Regarding horizontal antennas... they also have a big advantage in rejecting intermod due to being cross-polarized with most commercial services...
--- In digitalradio@yahoogroups.com, Rick W <[EMAIL PROTECTED]> wrote: > > 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 > > > > >
