Re: Fw: Re: [Repeater-Builder] Diversity FM reception
On Fri, 21 Aug 2009, John Sehring wrote: Then of course 12 identical receivers, I'd use, oh, Mitrek's or MaxTrac's. I think I'd not be inclined to use Micor or any of the Syntor radios because they are purpose-designed radios for quite wide freq. spreads. This necessarily makes for the compromise of a wider RF mixer front end. I think I'd like maximum RF selectivity on both 10m and 6m (the latter esp. where TV ch. 2 is used on the air. The Syntor (not Syntor X or Syntor X9000) has the selectivity of a Mitrek, with a synthesized and programmable receiver. The spread on the front end of the Mitrek, Micor, and Syntor is 2MHz. The Syntor X, X9000, Spectra, Maxtrac, etc. is 22-24MHz. And at this point, if you show interest in Mitreks, you can probably receive a lifetime supply for shipping. Next would come the rx voting scheme. It'd have to be carefully designed (the squelch ct's, too, probably no Micor-style circuit here). Maybe a combination of quieting and signal strength would be used for rx selection or combining (see my earlier note). Motorola once (abt. 1960) had a squelch ct. which fed a bit of audio into the noise amp to inhibit squelch clamping on modulation. It also used a bit of both 1st 2nd limiter levels in the mix. I don't know that it ever was commercialized. Digital backhaul means that you don't have to equalize the radio link. And you're going to have four receivers from each site, so you'll want to find some way to multiplex them. -- Kris Kirby, KE4AHR Disinformation Analyst
Fw: Re: [Repeater-Builder] Diversity FM reception
Well, I have only one observation on this statment. In late 70's or early 80's CP was the proposed solution to ghosting. WTTV - 4 Bloomington converted to CP for that exact reason. Working in the field we documented the difference at a receive site. I still have the Poloraid's somewhere but it was a significant improvement I can say. Of course getting the recieve ant's for CP was not an option, which would have given an additional improvement, per the Ch4 chief engineer. That was for a single data point I grant you, and maybe as many seen a downgraded picture, but I can't say for sure on that. Sure seems curious to me. Randy --- In Repeater-Builder@yahoogroups.com, John Sehring wb...@... wrote: TV tried abandoned CP due to ghosting. With color TV, the ghosting is even more obnoxious. This I have on the authority of the VP of Engineering of one of the largest national Canadian TV networks (he's a ham).
Fw: Re: [Repeater-Builder] Diversity FM reception
Yes, CP does cause more multipath esp. in urban environments. Turns out there are a large number of buildings the preferentially reflect V better than H. CP gives V energy othwise lacking (mostly) in a strictly H xmt situation. What you get with strictly H pol. is quite a glorious random mess of polarizations. Neither the BBC or the Germans use CP in FM broadcast, strictly H. Yes, 2X antenna gain or 2X power are needed to equalize things. TV tried abandoned CP due to ghosting. With color TV, the ghosting is even more obnoxious. This I have on the authority of the VP of Engineering of one of the largest national Canadian TV networks (he's a ham). - From: larynl2 lar...@hotmail.com Subject: Fw: Re: [Repeater-Builder] Diversity FM reception To: Repeater-Builder@yahoogroups.com Date: Sunday, August 23, 2009, 11:52 AM --- In Repeater-Builder@ yahoogroups. com, John Sehring wb...@... wrote: Oh, I forgot...circular polarization would be excellent to use on VHF and UHF repeater. We want the extra signal strength the multipath would be way less; CP has always intrigued my for amateur repeater use, although I've not tried it yet. Yes there would be less multipath fading, but the extra signal strength woulnd't appear unless you keep the same ERP in both H and V. And that requires a larger antenna or double the transmitter power. John is it really true that CP causes MORE multipath distortion in FM broadcast?? And TV?? Laryn K8TVZ
Fw: Re: [Repeater-Builder] Diversity FM reception
--- In Repeater-Builder@yahoogroups.com, John Sehring wb...@... wrote: Oh, I forgot...circular polarization would be excellent to use on VHF and UHF repeater. We want the extra signal strength the multipath would be way less; CP has always intrigued my for amateur repeater use, although I've not tried it yet. Yes there would be less multipath fading, but the extra signal strength woulnd't appear unless you keep the same ERP in both H and V. And that requires a larger antenna or double the transmitter power. John is it really true that CP causes MORE multipath distortion in FM broadcast?? And TV?? Laryn K8TVZ
Fw: Re: [Repeater-Builder] Diversity FM reception
I turn out that use of CP in urban suburban areas results in somewhat more signal strength on linearly polarized antennas, e.g. vertical whips on cars straight rod aerials on portable FM radios. Due to preferential scattering of vertically polarized sigs from typical urban structures, there tends to be more of that available, esp. good for auto FM reception. The Germans for example are more concerned with signal quality than quantity so don't use CP. However, there is a drawback: there's more multipath. So the tradeoff was made--more signal strength but at lesser quality (due to multipath distortion). Well designed FM radios reduce separation intelligently in the presence of multipath: first they gradually blend the stereo channels into mono, high audio frequencies L-R info first, then all audio (L+R) is gradually lowpass filtered. This happens dynamically, on the fly. Works well IMO when done properly. TV broadcasters tried CP as well but couldn't live the extra multipath: it was easily visible as more ghosting. See for example: http://www.ham-radio.com/k6sti/ for more on this. --John --- On Fri, 8/21/09, larynl2 lar...@hotmail.com wrote: From: larynl2 lar...@hotmail.com Subject: Fw: Re: [Repeater-Builder] Diversity FM reception To: Repeater-Builder@yahoogroups.com Date: Friday, August 21, 2009, 9:08 PM In reference to below, what would be the real advantage to using CP antennas in addition to the V and H you'd have already? Any signal that arrives will excite a V and/or H antenna according to it's arriving polarization, and I don't see where CP would be a help. Most FM broadcasters use CP. Those that don't are licensed for only V or H or choose to use a less-expensive single-polarization antenna. And many of them look like rototillers, and other shapes. Laryn K8TVZ --- In Repeater-Builder@ yahoogroups. com, John Sehring wb...@... wrote: There's more to be done with polarization as well: Circular, both RH LH. It is possibile to make omnidirectional CP antennas. FM broadcasters use a lot of them. They look like a bunch of arrows.
Fw: Re: [Repeater-Builder] Diversity FM reception
Oh, I forgot...circular polarization would be excellent to use on VHF and UHF repeater. We want the extra signal strength the multipath would be way less; less deviation 5 kHz vs. 75 kHz means less susceptability to multipath. Pasternak's Repeater Handbook shows actual results. --- On Fri, 8/21/09, larynl2 lar...@hotmail.com wrote: From: larynl2 lar...@hotmail.com Subject: Fw: Re: [Repeater-Builder] Diversity FM reception To: Repeater-Builder@yahoogroups.com Date: Friday, August 21, 2009, 9:08 PM In reference to below, what would be the real advantage to using CP antennas in addition to the V and H you'd have already? Any signal that arrives will excite a V and/or H antenna according to it's arriving polarization, and I don't see where CP would be a help. Most FM broadcasters use CP. Those that don't are licensed for only V or H or choose to use a less-expensive single-polarization antenna. And many of them look like rototillers, and other shapes. Laryn K8TVZ --- In Repeater-Builder@ yahoogroups. com, John Sehring wb...@... wrote: There's more to be done with polarization as well: Circular, both RH LH. It is possibile to make omnidirectional CP antennas. FM broadcasters use a lot of them. They look like a bunch of arrows.
Fw: Re: [Repeater-Builder] Diversity FM reception
Right you are, Paul. However, all it takes is several wavelength's of physical separation to reap all of the diversity gain. Of course, that's not gain in the usual sense. Antenna diversity has been known of since the 1920s. To get even more diversity, one could have two sets of H V polarized antennas separated by several lambda's, driving 4 receivers. There's more to be done with polarization as well: Circular, both RH LH. It is possibile to make omnidirectional CP antennas. FM broadcasters use a lot of them. They look like a bunch of arrows. Ok, here's my dream (large land, large wallet): Three sites spaced several lambda's apart. Each would have H omni, V omni, CPRH and CPLH. I'd want each antenna to have some omni gain. For H, I'd stack two or more of crossed dipoles (turnstile, they each have a gain zero dBd or less); for V, I'd stack two or four VHF-style folded dipoles 360 degrees around a mast; for the CP's, I'd use the FM broadcaster-style omni CP's stacked. I've always wanted a 10m antenna that would give me V, H, CPRH CPLH at the flick of a switch. A pair of crossed Yagi's would give that 2 flavors of linear slant polarization, too, 135 45 degrees. I'd cross 'em at 45 135 degrees to somewhat avoid metal mast coupling effects. Wish I had a really strong piece of fibreglas mast, say 1.25x10' to avoid that. I think that a vert. pol. Yagi on a metal mast will throw its performance way off. The only proper way to do that is ti end-mount the yagi about 0.2 wavelengths from the mast. I see it a lot on VHF UHF in point to point service. It's also possible to feed both sides of the same square Quad at the same time, with 2 sep. feedlines. You'd then combine them as with crossed Yagis. I knew a guy who had crossed Yagi's on 10 m. He told me that with F2 signals, the maximum signal would drift among the various polarizations, i.e. no one was always best. Then of course 12 identical receivers, I'd use, oh, Mitrek's or MaxTrac's. I think I'd not be inclined to use Micor or any of the Syntor radios because they are purpose-designed radios for quite wide freq. spreads. This necessarily makes for the compromise of a wider RF mixer front end. I think I'd like maximum RF selectivity on both 10m and 6m (the latter esp. where TV ch. 2 is used on the air. Next would come the rx voting scheme. It'd have to be carefully designed (the squelch ct's, too, probably no Micor-style circuit here). Maybe a combination of quieting and signal strength would be used for rx selection or combining (see my earlier note). Motorola once (abt. 1960) had a squelch ct. which fed a bit of audio into the noise amp to inhibit squelch clamping on modulation. It also used a bit of both 1st 2nd limiter levels in the mix. I don't know that it ever was commercialized. I can dream, can't I? --John WB0EQ/VE6 --- On Fri, 8/21/09, Paul Plack pl...@xmission.com wrote: From: Paul Plack pl...@xmission.com Subject: Re: [Repeater-Builder] Diversity FM reception To: Repeater-Builder@yahoogroups.com Date: Friday, August 21, 2009, 1:34 PM When I lived in Atlanta in the 80's I was a few miles from the local 10m repeater, and quickly noticed that distant stations which were fading on the repeater input had climbing signal strength at my location if I switched to the input. About the time they started getting ratty at my place, I could switch back to the repeater output, and they were solid there. I think, on 10m, voting receivers separated by a few miles could actually be of greater help for maintaining communications with distant stations than for local mobiles. 73, Paul, AE4KR ,_._,___
Fw: Re: [Repeater-Builder] Diversity FM reception
In reference to below, what would be the real advantage to using CP antennas in addition to the V and H you'd have already? Any signal that arrives will excite a V and/or H antenna according to it's arriving polarization, and I don't see where CP would be a help. Most FM broadcasters use CP. Those that don't are licensed for only V or H or choose to use a less-expensive single-polarization antenna. And many of them look like rototillers, and other shapes. Laryn K8TVZ --- In Repeater-Builder@yahoogroups.com, John Sehring wb...@... wrote: There's more to be done with polarization as well: Circular, both RH LH. It is possibile to make omnidirectional CP antennas. FM broadcasters use a lot of them. They look like a bunch of arrows.
