too limited. > > It would be useful to know how much range you can get in your hilly rural > area by using FM, DominoEx, and horizontal antennas on 2m. > > 73, Skip KH6TY > NBEMS Development Team > >
