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
Re: [Repeater-Builder] Diversity FM reception
Feeding 2 separate V H antennas in phase yields 45 degree polarization. If one antenna is fed 90 degrees lead or lag, then you have RH or LH CP. --Don-- W8DPK larynl2 wrote: ... Years ago before CP antennas were commonly available, FM stations would feed two separate antennas on the tower. One was H, the other V. Was that then 45 degree polarization?? ... Laryn K8TVZ
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: Re: [Repeater-Builder] Diversity FM reception
--- On Mon, 8/24/09, Jeff DePolo j...@broadsci.com wrote: From: Jeff DePolo j...@broadsci.com Subject: RE: Re: [Repeater-Builder] Diversity FM reception To: Repeater-Builder@yahoogroups.com Date: Monday, August 24, 2009, 9:32 PM 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. I refer to another post I just sent, and I tie in another concept. If the reflecting surface is large enough, it's going to reflect both V and H ?components. At VHF and UHF frequencies, any building of appreciable ize s going to reflect both. A typical urban environment comprised of dozens/hundreds of large buildings is going to bounce around enough Vpol and Hpol energy to cause multipath no matter what the originating station was transmitting, H, V, or C. Any surface that is anything other than a perfectly flat plane is going to cause distortion of the incoming wave, distorting/skewing the polarization.. And when it comes to Cpol, the polarization sense is flipped when it is reflected, RHCP becomes LHCP and vice-versa. So, suffice it to say, when you're talking about reflections in an urban environment, or a mountainous region, or in reality, just about anywhere other than in the flatlands with no nearby obstructions (farmhouse with a nice yagi on the roof), you may as well assume you've got mulitpath comprised of a mix of polarizations. Well, just turn your 2m handie talkie even with a rubber ducky on its side note the drop in signal strength. Cross polarization losses, e.g. linear V to linear H (or vice versa) can be up to 30 dB!My data comes from 35 years of reported research in N.A. and Europe. I'm simply reporting what their research found. The BBC and the Deutche Bundespost are very picky about broadcast quality, much more so than the FCC (I speak from personal observation having lived in EU for years). Additional data is from IEEE journals on the subject. Amateur experience is from 'The Practical Handbook of Amateur Radio FM and Repeaters' by Bill Pasternak, WA6ITF, and Mike Morris, WA6ILQ, published by Tab Books. (There may be other amateur sources as well; if anyone knows, pse let me know.) Neither the BBC or the Germans use CP in FM broadcast, strictly H. And they also don't have the FCC, but we won't get into that TV tried abandoned CP due to ghosting. Well, I wouldn't say that. One of the local high-power UHF stations, relatively high in the band, replaced their antenna about 10 years ago, and went to CP. Their coverage noticibly improved. I live about 15 miles from the transmitter and saw quite an improvement. One of our contracts is with one of the new nationwide 700 MHz services that broadcasts digital mobile TV subscription services. Subscribers receive on cell phones with extendable whip antennas. Those can be oriented in any position, but would typically be held vertically. Guess what polarization they're using? Tell we'll both know! My comments only apply to analog TV. UHF experience with CP may be different than VHF. --John
RE: RE: Re: [Repeater-Builder] Diversity FM reception
Well, just turn your 2m handie talkie even with a rubber ducky on its side note the drop in signal strength. Cross polarization losses, e.g. linear V to linear H (or vice versa) can be up to 30 dB! In the absence of multipath, or more correctly, obstructions causing reflections that cause polarization distortion/scattering, yes, you will see typically 20 dB or more of cross-polarization loss if you were to use a Hpol receive antenna to receive a Vpol transmission. That's why FM broadcasters use CP - so that both home listeners using a horizontal wire dipole connected to their stereo, or a roof-mounted yagi or turnstile, can receive Hpol, and mobile listeners with a fender-mounted vertical whip can receive Vpol. If they were to choose one over the other, the other half of their audience would take a 20 dB hit (multipath issues notwithstanding). In many congested areas of the US, such as here in the northeast, your coverage is interference limited. So, even if that 20 dB reduction in one polarization might have still yielded an acceptable signal level under quiet conditions in the absence of co-channel or adajacent-channel interference, we don't have that luxury in the real world here. The listener will suffer that 20 dB increase in U/D (undesired-to-desired signal) ratio. So, here in the ever-competitive US, there's rarely a case to be made for NOT running CP. Translators are also used much more effectively in Europe, as is RDS/RDBS. They're used in combination to fill in holes and to yield a multi-frequency network, frequency-hopping your car radio automatically as you drive around the countryside. Almost a cellular approach. In the US, we go for big signals and maximum range. Just a different philosophy. Quantity counts here. The BBC and the Deutche Bundespost are very picky about broadcast quality, much more so than the FCC (I speak from personal observation having lived in EU for years). Yes, I know. We can talk about ITU-R 412, Eureka, iBiquity, and lots of other things separate us from them, but the topic started with how/why CP was different/better than linear, how/why it was used on FM in the US, and how/why some FM stations uses more or less H versus V. Viva America! God save the queen! --- Jeff WN3A
Re: [Repeater-Builder] Diversity FM reception
--- In Repeater-Builder@yahoogroups.com, Gary Schafer gascha...@... wrote: You can not transmit both horizontal and vertical polarization at the same time. Feeding a horizontal antenna and a vertical in phase will give 45 degree polarization. For simultaneous vertical and horizontal the antennas must be fed as circular. Years ago before CP antennas were commonly available, FM stations would feed two separate antennas on the tower. One was H, the other V. Was that then 45 degree polarization?? TV has no need to transmit anything other than horizontal polarization as most TV reception is done with a horizontal antenna. The local channel 8 analog station here had a CP antenna. To get their 316KW horizontal ERP they put 77KW up the coax from a many-yards-long Larcan transmitter. They had a whopper signal around here and it was very easy to get a great picture even with rabbit ears. I know that their excellent signal wasn't just because of CP, but it had to help. I wonder what their reasons were to go CP? Laryn K8TVZ
Re: [Repeater-Builder] Diversity FM reception
Lots of consumer TV receivers use vertical, telescopic whips. - Original Message - From: larynl2 To: Repeater-Builder@yahoogroups.com Sent: Monday, August 24, 2009 4:23 PM Subject: Re: [Repeater-Builder] Diversity FM reception The local channel 8 analog station here had a CP antenna. To get their 316KW horizontal ERP they put 77KW up the coax from a many-yards-long Larcan transmitter. They had a whopper signal around here and it was very easy to get a great picture even with rabbit ears. I know that their excellent signal wasn't just because of CP, but it had to help. I wonder what their reasons were to go CP? Laryn K8TVZ . ,_._,___
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
RE: 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. I refer to another post I just sent, and I tie in another concept. If the reflecting surface is large enough, it's going to reflect both V and H components. At VHF and UHF frequencies, any building of appreciable size is going to reflect both. A typical urban environment comprised of dozens/hundreds of large buildings is going to bounce around enough Vpol and Hpol energy to cause multipath no matter what the originating station was transmitting, H, V, or C. Any surface that is anything other than a perfectly flat plane is going to cause distortion of the incoming wave, distorting/skewing the polarization. And when it comes to Cpol, the polarization sense is flipped when it is reflected, RHCP becomes LHCP and vice-versa. So, suffice it to say, when you're talking about reflections in an urban environment, or a mountainous region, or in reality, just about anywhere other than in the flatlands with no nearby obstructions (farmhouse with a nice yagi on the roof), you may as well assume you've got mulitpath comprised of a mix of polarizations. Neither the BBC or the Germans use CP in FM broadcast, strictly H. And they also don't have the FCC, but we won't get into that... TV tried abandoned CP due to ghosting. Well, I wouldn't say that. One of the local high-power UHF stations, relatively high in the band, replaced their antenna about 10 years ago, and went to CP. Their coverage noticibly improved. I live about 15 miles from the transmitter and saw quite an improvement. The antenna is a typical slot with sort of Z-shaped parasitic elements on the outside of the slots which couple a little horizontal energy, converting it to vertical, to create the Cpol. One of our contracts is with one of the new nationwide 700 MHz services that broadcasts digital mobile TV subscription services. Subscribers receive on cell phones with extendable whip antennas. Those can be oriented in any position, but would typically be held vertically. Guess what polarization they're using? Also keep in mind that 8VSB isn't the same game as NTSC/VSB, especially when it comes to receivers and how they deal with multipath. What worked well (or didn't work well) for analog TV doesn't hold true for DTV. For example, lowband is no longer the place to be! --- Jeff WN3A
RE: 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. If you're going to use CP on a repeater, I don't see why you would want to also mix in linear H and/or V, nor why you would want both LHCP and RHCP. The users are all going to be using linear polarization. As long as you are using one rotation of CP, that's all you need. 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. Most FM uses CP - true. Why some FM stations use only V or only H or some ellipitical ratio where H V is for a variety of reasons, but here are the most common: 1. Historically, FM, like TV, was predominantly horizontally polarized. The regulations, to this day, still favor the use of horizontal polarization, and with few exceptions (especially #2 below), you have to have at least as much horizontal power as vertical power. Commercial stations in the non-reserved band (i.e. above 92 MHz) that are still running horizontal-only are doing so by choice, not by rule. It wasn't until car radios with vertical whip antennas started to gain popularity did vertical polarization start to become important, and CP resulted as a solution to satisfy listeners using either horizontal or vertical antennas, while improving multipath performance as a side-benefit. Of course this also meant that broadcasters needed 2X the transmitter power, or 2X the number of antenna bays, to achieve the same amount of ERP, to convert from H to CP. 2. Non-commercial stations in the reserved band (i.e. below 92 MHz) that are within the affected area of a channel 6 TV station are required to protect that channel 6 station. The rules regarding how this protection is accomplished are the most twisted, tangled mess of lawerese engineering that ever came out of the FCC IMHO. Anyway, in order to afford protection to channel 6 TV, which is horizontal, non-comm FM's often end up being restricted to less H than V (or sometimes V only) in order to get the population within the interference area down to allowable levels. The Channel 6 rules of 47 CFR 73.525 are the cause for probably the majority of cases where FM stations have more V than H. 3. Directional antennas. In cases where stations are using a directional antenna to meet protection requirements, the measured pattern of the directional antenna may have been such that the peak horizontal power may have been different than the peak vertical power, and, as such, the licensed H and V ERP values reflect that difference. The station where I'm typing from currently has a directional antenna that was designed supposedly such that H = V, but when they put it on the antenna range, the measured pattern came out with H V in the major lobe, resulting in it being licensed for 12.5 kW horizontal and 11 kW vertical. --- Jeff WN3A
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
RE: Re: [Repeater-Builder] Diversity FM reception
The reason FM stations transmit circular polarization is to accommodate both horizontal and vertical receive antennas. Most fixed receivers are horizontal and most cars are vertical. You can not transmit both horizontal and vertical polarization at the same time. Feeding a horizontal antenna and a vertical in phase will give 45 degree polarization. For simultaneous vertical and horizontal the antennas must be fed as circular. They then contain both the horizontal and vertical component. They are not doing this for the sake of circular polarization but only so vertical and horizontal polarizations can be transmitted together. TV has no need to transmit anything other than horizontal polarization as most TV reception is done with a horizontal antenna. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of John Sehring Sent: Sunday, August 23, 2009 12:51 AM To: Repeater-Builder@yahoogroups.com Subject: 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
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.
Re: [Repeater-Builder] Diversity FM reception
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 - Original Message - From: John Sehring To: Repeater-Builder@yahoogroups.com Sent: Friday, August 21, 2009 11:11 AM Subject: [Repeater-Builder] Diversity FM reception 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... .
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.
