RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
I'm basing those isolation figures on a calculator I found online that asked for the gain of the antennas and the separation (horizontal or vertical) Re splitting the simplex: a circulator with the radio hooked to the input, the transmit chain on the standard output, and the receive chain feeding the load port is what I was thinking - a relay would do the job just as well, but would require changes to the PC based Packet Engine software to support flipping the relay before and after transmitting. I don't think that's a built in feature, and source code is not available. Re 4/5 ports: I have 3 transmit frequencies. 144.39, 145.05, and 145.25, and 3 receive frequencies. 144.39, 144.65, and 145.05 - if I keep transmit and receive on separate chains, I only need a 4 port splitter/combiner on each chain. if I go full out with all BP cavities, combined transmit/receive chain for the simplex rigs, and no circulators/isolators, I need a 5 port. If I understand the products correctly, a standard star coupler is just resistance on each port to balance the impedance presented, and there is no port to port isolation. I feel I would be better off with a Wilkinson at that point because it would give me some additional port to port isolation, and If I'm reading it right, for about the same insertion loss. I have approximately 18x18x60 without moving cans to the cargo bay. perhaps a little less - I'll have to measure - say enough for 9 5-6 cans, or as many as 18 of the smaller cans that I have - the cans I have are a mix from 5 to 8, with the idea that the larger cans would be used where I needed sharper skirts, on the close spaced frequencies. The key here is the height of the cans. if they are short enough (less than 30 total including tuning rod), I can do 2 banks, facing different sides of the trailer.. doubling the number of cans I can pack in. Only one of the cans I have so far exceeds that spec, and only by a little.. once its tuned it may be less than the 30 max, or I can trade it off with a shorter can on the other side to make up the difference. I would prefer to keep all the cans on one side if possible, but it is looking more and more like it will not be, so I'm willing to give up some space in the power electronics bay to make space for more cans. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Tuesday, October 23, 2007 6:43 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget If I do two antennas, the best I can do is about 30db isolation (30ft separation, 6db multi-bay folded dipole antenna on bottom, 9db 2m/440 base station antenna on top), If you can get 30 feet of separation, you'll get more than 30 dB of isolation. More like 50 dB on VHF, 60 dB or more on UHF as a guess. Going to split the simplex radios with a circulator on each.. Maybe I'm missing something. I was talking about splitting the transmitter and receiver apart so you could combine the transmitters separate from the receivers if you were going to use hybrids as the primary means of combining. I've done some checking around for stars.. haven't found any - I'm combining three transmitters - so 4 ports ?? You have four frequencies (144.39, 144.65, 145.05, 145.25), plus an antenna. Five ports. got some vendors or links I can look at Try Delta Electronics, Pasternak, maybe Kings. A 4-port cross is easy to find. It's easy to build stars with more ports in a small die-cast box (the ideal-sized box would make all of the center pins of the connectors coincident). If I can use the star to eliminate hybrid couplers, that would be great :-) that would leave me with a 2 stage isolator and one or more cans per transmitter. Split antennas is, by far, the best way to go. Your biggest problem is the 145.05 Tx/Rx versus 145.250 Tx. I'd be inclined to start doing the analysis assuming 145.05 is on its own antenna, with the remaining frequencies three-wayed on another antenna using conventional cavity-ferrite combining. I don't have t-pass cavities, but since I'm still acquiring cavities, I can get them if warranted. I've got 4 regular band pass cans right now, 2 more on ebay I'm trying to get, and a 6 can helical BR/BR duplexer that I can use for a really deep notch if I need it somewhere (or will become part of the receiver filters if I decide to stack BR filters for receive, as per my previous post) A helical pass/reject duplexer isn't going to help with the close spacings involved. You might get lucky and be able to it to get some filtering between the extremes (144.39 vs 145.25), but otherwise, the notches aren't going to be sharp enough to avoid degrading the frequencies in between. Have you swept it to really see what its performance is like (both transmission and reflection)? How much room do you have? --- Jeff
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
Keith: A very good point - and multiplied since there will be 3 receivers involved :-) Perhaps a good reason to stick with 3 cans per receiver, instead of 2, since that will give me the same protection any standard duplexer would, and even more isolation when things are working right, at the cost of a little more insertion loss. Depending on the insertion loss of the cavities in the receive chain - I'm looking at 6 to 9db of loss between the splitter and the cavity filters. It makes putting a preamp before the receive splitter an interesting possibility, to make up some of the losses further down the chain, at the cost of intermod in the preamp, which might be covered with a single band pass filter right before the preamp (1mhz wide, centered on my receive window). though that wont stop intermod with my own transmit signals. Still, if the antenna were to go bad, its more likely the preamp would smoke before enough got through to smoke the radios :-) _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Keith McQueen Sent: Tuesday, October 23, 2007 12:11 AM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget The danger I see with this is when your antenna goes bad (and they all do eventually), your receiver will be hit with the full reflected power of the PA almost certainly turning it into a smoldering doorstop. Keith McQueen 801-224-9460 [EMAIL PROTECTED] -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Barrett Sent: Monday, October 22, 2007 7:47 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget An isolator wont cause intermod, but it may cause harmonics. Commercial installations usually use either a harmonic filter and 3db hybrid coupler, or a special type of band pass cavity to couple the output from the isolator to the feed line. (This info from an RX TX application note on transmitter combiners) I'm proposing a novel application of the circulator (an isolator without the dummy load on one port).. Instead of the dummy load, the 3rd port feeds the receiver chain. the transmit chain will still use more or less conventional combining techniques to merge the signals from the 3 transmitters. the output from the transmitter combiner goes to the input of an additional circulator, the circulator output goes to the antenna as you would normally expect for an isolator, and the load port goes to the receive chain instead of a dummy load. Since the path from the transmit chain port to the receive chain port is reversed compared to the normal signal flow in a circulator, it will incur 20-30db of loss, depending on the circulator specs. So long as the antenna is well matched, there will be minimum reflected power fed back into the receive chain. My window for all the transmitters and receivers is less than 1mhz, so matching the antenna shouldn't be a huge problem. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Monday, October 22, 2007 8:19 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget I am not sure why an isolator would cause intermod. Usually there are not active or non-linear components in them and they are often used to prevent intermod by preventing outside signals from coming in thru the feedline into the transmitter. In the past commerical sites would often require an isolator for this reason with strong transmitters close by. In better repeater equipment an isolator was built in. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] mailto:jd0%40broadsci.com com Date: 2007/10/22 Mon PM 07:27:09 CDT To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget This isn't guessing - its called RESEARCH When I said guessing, I was talking about quantifying the performance of your radios rather than guessing how much isolation you need. In other words, make measurements to actually determine how much noise supression and carrier attenuation you need using the actual frequencies involved. Once you know how much isolation you truly need, then you can work backwards from there to determine the filtering requirements. I still think using an isolator is going to cause you new problems with respect to IM into your receivers unless you have adequate filtering between the isolator and antenna, which I believe you have no way of acheiving if I'm understanding your layout right (i.e. isolator is connected directly to the antenna with nothing in between save for a harmonic filter). --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
OK - Here are my requirements for the transmit chain. minimal physical space and minimal insertion loss :-) (ok - too bloody obvious) Tuning simplicity is also a factor. I'm combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25 Right now by best bet for minimal space is the hybrid coupler approach, but I pay in insertion loss. best for insertion loss is the T-Pass, but the T-Pass is starting to cut heavily into my available space --- I'm already looking at 6-9 cans on the receive side and would prefer something with NO cans on the transmit side. Despite the space issues I'm still considering the T-Pass because of the improved spurious signal suppression. Getting the cans is another issue - could I use a regular band pass can with a coax T rather than an actual T-Pass can ?? Can you list out some of the other options that I might be able to squeeze onto my trailer ?? _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Monday, October 22, 2007 9:41 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget Commercial installations usually use either a harmonic filter and 3db hybrid coupler, or a special type of band pass cavity to couple the output from the isolator to the feed line. (This info from an RX TX application note on transmitter combiners) Well, that's just two out of a myriad of ways of combining, duplexing, multicoupling, etc. Hybrid-ferrite and TX-RX's T-pass are by no means the only two ways of combining transmitters.
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
OK - Here are my requirements for the transmit chain. minimal physical space and minimal insertion loss :-) (ok - too bloody obvious) Tuning simplicity is also a factor. I'm combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25 Before we get to what hardware to use, we still need to quantify how much isolation you really need between each transmitter and receiver. I'll throw out real rough numbers but they really need to be determined ahead of time: 144.39 Tx noise supression at 145.05 (660 kHz) - 80 dB 144.39 Tx noise supression at 144.65 (260 kHz) - 105 dB 145.05 Tx noise supression at 144.39 (660 kHz) - 80 dB 145.05 Tx noise supression at 144.65 (400 kHz) - 95 dB 145.25 Tx noise supression at 144.39 (860 kHz) - 70 dB 145.25 Tx noise supression at 145.05 (200 kHz) - 110 dB 145.25 Tx noise supression at 144.65 (600 kHz) - 85 dB 144.39 carrier supression at 145.05 Rx (660 kHz) - 80 dB 144.39 carrier supression at 144.65 Rx (260 kHz) - 85 dB 145.05 carrier supression at 144.39 Rx (660 kHz) - 80 dB 145.05 carrier supression at 144.65 Rx (400 kHz) - 80 dB 145.25 carrier supression at 144.39 Rx (860 kHz) - 80 dB 145.25 carrier supression at 145.05 Rx (200 kHz) - 85 dB 145.25 carrier supression at 144.65 Rx (600 kHz) - 80 dB 144.39 Tx to/from 145.05 Tx - 60 dB 144.39 Tx to/from 145.25 Tx - 60 dB 145.05 Tx to/from 145.25 Tx - 60 dB From lowest to highest, it looks like this: 144.39 Tx/Rx --260 khz-- 144.65 Rx --400 kHz-- 145.05 Tx/Rx ---200 kHz-- 145.25 Tx Question 1: Are you locked in to a single antenna, or are two antennas a possibility? Question 2: If two antennas are a possibility, how much isolation can you reasonably expect to get between them? Question 3: Did you decide how you're going to split the simplex transmitters and receivers (digis)? Right now by best bet for minimal space is the hybrid coupler approach, but I pay in insertion loss. As a real rough estimate, you'd be looking at 10 dB or more insertion loss for two of the transmitters and 7 dB or more for the third once you factor in filter losses. If you're willing to take a 7 dB hit on one transmitter alone, you'd be better off putting up two half-height antennas (3 dB gain reduction) which will buy you 20-30 dB of isolation right there, and you'd be almost guaranteed to come out better in ERP and sensitivity even including the 3 dB antenna gain hit. loss is the T-Pass, but the T-Pass is starting to cut heavily into my available space --- I'm already looking at 6-9 cans on the receive side and would prefer something with NO cans on the transmit side. No cans on the transmit site - forget it. You've got 100 dB+ of noise supression to make up somehow. Despite the space issues I'm still considering the T-Pass because of the improved spurious signal suppression. Getting the cans is another issue - could I use a regular band pass can with a coax T rather than an actual T-Pass can ?? You could do a five-port star. If you don't already have cavities with T-pass style loops in them, there's no reason to try to build using that design. Can you list out some of the other options that I might be able to squeeze onto my trailer ?? What are the space limitations? --- Jeff
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
If I do two antennas, the best I can do is about 30db isolation (30ft separation, 6db multi-bay folded dipole antenna on bottom, 9db 2m/440 base station antenna on top), or I can get close to the same isolation with a circulator and one antenna.. so I don't see a difference there and one antenna really simplifies things. (plus gets more gain and height compared to the dipole array mounted low on the tower).. there is another issue, a 2nd antenna is at best a month away before I can slip it into the budget - I have the base antenna available now. Going to split the simplex radios with a circulator on each.. anything that leaks through from transmit to receive will be 30db down and have to get through the receive splitter and receive filters on the other receivers before it can be a problem. Also, non-mechanical so removes a potential point of failure !! I've done some checking around for stars.. haven't found any - I'm combining three transmitters - so 4 ports ?? got some vendors or links I can look at ?? If I can use the star to eliminate hybrid couplers, that would be great :-) that would leave me with a 2 stage isolator and one or more cans per transmitter. I don't have t-pass cavities, but since I'm still acquiring cavities, I can get them if warranted. I've got 4 regular band pass cans right now, 2 more on ebay I'm trying to get, and a 6 can helical BR/BR duplexer that I can use for a really deep notch if I need it somewhere (or will become part of the receiver filters if I decide to stack BR filters for receive, as per my previous post) _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Tuesday, October 23, 2007 4:37 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget OK - Here are my requirements for the transmit chain. minimal physical space and minimal insertion loss :-) (ok - too bloody obvious) Tuning simplicity is also a factor. I'm combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25 Before we get to what hardware to use, we still need to quantify how much isolation you really need between each transmitter and receiver. I'll throw out real rough numbers but they really need to be determined ahead of time: 144.39 Tx noise supression at 145.05 (660 kHz) - 80 dB 144.39 Tx noise supression at 144.65 (260 kHz) - 105 dB 145.05 Tx noise supression at 144.39 (660 kHz) - 80 dB 145.05 Tx noise supression at 144.65 (400 kHz) - 95 dB 145.25 Tx noise supression at 144.39 (860 kHz) - 70 dB 145.25 Tx noise supression at 145.05 (200 kHz) - 110 dB 145.25 Tx noise supression at 144.65 (600 kHz) - 85 dB 144.39 carrier supression at 145.05 Rx (660 kHz) - 80 dB 144.39 carrier supression at 144.65 Rx (260 kHz) - 85 dB 145.05 carrier supression at 144.39 Rx (660 kHz) - 80 dB 145.05 carrier supression at 144.65 Rx (400 kHz) - 80 dB 145.25 carrier supression at 144.39 Rx (860 kHz) - 80 dB 145.25 carrier supression at 145.05 Rx (200 kHz) - 85 dB 145.25 carrier supression at 144.65 Rx (600 kHz) - 80 dB 144.39 Tx to/from 145.05 Tx - 60 dB 144.39 Tx to/from 145.25 Tx - 60 dB 145.05 Tx to/from 145.25 Tx - 60 dB From lowest to highest, it looks like this: 144.39 Tx/Rx --260 khz-- 144.65 Rx --400 kHz-- 145.05 Tx/Rx ---200 kHz-- 145.25 Tx Question 1: Are you locked in to a single antenna, or are two antennas a possibility? Question 2: If two antennas are a possibility, how much isolation can you reasonably expect to get between them? Question 3: Did you decide how you're going to split the simplex transmitters and receivers (digis)? Right now by best bet for minimal space is the hybrid coupler approach, but I pay in insertion loss. As a real rough estimate, you'd be looking at 10 dB or more insertion loss for two of the transmitters and 7 dB or more for the third once you factor in filter losses. If you're willing to take a 7 dB hit on one transmitter alone, you'd be better off putting up two half-height antennas (3 dB gain reduction) which will buy you 20-30 dB of isolation right there, and you'd be almost guaranteed to come out better in ERP and sensitivity even including the 3 dB antenna gain hit. loss is the T-Pass, but the T-Pass is starting to cut heavily into my available space --- I'm already looking at 6-9 cans on the receive side and would prefer something with NO cans on the transmit side. No cans on the transmit site - forget it. You've got 100 dB+ of noise supression to make up somehow. Despite the space issues I'm still considering the T-Pass because of the improved spurious signal suppression. Getting the cans is another issue - could I use a regular band pass can with a coax T rather than an actual T-Pass can ?? You could do a five-port star. If you don't already have cavities with T-pass style loops in them, there's no reason to try to build using that design. Can you list out some of the other options
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
If I do two antennas, the best I can do is about 30db isolation (30ft separation, 6db multi-bay folded dipole antenna on bottom, 9db 2m/440 base station antenna on top), If you can get 30 feet of separation, you'll get more than 30 dB of isolation. More like 50 dB on VHF, 60 dB or more on UHF as a guess. Going to split the simplex radios with a circulator on each.. Maybe I'm missing something. I was talking about splitting the transmitter and receiver apart so you could combine the transmitters separate from the receivers if you were going to use hybrids as the primary means of combining. I've done some checking around for stars.. haven't found any - I'm combining three transmitters - so 4 ports ?? You have four frequencies (144.39, 144.65, 145.05, 145.25), plus an antenna. Five ports. got some vendors or links I can look at Try Delta Electronics, Pasternak, maybe Kings. A 4-port cross is easy to find. It's easy to build stars with more ports in a small die-cast box (the ideal-sized box would make all of the center pins of the connectors coincident). If I can use the star to eliminate hybrid couplers, that would be great :-) that would leave me with a 2 stage isolator and one or more cans per transmitter. Split antennas is, by far, the best way to go. Your biggest problem is the 145.05 Tx/Rx versus 145.250 Tx. I'd be inclined to start doing the analysis assuming 145.05 is on its own antenna, with the remaining frequencies three-wayed on another antenna using conventional cavity-ferrite combining. I don't have t-pass cavities, but since I'm still acquiring cavities, I can get them if warranted. I've got 4 regular band pass cans right now, 2 more on ebay I'm trying to get, and a 6 can helical BR/BR duplexer that I can use for a really deep notch if I need it somewhere (or will become part of the receiver filters if I decide to stack BR filters for receive, as per my previous post) A helical pass/reject duplexer isn't going to help with the close spacings involved. You might get lucky and be able to it to get some filtering between the extremes (144.39 vs 145.25), but otherwise, the notches aren't going to be sharp enough to avoid degrading the frequencies in between. Have you swept it to really see what its performance is like (both transmission and reflection)? How much room do you have? --- Jeff
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
An isolator wont cause intermod, but it may cause harmonics. Commercial installations usually use either a harmonic filter and 3db hybrid coupler, or a special type of band pass cavity to couple the output from the isolator to the feed line. (This info from an RX TX application note on transmitter combiners) I'm proposing a novel application of the circulator (an isolator without the dummy load on one port).. Instead of the dummy load, the 3rd port feeds the receiver chain. the transmit chain will still use more or less conventional combining techniques to merge the signals from the 3 transmitters. the output from the transmitter combiner goes to the input of an additional circulator, the circulator output goes to the antenna as you would normally expect for an isolator, and the load port goes to the receive chain instead of a dummy load. Since the path from the transmit chain port to the receive chain port is reversed compared to the normal signal flow in a circulator, it will incur 20-30db of loss, depending on the circulator specs. So long as the antenna is well matched, there will be minimum reflected power fed back into the receive chain. My window for all the transmitters and receivers is less than 1mhz, so matching the antenna shouldn't be a huge problem. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Monday, October 22, 2007 8:19 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget I am not sure why an isolator would cause intermod. Usually there are not active or non-linear components in them and they are often used to prevent intermod by preventing outside signals from coming in thru the feedline into the transmitter. In the past commerical sites would often require an isolator for this reason with strong transmitters close by. In better repeater equipment an isolator was built in. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] mailto:jd0%40broadsci.com com Date: 2007/10/22 Mon PM 07:27:09 CDT To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget This isn't guessing - its called RESEARCH When I said guessing, I was talking about quantifying the performance of your radios rather than guessing how much isolation you need. In other words, make measurements to actually determine how much noise supression and carrier attenuation you need using the actual frequencies involved. Once you know how much isolation you truly need, then you can work backwards from there to determine the filtering requirements. I still think using an isolator is going to cause you new problems with respect to IM into your receivers unless you have adequate filtering between the isolator and antenna, which I believe you have no way of acheiving if I'm understanding your layout right (i.e. isolator is connected directly to the antenna with nothing in between save for a harmonic filter). --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
I am not sure why an isolator would cause intermod. Usually there are not active or non-linear components in them An isolator IS a non-linear device. and they are often used to prevent intermod by preventing outside signals from coming in thru the feedline into the transmitter. As a nonlinear device, they will naturally generate harmonics on their own, and likewise act as mixers (however lossy), which is why filtering after an isolator is necessary. In the past commerical sites would often require an isolator for this reason with strong transmitters close by. In better repeater equipment an isolator was built in. Yes. The isolator isolates the transmitter from the antenna by diverting incoming (from the antenna) RF into the reject load rather than letting it get back into the transmitter as a way of preventing IM from occuring. But in some instances, that's more of an added bonus than the real reason the isolator was built in to some stations - to protect the PA from anomalies that would cause high VSWR that could damage the PA or lead to instability issues. My concern, in the instant case, is that when the isolator is carrying high-level RF from the transmitter will mix with other signals coming back down from the antenna. I might try a two-tone IM text on an isolator to get a handle on what might be expected. --- Jeff
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
An isolator wont cause intermod, but it may cause harmonics. How so? What phenomenon occurs in a ferrite circulator that creates harmonics but won't generate IMD? Commercial installations usually use either a harmonic filter and 3db hybrid coupler, or a special type of band pass cavity to couple the output from the isolator to the feed line. (This info from an RX TX application note on transmitter combiners) Well, that's just two out of a myriad of ways of combining, duplexing, multicoupling, etc. Hybrid-ferrite and TX-RX's T-pass are by no means the only two ways of combining transmitters. I'm proposing a novel application of the circulator (an isolator without the dummy load on one port).. Yes, I know what you're trying to do, and it's nothing new. UHF Micor mobiles have an isolator in the antenna network that routes received RF through the isolator to the receiver when the transmitter is not keyed. I forget how the full-duplex Micor med radios were set up; I believe the antenna network in those radios was different, maybe somebody else remembers. Circulators are used in the manner you're contemplating in duplex microwave systems all the time, but with the addition of filters in both paths. the transmit chain will still use more or less conventional combining techniques to merge the signals from the 3 transmitters. the output from the transmitter combiner goes to the input of an additional circulator, the circulator output goes to the antenna as you would normally expect for an isolator, and the load port goes to the receive chain instead of a dummy load In your example, you will have three transmitter carriers going through a common isolator. That's where I think you may have spectral problems show up due to IM amidst the high-level carriers. Since the path from the transmit chain port to the receive chain port is reversed compared to the normal signal flow in a circulator, it will incur 20-30db of loss, depending on the circulator specs. It's not only a function of the circulator's inherent directivity spec; the usable isolation is likely going to be dominated by the mismatch at the antenna port as I said before. Even if you match well when you install it, feedline phase change with temperature, feedpoint Z varying with weather conditions, and all of the other uncertainties and uncontrollables in the antenna system are only going to degrade the match (and therefore isolation) over time. --- Jeff
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
At 07:41 PM 10/22/07, you wrote: I'm proposing a novel application of the circulator (an isolator without the dummy load on one port).. Yes, I know what you're trying to do, and it's nothing new. UHF Micor mobiles have an isolator in the antenna network that routes received RF through the isolator to the receiver when the transmitter is not keyed. I forget how the full-duplex Micor med radios were set up; I believe the antenna network in those radios was different, maybe somebody else remembers. (rest deleted) The original med radio manual is on the Micor page at repeater-builder as a PDF: Emergency Medical Systems Duplex / Repeater UHF Mobile Radio manual supplement PDF file courtesy of K9ROD http://www.repeater-builder.com/micor/pdf/micor-ems-uhf-manual.pdf This is the no-longer-available manual supplement for the full-duplex dual-receiver repeating ambulance radio model Q2033 and Q1853. Note that you need the regular UHF mobile manual 68-81015E70 to go along with it. Note this is a 16.6 MB file
RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget
The danger I see with this is when your antenna goes bad (and they all do eventually), your receiver will be hit with the full reflected power of the PA almost certainly turning it into a smoldering doorstop. Keith McQueen 801-224-9460 [EMAIL PROTECTED] -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Barrett Sent: Monday, October 22, 2007 7:47 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget An isolator wont cause intermod, but it may cause harmonics. Commercial installations usually use either a harmonic filter and 3db hybrid coupler, or a special type of band pass cavity to couple the output from the isolator to the feed line. (This info from an RX TX application note on transmitter combiners) I'm proposing a novel application of the circulator (an isolator without the dummy load on one port).. Instead of the dummy load, the 3rd port feeds the receiver chain. the transmit chain will still use more or less conventional combining techniques to merge the signals from the 3 transmitters. the output from the transmitter combiner goes to the input of an additional circulator, the circulator output goes to the antenna as you would normally expect for an isolator, and the load port goes to the receive chain instead of a dummy load. Since the path from the transmit chain port to the receive chain port is reversed compared to the normal signal flow in a circulator, it will incur 20-30db of loss, depending on the circulator specs. So long as the antenna is well matched, there will be minimum reflected power fed back into the receive chain. My window for all the transmitters and receivers is less than 1mhz, so matching the antenna shouldn't be a huge problem. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Monday, October 22, 2007 8:19 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget I am not sure why an isolator would cause intermod. Usually there are not active or non-linear components in them and they are often used to prevent intermod by preventing outside signals from coming in thru the feedline into the transmitter. In the past commerical sites would often require an isolator for this reason with strong transmitters close by. In better repeater equipment an isolator was built in. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] mailto:jd0%40broadsci.com com Date: 2007/10/22 Mon PM 07:27:09 CDT To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget This isn't guessing - its called RESEARCH When I said guessing, I was talking about quantifying the performance of your radios rather than guessing how much isolation you need. In other words, make measurements to actually determine how much noise supression and carrier attenuation you need using the actual frequencies involved. Once you know how much isolation you truly need, then you can work backwards from there to determine the filtering requirements. I still think using an isolator is going to cause you new problems with respect to IM into your receivers unless you have adequate filtering between the isolator and antenna, which I believe you have no way of acheiving if I'm understanding your layout right (i.e. isolator is connected directly to the antenna with nothing in between save for a harmonic filter). --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
