[Repeater-Builder] Antenna Separation UHF Low Power
I am looking at putting together a 5w uhf repeater using 2 uhf m200s and a Rick we have on hand. We want to do coverage tests prior to investing in a duplexer, how far apart do we need to place our antennas?
RE: [Repeater-Builder] Antenna Separation UHF Low Power
There's should be more in your question. Are they going to be tower mounted where they will be directly above and below the other. That's very important. If so I'd say at least 70'-100' of vertical separation but if your not running hardline with no filtering whatsoever you will still likely have problems with desense just through the coax feedlines. If the separation isn't exactly vertical say on two towers on a site. Even with one antenna at 50' and the other is at 200' the towers would need to be hundreds, maybe thousands of feet separation. A pair of simple pass cans could give you what you need for isolation. No UHF Moto cube cans lying around??? Also you can try more of a split just for testing. 435rx 449tx say. Ross kc7rjk -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Steve Sent: Wednesday, June 02, 2010 2:30 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna Separation UHF Low Power I am looking at putting together a 5w uhf repeater using 2 uhf m200s and a Rick we have on hand. We want to do coverage tests prior to investing in a duplexer, how far apart do we need to place our antennas?
Re: [Repeater-Builder] Antenna Separation UHF Low Power
Do your coverage tests with one radio at the repeater site and use simplex. Someone stays with the radio for the testing. Chuck WB2EDV - Original Message - From: Steve mill1...@gmail.com To: Repeater-Builder@yahoogroups.com Sent: Wednesday, June 02, 2010 5:30 PM Subject: [Repeater-Builder] Antenna Separation UHF Low Power I am looking at putting together a 5w uhf repeater using 2 uhf m200s and a Rick we have on hand. We want to do coverage tests prior to investing in a duplexer, how far apart do we need to place our antennas? Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.829 / Virus Database: 271.1.1/2913 - Release Date: 06/02/10 05:57:00
Re: [Repeater-Builder] Antenna Separation UHF Low Power
Suitable 6 cavity Flat Pack mobile duplexers are in the $100 range on eBay. Thats probably cheaper than the feedline and second antenna. On Wed, Jun 2, 2010 at 5:10 PM, Chuck Kelsey wb2...@roadrunner.com wrote: Do your coverage tests with one radio at the repeater site and use simplex. Someone stays with the radio for the testing. Chuck WB2EDV - Original Message - From: Steve mill1...@gmail.com To: Repeater-Builder@yahoogroups.com Sent: Wednesday, June 02, 2010 5:30 PM Subject: [Repeater-Builder] Antenna Separation UHF Low Power I am looking at putting together a 5w uhf repeater using 2 uhf m200s and a Rick we have on hand. We want to do coverage tests prior to investing in a duplexer, how far apart do we need to place our antennas? Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.829 / Virus Database: 271.1.1/2913 - Release Date: 06/02/10 05:57:00 Yahoo! Groups Links
[Repeater-Builder] Antenna separation question
Ok just kicking this idea around the other day and the question came up about antenna separation. I know the basic 2 meter antenna separation is 50ft. (I am thinking 60ft to be safe) But is it possible to get them closer if I place some cavities on either the receive or transmit sides. Sounds dumb from some certian points of view, but I am waiting on the arrival of a decent duplexer (could be some time out though)so in the mean time I would like to get this up and going with a split antenna system for now. I was thinking maybe a 30ft separation... Would this idea work? If so does it need to be modified from what I was thinking?
Re: [Repeater-Builder] Antenna separation question
Certainly it will work as it is done all the time. Isolation is isolation - if you have enough, it doesn't matter how you got it. Chuck WB2EDV - Original Message - From: kc0mlt kc0...@yahoo.com To: Repeater-Builder@yahoogroups.com Sent: Tuesday, June 01, 2010 1:27 PM Subject: [Repeater-Builder] Antenna separation question Ok just kicking this idea around the other day and the question came up about antenna separation. I know the basic 2 meter antenna separation is 50ft. (I am thinking 60ft to be safe) But is it possible to get them closer if I place some cavities on either the receive or transmit sides. Sounds dumb from some certian points of view, but I am waiting on the arrival of a decent duplexer (could be some time out though)so in the mean time I would like to get this up and going with a split antenna system for now. I was thinking maybe a 30ft separation... Would this idea work? If so does it need to be modified from what I was thinking? Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.819 / Virus Database: 271.1.1/2910 - Release Date: 06/01/10 02:25:00
RE: [Repeater-Builder] Antenna separation question
That's exactly what I'm doing. VHF GE mastrII at 100 watts goes through 2 8 Sinclair pass cavities set at .5db gives 80 watts to the antenna. 4 bay exposed dipole at 75' The receiver and preamp goes through only one 8 Wacom also set at .5db then up to the collinear receive antenna at 100' Very very little desense almost undetectable. Also with the pass cavity on the receiver side preamps seem to be much more usable and effective in the real world. This machine hears very very well! More can be seen from my website. www.kc7rjk.net http://www.kc7rjk.net/ ~Ross -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kc0mlt Sent: Tuesday, June 01, 2010 10:28 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna separation question Ok just kicking this idea around the other day and the question came up about antenna separation. I know the basic 2 meter antenna separation is 50ft. (I am thinking 60ft to be safe) But is it possible to get them closer if I place some cavities on either the receive or transmit sides. Sounds dumb from some certian points of view, but I am waiting on the arrival of a decent duplexer (could be some time out though)so in the mean time I would like to get this up and going with a split antenna system for now. I was thinking maybe a 30ft separation... Would this idea work? If so does it need to be modified from what I was thinking?
[Repeater-Builder] Antenna separation for UHF repeater operation
Hello: I realize this question must be old boring stuff nonetheless I will ask it. I'm planning on installing a GMRS repeater and I would like to use two antennas instead of a Duplexer/Antenna combination. What would be a good separation distance for a standard Split of 5 MHZ, two 5 dB antennas an 35 Watts of power?. Thanks in advance...
RE: [Repeater-Builder] Antenna separation for UHF repeater operation
If we assume that both antennas are identical and mounted inline and directly one above the other, and assuming a receiver sensitivity of 0.25 uV, a vertical spacing of 39 feet should provide sufficient isolation between RX and TX. This assumes solid-shield RX feedline, such as Heliax, with the RX antenna at the top. Obviously, more separation is better. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Aisen Lopez Sent: Sunday, May 31, 2009 6:16 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna separation for UHF repeater operation Hello: I realize this question must be old boring stuff nonetheless I will ask it. I'm planning on installing a GMRS repeater and I would like to use two antennas instead of a Duplexer/Antenna combination. What would be a good separation distance for a standard Split of 5 MHz, two 5 dB antennas and 35 Watts of power?. Thanks in advance..
Re: [Repeater-Builder] Antenna separation for UHF repeater operation
20ft. Vertical separation assuming vertically polarized omni antennas are used. Alan Sent from my Verizon Wireless BlackBerry -Original Message- From: Aisen Lopez aisendwi...@yahoo.com Date: Sun, 31 May 2009 18:16:14 To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna separation for UHF repeater operation Hello: I realize this question must be old boring stuff nonetheless I will ask it. I'm planning on installing a GMRS repeater and I would like to use two antennas instead of a Duplexer/Antenna combination. What would be a good separation distance for a standard Split of 5 MHZ, two 5 dB antennas an 35 Watts of power?. Thanks in advance...
Re: [Repeater-Builder] Antenna separation article
Gary Schafer wrote: * I notice in the below referenced article on antenna separation that it is stated that the graphs are misleading and no where near accurate for modern day solid state equipment.* http://www.repeater-builder.com/antenna/separation.html http://www.repeater-builder.com/antenna/separation.html * * *That is not correct as the graphs for antenna isolation show approximately how much isolation can be expected with a given amount of separation either vertically or horizontally. This has nothing to do with the amount of isolation NEEDED for proper duplex operation.* Agreed, The graphs in no way indicate what is needed, they show, approximately, what isolation is provided. While it is stated that I am a contributing author for this page, I am not. This page was originally only the scanned graphs and links were provided to them. Mike Morris did the text, as verified in this archived article: http://web.archive.org/web/20040617072700/http://www.repeater-builder.com/antenna/separation.html I'm not sure how the credit line got changed, but Mike will correct it for technical accuracy, and also correct the credit lines to match reality. Kevin Custer
RE: [Repeater-Builder] Antenna separation article
I notice in the below referenced article on antenna separation that it is stated that the graphs are misleading and no where near accurate for modern day solid state equipment. That is not correct as the graphs for antenna isolation show approximately how much isolation can be expected with a given amount of separation either vertically or horizontally. This has nothing to do with the amount of isolation NEEDED for proper duplex operation. I think the author(s) who wrote text in that article were thinking of the duplex isolation curves (such as the ones published by GE), not the antenna separation curves that followed in the article. Those curves are published elsewhere on the site; maybe a link to them should be in the text. Regardless, measurement of isolation is a lot more accurate and reliable than using graphs. For two co-located antennas, it's easy to from one to the other to measure the actual isolation. For distant antennas, path models and/or free-space calculations are easy enough to do from behind the desk, or do RSL measurements while transmitting using a calibrated test signal from the opposite site. As another note in the article it suggested using a spectrum analyzer to tune the receiver's local oscillator chain for lowest noise. While that is one approach, an easier and probably more accurate way of doing it is to use a sinadder on the receiver while tuning it up. Tuning everything for best sinadd will result in best signal to noise performance of the receiver which would also include lowest noise out of the local oscillator chain. While you might be able to eek out a fraction of a dB more sensitivity by peaking the LO for maximum SINAD (which would likely be the point at maximum LO injection), without looking at it spectrally, how can you tell whether or not the LO is spurious? A spurious LO, especially one that comes and goes, is a miserable situation. You're better off tuning the LO multiplier stages by following the factory procedure, especially if you don't have a spectrum analyzer available. I hope I don't step on any toes here. Those of us that have been on here a while wear steel-toed boots. They're good for both defense as well as offense :-) --- Jeff
RE: [Repeater-Builder] Antenna separation article
Hi Mike, That is a nice article. Someone else suggested that the reference to old curves should have been to the older tx-rx isolation curves that were published by GE. Those are also valuable as a starting point in figuring total isolation needed. I agree that those are very tx-rx type dependent. You might want to incorporate those into the article or that part might best be left to another article (maybe one already exists?). It could be noted that those curves represent an approximate amount of isolation needed but with a caveat that all tx and rx are not created equal. The graphs of antenna separation are typical of isolation provided by antenna separation distance. If additional isolation is needed it would be necessary to add cavities to the transmitter and or receiver in order to obtain the total isolation needed as indicated by the tx-rx isolation curves with a note that those curves may or may not be adequate depending on transmitter and receiver quality. If sticking to antenna separation, then I would reword that part to deal only with isolation available with antenna separation. As another note on the tx-rx isolation curves, a synthesized transmitter is not always worse than a crystal controlled transmitter as far as broad band noise output. If I remember right There are somewhere some curves showing that a certain model GE synthesized transmitter has less broad band noise than a typical crystal controlled transmitter therefore requiring less isolation in a duplex operation. Isolation curves used to be available for many tx-rx combinations. Very handy when selecting a duplexer for a particular setup. This leads to another subject, duplexer isolation. Lots of people are under the impression that if a duplexer that is adequate with 70 db of isolation and provides no desense then using one with 100 db of isolation will be much better. In this case the 100 db duplexer is only better at emptying your wallet. Once you have reached the needed isolation, more does nothing for you. RECEIVER FRONT ENDS Some of the older radios obtained their intermod specs by using very narrow front end filters. Some of the newer radios have much wider front ends and provide the same intermod performance. This is because the newer radios have much better dynamic range in the mixer. It is all about how much total power a mixer can handle before being overloaded. The narrower the front end filter the less total signal power reaches the mixer. All signals received add together in the mixer and are a determining factor in overload not just the strongest signals. SPECTRUM ANALYZER Good point about using the spectrum analyzer to look for/ tune for minimum spurs in the local oscillator. One thing to watch out for when using a spectrum analyzer and watching for low level noise or spurs along with a large signal (either on a receiver or a transmitter) is overload on the analyzer. I have seen many people fooled by analyzer overload and false apparent spurs etc. created within the analyzer itself. This is particularly true of analyzers that are incorporated within a service monitor. Most suffer badly from lack of dynamic range. Using a sharp notch tuned to the strong signal will often allow you to look much further down to reliably see other noise and spurs. This got longer than expected. 73 Gary K4FMX -Original Message- From: Mike Morris WA6ILQ [mailto:[EMAIL PROTECTED] I notice in the below referenced article on antenna separation that it is stated that the graphs are misleading and no where near accurate for modern day solid state equipment. http://www.repeater-builder.com/antenna/separation.html That is not correct as the graphs for antenna isolation show approximately how much isolation can be expected with a given amount of separation either vertically or horizontally. This has nothing to do with the amount of isolation NEEDED for proper duplex operation. Very true. I should have pointed that out. The amount of isolation needed is a function of the transmitter and receiver being used. One type of tx-rx combination may need a different amount of isolation than another type used with the same antenna isolation. Maybe someone would want to correct the above? I wrote that article, and you have pointed out something that needs to be changed. THANK YOU. And if you have a better way of saying it, I'd be glad to hear your suggested rewording.
RE: [Repeater-Builder] Antenna separation article
As another note on the tx-rx isolation curves, a synthesized transmitter is not always worse than a crystal controlled transmitter as far as broad band noise output. If I remember right There are somewhere some curves showing that a certain model GE synthesized transmitter has less broad band noise than a typical crystal controlled transmitter therefore requiring less isolation in a duplex operation. I was told that one of the design critieria for GE Delta-S/SX series mobiles was that the transmitter noise was required to be LESS than that of the Mastr II series PLL exciter. Some circuitry in Mastr III series equipment is similiar to that found in the Delta-S, so maybe that's what you're remembering. This leads to another subject, duplexer isolation. Lots of people are under the impression that if a duplexer that is adequate with 70 db of isolation and provides no desense then using one with 100 db of isolation will be much better. In this case the 100 db duplexer is only better at emptying your wallet. Once you have reached the needed isolation, more does nothing for you. Except you have to take into account external influences that may affect Z, phase, noise, etc., including those caused by changes in temperature and humidity. Just squeaking by with 70 dB under perfect conditions doesn't mean that you'll still have no desense when there's ice on the antenna or the building tempature spikes at 120 when the HVAC fails. It is all about how much total power a mixer can handle before being overloaded. The narrower the front end filter the less total signal power reaches the mixer. All signals received add together in the mixer and are a determining factor in overload not just the strongest signals. Well, sure, but if you take 99% of the out-of-band signals out of the mix via tight filtering, you've eliminated the potential for that many mixes from occuring. This is particularly true of analyzers that are incorporated within a service monitor. Most suffer badly from lack of dynamic range. Yes. Even good SM's like 8920's are easily overloaded, often making harmonics appear grossly exaggerated when transmitting into the RF in/out port. If you can reduce the input level by adding X dB of attenuation, and you see the harmonic drop by greater than X dB, you know that you're overloading the instrument... Using a sharp notch tuned to the strong signal will often allow you to look much further down to reliably see other noise and spurs. Not really practical when using the RF in/out port on a service monitor. You'd need to use a lightly-coupled sampler or directional coupler, with the transmitter operating into the antenna or dummy load, otherwise the transmitter would be looking into a very bad (and potentially damaging) load Z. --- Jeff
RE: [Repeater-Builder] Antenna separation article
_ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo This leads to another subject, duplexer isolation. Lots of people are under the impression that if a duplexer that is adequate with 70 db of isolation and provides no desense then using one with 100 db of isolation will be much better. In this case the 100 db duplexer is only better at emptying your wallet. Once you have reached the needed isolation, more does nothing for you. Except you have to take into account external influences that may affect Z, phase, noise, etc., including those caused by changes in temperature and humidity. Just squeaking by with 70 dB under perfect conditions doesn't mean that you'll still have no desense when there's ice on the antenna or the building tempature spikes at 120 when the HVAC fails. Agreed, you need some margin but not a ton. My point was that some believe that extra margin in itself makes for better performance. It is all about how much total power a mixer can handle before being overloaded. The narrower the front end filter the less total signal power reaches the mixer. All signals received add together in the mixer and are a determining factor in overload not just the strongest signals. Well, sure, but if you take 99% of the out-of-band signals out of the mix via tight filtering, you've eliminated the potential for that many mixes from occurring. Agreed, but my main point was that newer receivers even though wide band may be as good as older narrow band receivers. No question that additional filtering makes them even better. This is particularly true of analyzers that are incorporated within a service monitor. Most suffer badly from lack of dynamic range. Yes. Even good SM's like 8920's are easily overloaded, often making harmonics appear grossly exaggerated when transmitting into the RF in/out port. If you can reduce the input level by adding X dB of attenuation, and you see the harmonic drop by greater than X dB, you know that you're overloading the instrument... Using a sharp notch tuned to the strong signal will often allow you to look much further down to reliably see other noise and spurs. Not really practical when using the RF in/out port on a service monitor. You'd need to use a lightly-coupled sampler or directional coupler, with the transmitter operating into the antenna or dummy load, otherwise the transmitter would be looking into a very bad (and potentially damaging) load Z. When looking for spurious products on a transmitter one should never feed the transmitter directly into a service monitor. The transmitter should be feed to a directional coupler and dummy load or a high power attenuator and coupled to the monitor. It is too easy to overload the monitor. Even stray coupling paths within the monitor when using its internal load can cause problems. 73 Gary K4FMX --- Jeff
RE: [Repeater-Builder] Antenna separation article
Agreed, but my main point was that newer receivers even though wide band may be as good as older narrow band receivers. No question that additional filtering makes them even better. Do you have a particular wide-band receiver in mind? --- Jeff
[Repeater-Builder] Antenna separation article
I am rather new to this group and maybe shouldn't be critical of anything on the site at this stage but here it goes anyway. I notice in the below referenced article on antenna separation that it is stated that the graphs are misleading and no where near accurate for modern day solid state equipment. http://www.repeater http://www.repeater-builder.com/antenna/separation.html -builder.com/antenna/separation.html That is not correct as the graphs for antenna isolation show approximately how much isolation can be expected with a given amount of separation either vertically or horizontally. This has nothing to do with the amount of isolation NEEDED for proper duplex operation. The amount of isolation needed is a function of the transmitter and receiver being used. One type of tx-rx combination may need a different amount of isolation than another type used with the same antenna isolation. Maybe someone would want to correct the above? As another note in the article it suggested using a spectrum analyzer to tune the receiver's local oscillator chain for lowest noise. While that is one approach, an easier and probably more accurate way of doing it is to use a sinadder on the receiver while tuning it up. Tuning everything for best sinadd will result in best signal to noise performance of the receiver which would also include lowest noise out of the local oscillator chain. I hope I don't step on any toes here. 73 Gary K4FMX
Re: [Repeater-Builder] Antenna separation article
At 2/5/2007 19:51, you wrote: As another note in the article it suggested using a spectrum analyzer to tune the receiver s local oscillator chain for lowest noise. While that is one approach, an easier and probably more accurate way of doing it is to use a sinadder on the receiver while tuning it up. Tuning everything for best sinadd will result in best signal to noise performance of the receiver which would also include lowest noise out of the local oscillator chain. Yes, but there is another major consideration when talking about repeater receivers ( this is the Repeater-Builder list): dynamic range. Tuning the LO for best SINAD gives you best sensitivity, but if the LO has significant spurious content, that will translate into spurious responses in the receiver. The LO tuning instructions for the G.E. MVP/Exec II/Mastr II RXs do not take SINAD into consideration except for the final step, where you're allowed to make only minor tweaks to the LO tuning. This is probably to assure that the LO stays clean. Bob NO6B
Re: [Repeater-Builder] Antenna Separation
At 1/16/2005 01:06 PM, you wrote: Eric, I stand corrected. It is not a circulator, but a DCI Band Pass Filter. The local radio repair shop I deal with called it a preselector. So it sounds like what I need to due is look for a duplexer for one antenna. The repeater is 15 watts, will do 40, but I wanted it less than 1/2 power. Rod Try a pass cavity on the TX. I ran a two meter repeater (GE MVP) with nothing on the RX 11 diameter Motorola pass can circulator on the TX with only 60 ft. of vertical separation (43 ft. from tip to base). No IMD, no desense. Bob NO6B Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Antenna Separation
Rod, I put some typical numbers into my CommShop for Windows program and came up with some recommendations that may surprise you. Assuming a 25 watt GM300 and 0.35 microvolt sensitivity, the program recommends 84.21 dB of isolation. This can be achieved with two identical antennas, in line with each other and separated vertically by 169 feet. A 40 watt radio calls for 86.25 dB of isolation or a vertical separation of 191 feet. These numbers do not consider all of the factors that might affect the outcome, and are based on zero desense. A separation of less than one-tenth of the recommended separation is guaranteed to result in major desense. I am surprised that it works at all. A bandpass cavity on the receiver certainly is a good idea, and it may explain your relative success, but I don't understand the use of a circulator on the receiver. Please advise the make and model of this circulator, and how you have connected it. 73, Eric Lemmon WB6FLY [EMAIL PROTECTED] wrote: I am sure this has been asked before, but I did a search archive on the subject and came up with 0. I have a GR 300 repeater with no duplexer, so I need 2 antennas. I tried a Larson mobile antenna w/ the ground radials as the receive antenna and the same for the tx antenna. These are mounted on a Station Master type antenna tube (the guts were pulled out because it was untunable for 2 meters). The rx ant at the top and the tx ant at the bottom, about 12' to 14' separation. The system would talk to itself. I removed the tx ant and replaced with a 4 ele yagi - works good. I need a omni ant for both rx and tx. I have an isolator on the tx and a Bp cavity and a circulator on the rx. Why would it desense with one ant and not the other ant? I know the idea behind the yagi and the mobile ant. But they both have rf going vertical. I need to have minimal separation without it talking to itself. Your ideas? Thank you. Rod Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Antenna Separation
Eric, I stand corrected. It is not a circulator, but a DCI Band Pass Filter. The local radio repair shop I deal with called it a preselector. So it sounds like what I need to due is look for a duplexer for one antenna. The repeater is 15 watts, will do 40, but I wanted it less than 1/2 power. Rod Rod, I put some typical numbers into my CommShop for Windows program and came up with some recommendations that may surprise you. Assuming a 25 watt GM300 and 0.35 microvolt sensitivity, the program recommends 84.21 dB of isolation. This can be achieved with two identical antennas, in line with each other and separated vertically by 169 feet. A 40 watt radio calls for 86.25 dB of isolation or a vertical separation of 191 feet. These numbers do not consider all of the factors that might affect the outcome, and are based on zero desense. A separation of less than one-tenth of the recommended separation is guaranteed to result in major desense. I am surprised that it works at all. A bandpass cavity on the receiver certainly is a good idea, and it may explain your relative success, but I don't understand the use of a circulator on the receiver. Please advise the make and model of this circulator, and how you have connected it. 73, Eric Lemmon WB6FLY [EMAIL PROTECTED] wrote: I am sure this has been asked before, but I did a search archive on the subject and came up with 0. I have a GR 300 repeater with no duplexer, so I need 2 antennas. I tried a Larson mobile antenna w/ the ground radials as the receive antenna and the same for the tx antenna. These are mounted on a Station Master type antenna tube (the guts were pulled out because it was untunable for 2 meters). The rx ant at the top and the tx ant at the bottom, about 12' to 14' separation. The system would talk to itself. I removed the tx ant and replaced with a 4 ele yagi - works good. I need a omni ant for both rx and tx. I have an isolator on the tx and a Bp cavity and a circulator on the rx. Why would it desense with one ant and not the other ant? I know the idea behind the yagi and the mobile ant. But they both have rf going vertical. I need to have minimal separation without it talking to itself. Your ideas? Thank you. Rod Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] Antenna Separation
The rx ant at the top and the tx ant at the bottom, about 12' to 14' separation. The system would talk to itself. I removed the tx ant and replaced with a 4 ele yagi - works good. I need a omni ant for both rx and tx. I have an isolator on the tx and a Bp cavity and a circulator on the rx. Why would it desense with one ant and not the other ant? I know the idea behind the yagi and the mobile ant. But they both have rf going vertical. I need to have minimal separation without it talking to itself. Your ideas? Thank you. The patterns on completely different on the vertical vs. the yagi. If you are stuck with this situation which is not an optimum solution, you might consider inverting the bottom antenna. I've been able to shorten the vertical separation require between the two antennas like this by turning the bottom one upside down. Good Luck! N7HQR Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Antenna Separation
You could just buy two pass filters. number one to pass only the transmitter and installed on the transmitter. Number two would be a pass filter on the receiver tuned to the receiver this will stop your problem. 73 Russ, - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sunday, January 16, 2005 4:06 PM Subject: Re: [Repeater-Builder] Antenna Separation Eric, I stand corrected. It is not a circulator, but a DCI Band Pass Filter. The local radio repair shop I deal with called it a preselector. So it sounds like what I need to due is look for a duplexer for one antenna. The repeater is 15 watts, will do 40, but I wanted it less than 1/2 power. Rod Rod, I put some typical numbers into my CommShop for Windows program and came up with some recommendations that may surprise you. Assuming a 25 watt GM300 and 0.35 microvolt sensitivity, the program recommends 84.21 dB of isolation. This can be achieved with two identical antennas, in line with each other and separated vertically by 169 feet. A 40 watt radio calls for 86.25 dB of isolation or a vertical separation of 191 feet. These numbers do not consider all of the factors that might affect the outcome, and are based on zero desense. A separation of less than one-tenth of the recommended separation is guaranteed to result in major desense. I am surprised that it works at all. A bandpass cavity on the receiver certainly is a good idea, and it may explain your relative success, but I don't understand the use of a circulator on the receiver. Please advise the make and model of this circulator, and how you have connected it. 73, Eric Lemmon WB6FLY [EMAIL PROTECTED] wrote: I am sure this has been asked before, but I did a search archive on the subject and came up with 0. I have a GR 300 repeater with no duplexer, so I need 2 antennas. I tried a Larson mobile antenna w/ the ground radials as the receive antenna and the same for the tx antenna. These are mounted on a Station Master type antenna tube (the guts were pulled out because it was untunable for 2 meters). The rx ant at the top and the tx ant at the bottom, about 12' to 14' separation. The system would talk to itself. I removed the tx ant and replaced with a 4 ele yagi - works good. I need a omni ant for both rx and tx. I have an isolator on the tx and a Bp cavity and a circulator on the rx. Why would it desense with one ant and not the other ant? I know the idea behind the yagi and the mobile ant. But they both have rf going vertical. I need to have minimal separation without it talking to itself. Your ideas? Thank you. Rod Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
