Re: [Repeater-Builder] Coax length between added cavity and duplexer
Ron Wright wrote: Nate, A local, in Tampa, FL, high profile repeater has a similar problem. They are on 2 meters along side a 800 MHz repeater which gives them interference. They have to live with it. However, it is weak and they PL'd their repeater. Since weak the users can over ride and the PL only allows the users to bring up the machine. Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy rx! Or the antennas are REALLY close! -- Jim Barbour WD8CHL
Re: Re: [Repeater-Builder] Coax length between added cavity and duplexer
Nate, A local, in Tampa, FL, high profile repeater has a similar problem. They are on 2 meters along side a 800 MHz repeater which gives them interference. They have to live with it. However, it is weak and they PL'd their repeater. Since weak the users can over ride and the PL only allows the users to bring up the machine. As so many of us Hams do, getting on sites for free, we have to put up with some problems. Of course it does depend on the survarity of the problem. 73, ron, n9ee/r From: Nate Bargmann [EMAIL PROTECTED] Date: 2007/07/26 Thu PM 01:09:56 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer * Steve S. Bosshard (NU5D) [EMAIL PROTECTED] [2007 Jul 26 13:05 -0500]: You could always try and scrap the front end from a thrashed M2 mobile - kinda lossy but can be used as a preselector - Also even a 3 dB. attenuator might help against overload at the cost of 3dB. in RX sen. Out of curiosity, what kind of repeater are you using? Probably said in an earlier post - don't remember. It is a TKR-720. Probably not the best choice for this site. ;-) Again, it's not my system and there are some politics with getting involved to much that I'd rather avoid. So, at this point we're helping as we can. Thanks for all the ideas. Many I've seen or even tried in the pastand perhaps forgot. :-D 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: Re: [Repeater-Builder] Coax length between added cavity and duplexer
That would be intermod, but not intermod generated inside ones own equipment. If there is intermod mixing on a different or far away commerical site finding it would be hard, but getting it solved might be even harder. Depends on the owner of the other system. 300 W pager txs for years have caused problems, but since no problem to the pager company they often don't care. It is just spending money to solve someone elses problem. 73, ron, n9ee/r From: [EMAIL PROTECTED] Date: 2007/07/26 Thu PM 01:38:13 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer And if the mixing is someone else's PA with some outside RF energy - that's notproperly characterized as intermod when it ends up on your input?  In a message dated 7/26/2007 11:30:47 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes:---Intermod means there is mixing in YOUR PA with some outside RF energy. Could be, could be not. You need to run all the frequencies used at your site in order to identify any possible 2nd, 3rd, 4th and so on products. Or it might be a straight mix. BTW, what do you mean by interference? Are you hearing other signals or is is something else? (knowing the 'sound' of the interference generally goes a long way at identifying it)  Get a sneak peek of the all-new AOL.com. Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: [Repeater-Builder] Coax length between added cavity and duplexer
Jim, I agree that the 800 MHz repeater's carrier frequency is probably too far from the 2m repeater's input to cause a problem, but there is also the possibility that the 800MHz transmitter's exciter is causing the problem. A case in point: An older 800 MHz repeater was turned on at the same site as a local 2m repeater, and immediately caused major interference. It turned out that the exciter was radiating at 1/6 of the 868 MHz carrier, since that model transmitter used a VHF exciter followed by a doubler and a tripler. The exciter leakage was just a few kHz away from the 2m input, and it severely interfered with the 2m repeater's reception. The leakage occurred because a careless tech left off one shield and did not install all of the screws in another shield. Once the 800MHz machine was properly buttoned up, the problem went away. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jim Sent: Friday, July 27, 2007 8:34 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer SNIP Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy rx! Or the antennas are REALLY close! -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Coax length between added cavity and duplexer
W5AC at Texas AM has a 2M repeater on 146.820 co-located with an 800 Mhz PST. The 146.820 transmitter mixes with one of the 800 mhz transmitters and has a direct hit on 146.220. They use split channel guard tones because if in and out tone were the same, the transmitter mix would open the receiver. They could have left tone off the transmitter, but then the co-channel 82 repeaters would be an issue to folks listening. The ham repeater is a MastrII. Seems like they moved the 2M repeater from Kyle Stadium to Rudder Hall and the problem lessened but did not entirely go away. PS - I called Lloyd Alcorn this morning but got his answering machine - will call back later in the day. Steve NU5D. Jim wrote: Ron Wright wrote: Nate, A local, in Tampa, FL, high profile repeater has a similar problem. They are on 2 meters along side a 800 MHz repeater which gives them interference. They have to live with it. However, it is weak and they PL'd their repeater. Since weak the users can over ride and the PL only allows the users to bring up the machine. Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy rx! Or the antennas are REALLY close! -- Ham Radio Spoken Here !!! NU5D EM11 http://www.qrz.com/callsign/NU5D Nickel Under 5 Dollars
[Repeater-Builder] Coax length between added cavity and duplexer - test results
I performed an experiment per previous discussion. The results are available at: http://www.broadsci.com/900.pdf Apologies in advance for the terse verbage and any typos; I was trying to get it done quickly between real work projects. Feedback would be greatly appreciated. --- Jeff
Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...
Jeff Just a dynamite presentation. Thanks for the effort. BTW, where are you (The analysis is dated July 29) Bruce K7IJ In a message dated 7/27/2007 10:19:02 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: I performed an experiment per previous discussion. The results are available at: _http://www.broadscihttp://wwhtt_ (http://www.broadsci.com/900.pdf) Apologies in advance for the terse verbage and any typos; I was trying to get it done quickly between real work projects. Feedback would be greatly appreciated. --- Jeff ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour
Re: [Repeater-Builder] Coax length between added cavity and duplexer - test results
Very nicely done, Jeff! At least as good as some manufacturers' reports, and color too! George - Original Message - From: Jeff DePolo [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, July 27, 2007 11:54 AM Subject: [Repeater-Builder] Coax length between added cavity and duplexer - test results I performed an experiment per previous discussion. The results are available at: http://www.broadsci.com/900.pdf Apologies in advance for the terse verbage and any typos; I was trying to get it done quickly between real work projects. Feedback would be greatly appreciated. --- Jeff
Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...
Maybe his computer is running on UTC? - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, July 27, 2007 5:16 PM Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r... Jeff Just a dynamite presentation. Thanks for the effort. BTW, where are you (The analysis is dated July 29) Bruce K7IJ
RE: [Repeater-Builder] Coax length between added cavity and duplexer - test r...
Just a dynamite presentation. Thanks for the effort. BTW, where are you (The analysis is dated July 29) I'm caught in a time warp in Philadelphia.
Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...
Understood. But take comfort. You're not alone. Report is that everybody in Philadelphia is warped. In a message dated 7/27/2007 6:05:10 P.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: Just a dynamite presentation. Thanks for the effort. BTW, where are you (The analysis is dated July 29) I'm caught in a time warp in Philadelphia. ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour
Re: [Repeater-Builder] Coax length between added cavity and duplexer - test results
Cannot display the webpage is what I get. Chuck - Original Message - From: Jeff DePolo [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, July 27, 2007 12:54 PM Subject: [Repeater-Builder] Coax length between added cavity and duplexer - test results I performed an experiment per previous discussion. The results are available at: http://www.broadsci.com/900.pdf Apologies in advance for the terse verbage and any typos; I was trying to get it done quickly between real work projects. Feedback would be greatly appreciated. --- Jeff Yahoo! Groups Links
Re: [Repeater-Builder] Coax length between added cavity and duplexer
* [EMAIL PROTECTED] [EMAIL PROTECTED] [2007 Jul 26 12:14 -0500]: Thanks for all of your input. I'm learning more as I go along. I did not get a chance to performance check the RX on site. It just happened that we were able to stop by the site a week ago and see what we were up against. Having said that, I think Skipp's point is well taken - if the junk is on channel, an additional pass cavity isn't going to eliminate it. BTW, are you using an isolator on the TX? Right now, no. There isn't one handy and since there are only a couple of active hams in the county, I don't know whether they're willing to plop down a few hundred bucks to try. But, you never know! There is also some amount of politics involved here as the repeater is actually owned by the county, as I understand it now. Fortunately, the interference is not constant nor really consistent. Hopefully, we can arrange a meet out there again and I can gather more information and do some tests. 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org
Re: [Repeater-Builder] Coax length between added cavity and duplexer
Gary Schafer wrote: Intermod IS the result of mixing. The mixing can take place in your receiver (commonly called receiver intermod). Mixing can take place in your own transmitter, which generates a product that falls on your receive frequency(or on someone else's) or the mixing can take place in someone else's transmitter with the resulting product falling on your receive frequency. It is all intermodulation. i.e. the result of mixing of two or more frequencies in a non linear device. ...like a rusty joint on a tower... ...or a guy wire... ...or a fence... -- Jim Barbour WD8CHL
RE: [Repeater-Builder] Coax length between added cavity and duplexer
Now, from a perspective of impedance matching, wouldn't it make sense to use a circulator at the input of the reciever so that it is also matched to 50-ohms? At first glance it might seem like a good idea, until you consider that circulators aren't linear devices; they can produce mix products and harmonics within. At low receive signal levels this isn't a problem because the IM products are substantially lower in amplitude than the fundamentals, but in the presence of one or more strong signals, it could be an issue... --- Jeff
Re: [Repeater-Builder] Coax length between added cavity and duplexer
On Thu, 26 Jul 2007, Ken Arck wrote: Firstly, in the case of your additional bandpass cavity - if cavities are properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make one bit of difference. The problem most people have with proper cavity/duplexer tuning is that they don't maintain a 50 ohm load on ALL ports when they tune 'em. So when they're placed into service, the port impedances are different and the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER tune either without at least a 3 dB 50 ohm pad on each of the ports. From your description, I'm willing to bet you didn't use pads :-) Now, from a perspective of impedance matching, wouldn't it make sense to use a circulator at the input of the reciever so that it is also matched to 50-ohms? rf - circulator - rx | - dummy load ? Since we know that some RXs aren't 50-ohms, nor are some TXs. I'm looking at this strictly from the point of view of matched impedances. -- Kris Kirby, KE4AHR [EMAIL PROTECTED] * WAR IS PEACE * FREEDOM IS SLAVERY * * IGNORANCE IS STRENGTH * KETCHUP IS * * A VEGETABLE *
Re: [Repeater-Builder] Coax length between added cavity and duplexer
- Original Message - From: Jeff DePolo [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Thursday, July 26, 2007 8:50 PM Subject: RE: [Repeater-Builder] Coax length between added cavity and duplexer [snip] But that doesn't even compare to the side-arm I saw made out of pine 2x4's... --- Jeff I've never seen the joints between 2x4's act as diodes;-) George
Re: [Repeater-Builder] Coax length between added cavity and duplexer
Hey, I thought I was the only one that ran in to the 2X4 cross arms.
RE: [Repeater-Builder] Coax length between added cavity and duplexer
...like a rusty joint on a tower... ...or a guy wire... ...or a fence... One of my favorites comes to mind. I was working a tower (somewhere in Virginia if I remember right), and there was a side-arm mount that had hardware on it that was too big for the tower legs, so as shims, the tower crew had stuck a crescent wrench behind the upper U-bolt and a pair of vice grips behind the lower U-bolt to make up the difference. I don't know how long they were up there, but the rust stains ran about 20' down the tower leg... But that doesn't even compare to the side-arm I saw made out of pine 2x4's... --- Jeff
Re: [Repeater-Builder] Coax length between added cavity and duplexer
Nate, I see you received a lot of answers to your question, and I have not taken the time to read them all, but my answer is that it will probably not matter how long the coax is. Also, what you are doing sounds like a very reasonable approach to the problem and may very well fix it. Good luck. Dave BaughnDirector of EngineeringThe University of AlabamaCenter for Public Television and RadioWVUA/WUOA-TV WUAL/ WQPR/ WAPR FMBox 870150195 Reese Phifer Hall, 901 University Blvd.Tuscaloosa, Alabama 35487205.348.8622 cell 205.310.8798[EMAIL PROTECTED] KX4I Nate Bargmann [EMAIL PROTECTED] 7/26/2007 7:09 AM I'm helping a club in the next county get their repeater workingbetter. A couple of weeks ago they brought the RF unit (TKR-720) overand we (KC0MLS, K0BYK, and myself) checked it out. The PA transistorrequired soldering and after that everything checked out well.Next we checked out the duplexer, a Wacom BpBr set. Lacking a trackinggenerator, we used our ancient IFR-1200 and a reprogrammed Spectramobile radio and tuned the pass filters for best SINAD and the notchfilters for the poorest SINAD for their respective frequencies.After they put everything back on site, it all works well except thatthe local public safety is getting into the receiver intermintently. My first thought was intermod, but the various programs don't turn up amatch for the receiver's frequency.A week ago we were able to visit the site and tightened several looseconnectors on the other hardware in the site. Since then theinterference does seem to be less but is still present on occasion.Observations of the site revealed that the public safety and the club'srepeater antennas (DB-224 style, unsure of exact models) both share thetop of the tower and are broadside to each other and are maybe fourfeet apart at most. So now our thinking is that the problem may bereceiver overload. We set up a spare Celwave bandpass cavity that has about 2 dB ofinsertion loss and offers about 45 dB of insertion loss at the publicsafety's transmitter frequency. My question is whether the coax lengthis critical between the RX port of the Wacom duplexer and the inputport of the Celwave cavity? I plan to send along a length of RG-393(double shielded teflon coax) with the cavity. As far as I know, it isa random length. Should I cut it to something closer to 1/2wavelength? 3/4 WL?Thanks!73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully MicrosoftAmateur radio exams; ham radio; Linux info @ | free since January 1998.http://wwwqsl.net/n0nb/ | "Debian, the choice ofMy Kawasaki KZ-650 SR @ | a GNU generation!"http://www.networksplus.net/n0nb/ | http://www.debian.orgimage/gifimage/xxx
Re: [Repeater-Builder] Coax length between added cavity and duplexer
What do you think a half wave interconnect at some unwanted frequency is going to to the pass curve at the desired frequency? If your sole concern is rejection of an unwanted frequency, hey, there is even a more effective way to do it - cut the cable in half. n a message dated 7/26/2007 10:32:39 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: So ideally if you want the most rejection a cable that provides a half wave length at the unwanted frequency will reflect that low impedance provided by the cavity skirt to the next port in the system at that frequency. ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour
RE: [Repeater-Builder] Coax length between added cavity and duplexer
Cable lengths sometimes are critical and sometimes not, depending what you are trying to accomplish with the particular setup. In the case of interconnecting cables between notch cavities a critical length cable will provide more notch depth because it unloads the next cavity. In the case of using pass band cavities to make a combiner into a common junction the cable lengths are critical even though everything is running at 50 ohms. The off frequency skirt of the cavity provides a short at some frequency and that short needs to be transformed to a high impedance at the junction so as not to load the other devices. DUPLEXER TUNING: In this case proper duplexer tuning should make little if any difference in the interference problem noted. As long as there is no desense from his own transmitter the duplexer is doing what it can. A bp-br duplexer has little off frequency rejection (pass band rejection) compared to a pass cavity. The bp-br duplexer does provide a little pass band help but not as much as some people like to believe. The frequencies between the transmit and receive frequencies have the most rejection from pass band effects but outside of them there is little. As was stated he is getting interference from a public safety transmitter so it would fall outside the more protected part of the duplexer. An additional pass filter on the receiver would indeed provide more protection but 45 db sounds like a lot to expect from a pass filter unless the frequency is a long ways away. As Skip noted a notch cavity at that point may well provide more protection. More to the point of cable length, a pass filter actually looks like a notch filter at the unwanted frequency i.e. a low impedance at that frequency. So ideally if you want the most rejection a cable that provides a half wave length at the unwanted frequency will reflect that low impedance provided by the cavity skirt to the next port in the system at that frequency. In this case the difference will probably not be noticed for the trouble involved. With the public safety antenna right beside the repeater antenna there can be fundamental overload of the receiver so some form of additional protection may help. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ken Arck Sent: Thursday, July 26, 2007 9:40 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer Hi Nate Firstly, in the case of your additional bandpass cavity - if cavities are properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make one bit of difference. The problem most people have with proper cavity/duplexer tuning is that they don't maintain a 50 ohm load on ALL ports when they tune 'em. So when they're placed into service, the port impedances are different and the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER tune either without at least a 3 dB 50 ohm pad on each of the ports. From your description, I'm willing to bet you didn't use pads :-) My other comment (and in my humble opinion) is that if you're using a properly tuned BpBr duplexer on a low power repeater (the 720 is 25 watts, yes?) and you need additional cavities in the receive side, you've got bigger issue than simply needing an additional cavity. You didn't specify what the inteference is but have you done an intermod study of the site? IMHO, the additional cavity is a waste of time and effort until you identify the source of the interference (and made sure your duplexer is first properly tuned) Ken At 05:09 AM 7/26/2007, you wrote: I'm helping a club in the next county get their repeater working better. A couple of weeks ago they brought the RF unit (TKR-720) over and we (KC0MLS, K0BYK, and myself) checked it out. The PA transistor required soldering and after that everything checked out well. Next we checked out the duplexer, a Wacom BpBr set. Lacking a tracking generator, we used our ancient IFR-1200 and a reprogrammed Spectra mobile radio and tuned the pass filters for best SINAD and the notch filters for the poorest SINAD for their respective frequencies. After they put everything back on site, it all works well except that the local public safety is getting into the receiver intermintently. My first thought was intermod, but the various programs don't turn up a match for the receiver's frequency. A week ago we were able to visit the site and tightened several loose connectors on the other hardware in the site. Since then the interference does seem to be less but is still present on occasion. Observations of the site revealed that the public safety and the club's repeater antennas (DB-224 style, unsure of exact models) both share the top of the tower and are broadside to each other and are maybe four feet apart at most. So now our thinking is that the problem may be receiver overload. We set up a spare Celwave
RE: [Repeater-Builder] Coax length between added cavity and duplexer
Intermod IS the result of mixing. The mixing can take place in your receiver (commonly called receiver intermod). Mixing can take place in your own transmitter, which generates a product that falls on your receive frequency(or on someone else's) or the mixing can take place in someone else's transmitter with the resulting product falling on your receive frequency. It is all intermodulation. i.e. the result of mixing of two or more frequencies in a non linear device. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of Ken Arck Sent: Thursday, July 26, 2007 1:29 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer At 11:06 AM 7/26/2007, you wrote: Intermod means there is mixing in YOUR PA with some outside RF energy. I should probably clarify that intermod is an often misused term that has become a generic terms used to describe just about any type of received interference. Ya know, kinda like Klenex has become the name for any tissue. Intermod is a very specific type of phenomenon and for accuracy, should only be used to describe intermodulation issues and not mixes, adjacent channel interference, etc. (more of my 2 cents) Ken Yahoo! Groups Links
Re: [Repeater-Builder] Coax length between added cavity and duplexer
At 11:06 AM 7/26/2007, you wrote: Intermod means there is mixing in YOUR PA with some outside RF energy. I should probably clarify that intermod is an often misused term that has become a generic terms used to describe just about any type of received interference. Ya know, kinda like Klenex has become the name for any tissue. Intermod is a very specific type of phenomenon and for accuracy, should only be used to describe intermodulation issues and not mixes, adjacent channel interference, etc. (more of my 2 cents) Ken
Re: [Repeater-Builder] Coax length between added cavity and duplexer
At 11:06 AM 7/26/2007, you wrote: No, we didn't. The IFR does have a pad built into its generator output and the Motorola Spectra mobile is probably fairly close to 50 ohms. I have yet to see a receiver from anyone that is 50 ohms. Besides, you know what they say about close but no cigar, yes? :-) The interference is that the repeater is receiving the public safety transmitter very clearly which has led me to think intermod. This TKR-720 is running about 40 Watts. ---Intermod means there is mixing in YOUR PA with some outside RF energy. Could be, could be not. You need to run all the frequencies used at your site in order to identify any possible 2nd, 3rd, 4th and so on products. Or it might be a straight mix. BTW, what do you mean by interference? Are you hearing other signals or is is something else? (knowing the 'sound' of the interference generally goes a long way at identifying it) Ken
Re: [Repeater-Builder] Coax length between added cavity and duplexer
* Ken Arck [EMAIL PROTECTED] [2007 Jul 26 09:44 -0500]: Hi Nate Firstly, in the case of your additional bandpass cavity - if cavities are properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make one bit of difference. The problem most people have with proper cavity/duplexer tuning is that they don't maintain a 50 ohm load on ALL ports when they tune 'em. So when they're placed into service, the port impedances are different and the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER tune either without at least a 3 dB 50 ohm pad on each of the ports. From your description, I'm willing to bet you didn't use pads :-) No, we didn't. The IFR does have a pad built into its generator output and the Motorola Spectra mobile is probably fairly close to 50 ohms. We did check the Celwave cavity this morning using pads and noted no change in its tuing. Admittedly, the Celwave is a much different device than the Wacom BpBr. My other comment (and in my humble opinion) is that if you're using a properly tuned BpBr duplexer on a low power repeater (the 720 is 25 watts, yes?) and you need additional cavities in the receive side, you've got bigger issue than simply needing an additional cavity. You didn't specify what the inteference is but have you done an intermod study of the site? The interference is that the repeater is receiving the public safety transmitter very clearly which has led me to think intermod. This TKR-720 is running about 40 Watts. IMHO, the additional cavity is a waste of time and effort until you identify the source of the interference (and made sure your duplexer is first properly tuned) Right now it's the easiest approach to try and be installed by the ham over there on his schedule. See one of my other posts for the details of the site. 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org
Re: [Repeater-Builder] Coax length between added cavity and duplexer
You could always try and scrap the front end from a thrashed M2 mobile - kinda lossy but can be used as a preselector - Also even a 3 dB. attenuator might help against overload at the cost of 3dB. in RX sen. Out of curiosity, what kind of repeater are you using? Probably said in an earlier post - don't remember. 73, Steve www.bosshardradio.com Nate Bargmann wrote: * [EMAIL PROTECTED] [EMAIL PROTECTED] [2007 Jul 26 12:14 -0500]: Thanks for all of your input. I'm learning more as I go along. I did not get a chance to performance check the RX on site. It just happened that we were able to stop by the site a week ago and see what we were up against. -- Ham Radio Spoken Here !!! NU5D EM11 http://www.qrz.com/callsign/NU5D Nickel Under 5 Dollars
RE: [Repeater-Builder] Coax length between added cavity and duplexer
But that doesn't even compare to the side-arm I saw made out of pine 2x4's... --- Jeff I've never seen the joints between 2x4's act as diodes;-) Yeah, but just try explaining to your insurance carrier that the reason your antenna came through the roof of the transmitter shelter was because of termites...
Re: [Repeater-Builder] Coax length between added cavity and duplexer
Hi Nate Firstly, in the case of your additional bandpass cavity - if cavities are properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make one bit of difference. The problem most people have with proper cavity/duplexer tuning is that they don't maintain a 50 ohm load on ALL ports when they tune 'em. So when they're placed into service, the port impedances are different and the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER tune either without at least a 3 dB 50 ohm pad on each of the ports. From your description, I'm willing to bet you didn't use pads :-) My other comment (and in my humble opinion) is that if you're using a properly tuned BpBr duplexer on a low power repeater (the 720 is 25 watts, yes?) and you need additional cavities in the receive side, you've got bigger issue than simply needing an additional cavity. You didn't specify what the inteference is but have you done an intermod study of the site? IMHO, the additional cavity is a waste of time and effort until you identify the source of the interference (and made sure your duplexer is first properly tuned) Ken At 05:09 AM 7/26/2007, you wrote: I'm helping a club in the next county get their repeater working better. A couple of weeks ago they brought the RF unit (TKR-720) over and we (KC0MLS, K0BYK, and myself) checked it out. The PA transistor required soldering and after that everything checked out well. Next we checked out the duplexer, a Wacom BpBr set. Lacking a tracking generator, we used our ancient IFR-1200 and a reprogrammed Spectra mobile radio and tuned the pass filters for best SINAD and the notch filters for the poorest SINAD for their respective frequencies. After they put everything back on site, it all works well except that the local public safety is getting into the receiver intermintently. My first thought was intermod, but the various programs don't turn up a match for the receiver's frequency. A week ago we were able to visit the site and tightened several loose connectors on the other hardware in the site. Since then the interference does seem to be less but is still present on occasion. Observations of the site revealed that the public safety and the club's repeater antennas (DB-224 style, unsure of exact models) both share the top of the tower and are broadside to each other and are maybe four feet apart at most. So now our thinking is that the problem may be receiver overload. We set up a spare Celwave bandpass cavity that has about 2 dB of insertion loss and offers about 45 dB of insertion loss at the public safety's transmitter frequency. My question is whether the coax length is critical between the RX port of the Wacom duplexer and the input port of the Celwave cavity? I plan to send along a length of RG-393 (double shielded teflon coax) with the cavity. As far as I know, it is a random length. Should I cut it to something closer to 1/2 wavelength? 3/4 WL? Thanks! 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @ | a GNU generation! http://www.networksplus.net/n0nb/http://www.networksplus.net/n0nb/ | http://www.debian.org -- President and CTO - Arcom Communications Makers of repeater controllers and accessories. http://www.arcomcontrollers.com/ Authorized Dealers for Kenwood and Telewave and we offer complete repeater packages! AH6LE/R - IRLP Node 3000 http://www.irlp.net We don't just make 'em. We use 'em!
Re: [Repeater-Builder] Coax length between added cavity and duplexer
And if the mixing is someone else's PA with some outside RF energy - that's not properly characterized as intermod when it ends up on your input? In a message dated 7/26/2007 11:30:47 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: ---Intermod means there is mixing in YOUR PA with some outside RF energy. Could be, could be not. You need to run all the frequencies used at your site in order to identify any possible 2nd, 3rd, 4th and so on products. Or it might be a straight mix. BTW, what do you mean by interferenceby interferenceWBR? Are you hearing other signals o else? (knowing the 'sound' of the interference generally goes a long way at identifying it) ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour
Re: [Repeater-Builder] Coax length between added cavity and duplexer
* Steve S. Bosshard (NU5D) [EMAIL PROTECTED] [2007 Jul 26 13:05 -0500]: You could always try and scrap the front end from a thrashed M2 mobile - kinda lossy but can be used as a preselector - Also even a 3 dB. attenuator might help against overload at the cost of 3dB. in RX sen. Out of curiosity, what kind of repeater are you using? Probably said in an earlier post - don't remember. It is a TKR-720. Probably not the best choice for this site. ;-) Again, it's not my system and there are some politics with getting involved to much that I'd rather avoid. So, at this point we're helping as we can. Thanks for all the ideas. Many I've seen or even tried in the pastand perhaps forgot. :-D 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org
Re: [Repeater-Builder] Coax length between added cavity and duplexer
At 11:38 AM 7/26/2007, you wrote: And if the mixing is someone else's PA with some outside RF energy - that's not properly characterized as intermod when it ends up on your input? ---Good point, although I meant more it happening at that site than specifically in his PA. I guess technically it would intermod based but not necessarily being generated in his equipment. My main point was explained later - in that intermod seems to have become a generic term for all sorts of interference, from external mixes to front-end overloading. Ken
[Repeater-Builder] Coax length between added cavity and duplexer
I'm helping a club in the next county get their repeater working better. A couple of weeks ago they brought the RF unit (TKR-720) over and we (KC0MLS, K0BYK, and myself) checked it out. The PA transistor required soldering and after that everything checked out well. Next we checked out the duplexer, a Wacom BpBr set. Lacking a tracking generator, we used our ancient IFR-1200 and a reprogrammed Spectra mobile radio and tuned the pass filters for best SINAD and the notch filters for the poorest SINAD for their respective frequencies. After they put everything back on site, it all works well except that the local public safety is getting into the receiver intermintently. My first thought was intermod, but the various programs don't turn up a match for the receiver's frequency. A week ago we were able to visit the site and tightened several loose connectors on the other hardware in the site. Since then the interference does seem to be less but is still present on occasion. Observations of the site revealed that the public safety and the club's repeater antennas (DB-224 style, unsure of exact models) both share the top of the tower and are broadside to each other and are maybe four feet apart at most. So now our thinking is that the problem may be receiver overload. We set up a spare Celwave bandpass cavity that has about 2 dB of insertion loss and offers about 45 dB of insertion loss at the public safety's transmitter frequency. My question is whether the coax length is critical between the RX port of the Wacom duplexer and the input port of the Celwave cavity? I plan to send along a length of RG-393 (double shielded teflon coax) with the cavity. As far as I know, it is a random length. Should I cut it to something closer to 1/2 wavelength? 3/4 WL? Thanks! 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org
Re: [Repeater-Builder] Coax length between added cavity and duplexer
Yes, indeed it is a critical length if if is your desire to superimpose the bandpass curve properly on the pass curve of the duplexer. It should be an electrical 1/4 wave that accounts for the velocity propagation of the cable plus the electrical length of the coupling element in the Celwave cavity. If your end user doesn't have a tracking generator, IMO, attempting this is an exercise in futility. If all the bottles were built by the same OEM you could probably get a figure from their tech support group but with different OEMs you are going to have to cut/add and try. First tune the duplexer for the desired pass and reject frequencies. Then tune the pass cavity for the desired pass frequency. Then glue it all together with an interconnect that guestimates a 1/4 wave including the coupling length in the pass cavity and look at on the tracking generator to see whether the pass curve gets steeper but remains essentially the same. It most likely will not. Add a couple of right angle adaptors to the interconnect and see if the pass curve distortion gets better or worse. If it's worse, shorten the interconnect cable and try again. If it gets better, lengthen the interconnect. Having said that, I think Skipp's point is well taken - if the junk is on channel, an additional pass cavity isn't going to eliminate it. BTW, are you using an isolator on the TX? K7IJ In a message dated 7/26/2007 5:11:16 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: My question is whether the coax length is critical between the RX port of the Wacom duplexer and the input port of the Celwave cavity? I plan to send along a length of RG-393 (double shielded teflon coax) with the cavity. As far as I know, it is a random length. Should I cut it to something closer to 1/2 wavelength? 3/4 WL? ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour
