Paul, I use double or even triple diversity on 10m & 6m FM.
On 10m, I use a base-fed half-wave vertical installed right above & on the same mast as a 3-ele horizontally polarized 10m beam. That gives me rather more polarization than space diversity but it works FB. I have a 3rd identical rx as well, feed that with an HF longwire & ATU. One in a while, I get 2 different QSO's from the two rx's! What with FM rx capture effect (typically 6-8 dB), if one signal is 6-8 dB stronger on one receiver & another sig is 6-8 dB stronger on the other rx, that's what happens. Leo W0JZY in St. Louis, MO had a 10m FM repeater that used polarization diversity. And the same thing as I described above occurred. In 1980 Leo used signal strength to driver the rx voter for signal selection. The repeater would abruptly switch from one rx to the other, which could have a completely different signal on it. Talk about confusion! Even using signal quieting you would have same problem--which is the signal you want to have repeated? What I did was to simply parallel (combine) the audio of two identical FM receivers. (You want ident. rx's so that the audio signs combine precisely.) It cut down on multipath-caused crud noise & distortion considerably. The circuit was super simple (think "KISS"): parallel the speaker outputs; but, these were tube-type radios, the famous Motorola Sensicon (18 tubes, big Permakay filter at one end of chassis) with output xfrms, so paralleling caused no probs. This works because while the actual signal audio is in phase from all the rx's, the non-signal stuff (crud, distortion, etc.) is _not_ in phase. In fact the signals from each rx are coherent with each other & junqe noise is not. When you combine, the signal increases 6 dB but the noise, being uncorrelated increases by less. So, signal SNR increases faster than noise. Leonard Kahn (of "Symmetra Peak" broadcast audio processor fame) found an even better way: combine signals in a ratio equal to the ratio of their signal to noise ratio (e.g. quieting). I haven't done that (yet). The simple combining works well enuf for me. I'd like to try adapting a VHF/UHF wireless mic with a diversity receiver. I'd substitute 10m or 6m front ends & let the voter do its thing. I'd try to get a broken one from a dealer to keep it cheap. BTW, nothing sez that 2m couldn't use diversity reception on repeaters. Groundwave sigs suffer from multipath as well. On HF its tough to get enuf antenna separation to give space diversity gain (a wavelength or two) but easy above HF. --John WB0EQ ======================================================== ________________________________________________________________________ 4b. Re: Squelch action on 10 m FM Posted by: "Paul Plack" [email protected] pw_plack Date: Thu Aug 20, 2009 11:18 pm ((PDT)) John, how's this for an experiment... Configure a repeater with two receivers, one built for +/- 5 kHz deviation, the other for +/- 15, feed them from a splitter, use audio from the narrow one, but allow a DTMF command to select the wider receiver's COS when conditions warrant. (Obviously, those conditions would have to include no adjacent channel signal...) Or, four receivers...I've always wanted to play with H/V polarization diversity when the band was up! ;^) 73, Paul, AE4KR
