[Repeater-Builder] Re: Linking and interference problem
John, Thanks for the more in-depth explanation. Link antenna and feedline is about as good as you can get. About the only improvement you might make is to get the two UHF antennas directly under each other. That creates a cone of silence and make for the best null. No need for the 7/8 other than a small improvement in signal loss. I would think about replacing all of the jumpers with silver plated double shielded coax. The filter that comes to mind for your link receiver would be a very precise crystal filter made for your link radio receive frequency. They are kinda pricey, so they may be out of your price range, but they are only a few KC wide. Since it sounds like the hub repeater is on a stable frequency and will most likely be there for a long time, the crystal filter makes sense. They are not re-tunable in the field since they are made for a very specific receive frequency. They have a little loss in them, but since you can run the squelch fully tight, you have enough headroom, and that should not be a problem. Other item I would recommend is to install a isolator on the UHF repeater transmitter before it gets to the duplexer. I am not sure what you are using for a duplexer, but I also might suggest locating a Telewave or similar 9 diameter to 12 diameter bandpass filter (one that has two connectors) to go between the UHF repeater transmitter and the duplexer. They use these large diameter UHF cavities for transmit combiners, but I have seen them on Ebay for reasonable prices from time to time. The larger diameter the cavity, the steeper the skirts on each side of the transmit frequency will be. I know this may sound backwards, but I would attack adding the isolator and additional filtering on the UHF transmitter as the first step. Once you have made the UHF repeater transmitter as clean as it can be, then you can move on to adding any additional filtering to the link receiver, if it is still needed. Joe - WA7JAW Joe, Thanks for asking.. Question #1 link antenna is on top. 8 element yagi vertical pointed 210 SW Question #2 No. They are on different legs and each is on the other side of the tower, almost directly opposite each other. Question #3 No preamp. Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units 150FT on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on the Yagi's. N type connectors. Wish we could afford 7/8, but we take what the club can afford and work with that. Our club has appox 50 members, sometimes more or less depending on when they pay there dues. Hi HI. I know you didn't ask, but just in case you needed to know, 7/8 is not an option for us right now. Agreed that even just a few extra db rejection would do the trick. It wouldn't take a lot I don't think based on the squelch test, but a few db I would be highly thankful for, and I just don't have the knowledge to know how to get there from here. (-: 73 de John Godfrey KE5NZY BARC Pres.
RE: [Repeater-Builder] Re: Linking and interference problem
Thanks so much Joe. I think your recommendation on filtering the output of the UHF repeater seems to make good since to me. We will start there. The duplexer is one of the smaller units as compared to the larger cans I have seen for UHF. I guess it is different designs. I know I have seen some UHF duplexers at Hamfest that where much smaller than our two meter stuff of course, but still much larger than the unit we are using. I don't know the difference, I assumed just different design technology, and not necessarily bigger is better. If I am wrong on that part, please let me know, because I have access to a UHF duplexer, the 4 can type (probably 4X8 or 10 tall, for a fairly small investment. I will first look into the exact filter you suggested. It makes since to me it is better to clean up the signal transmitted as much as possible anyway. Then we will follow your suggestions on the link radio receiver next as you have suggested if the problem persist. Thanks a billion to you and the group for all the help. 73 de John Godfrey KE5NZY BARC Pres. -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Burkleo Sent: Sunday, May 03, 2009 1:42 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Linking and interference problem John, Thanks for the more in-depth explanation. Link antenna and feedline is about as good as you can get. About the only improvement you might make is to get the two UHF antennas directly under each other. That creates a cone of silence and make for the best null. No need for the 7/8 other than a small improvement in signal loss. I would think about replacing all of the jumpers with silver plated double shielded coax. The filter that comes to mind for your link receiver would be a very precise crystal filter made for your link radio receive frequency. They are kinda pricey, so they may be out of your price range, but they are only a few KC wide. Since it sounds like the hub repeater is on a stable frequency and will most likely be there for a long time, the crystal filter makes sense. They are not re-tunable in the field since they are made for a very specific receive frequency. They have a little loss in them, but since you can run the squelch fully tight, you have enough headroom, and that should not be a problem. Other item I would recommend is to install a isolator on the UHF repeater transmitter before it gets to the duplexer. I am not sure what you are using for a duplexer, but I also might suggest locating a Telewave or similar 9 diameter to 12 diameter bandpass filter (one that has two connectors) to go between the UHF repeater transmitter and the duplexer. They use these large diameter UHF cavities for transmit combiners, but I have seen them on Ebay for reasonable prices from time to time. The larger diameter the cavity, the steeper the skirts on each side of the transmit frequency will be. I know this may sound backwards, but I would attack adding the isolator and additional filtering on the UHF transmitter as the first step. Once you have made the UHF repeater transmitter as clean as it can be, then you can move on to adding any additional filtering to the link receiver, if it is still needed. Joe - WA7JAW Joe, Thanks for asking.. Question #1 link antenna is on top. 8 element yagi vertical pointed 210 SW Question #2 No. They are on different legs and each is on the other side of the tower, almost directly opposite each other. Question #3 No preamp. Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units 150FT on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on the Yagi's. N type connectors. Wish we could afford 7/8, but we take what the club can afford and work with that. Our club has appox 50 members, sometimes more or less depending on when they pay there dues. Hi HI. I know you didn't ask, but just in case you needed to know, 7/8 is not an option for us right now. Agreed that even just a few extra db rejection would do the trick. It wouldn't take a lot I don't think based on the squelch test, but a few db I would be highly thankful for, and I just don't have the knowledge to know how to get there from here. (-: 73 de John Godfrey KE5NZY BARC Pres.
RE: [Repeater-Builder] Re: Linking and interference problem
Joe, the UHF link radio which is the only one receiving the interference, is a GE Master II mobile. The rest are GE Master II stuff as well, but they are what I guess you are calling the station configuration, because we have them rack mounted and the door opens up like a hinge and the components and boards accessible that way. I am just the helper on this project as you can tell, and my knowledge is very weak on this issue. At the moment the problem has been minimized to a large degree based on setting the squelch as tight as it will go, and the receive signal still breaks the squelch and the interference can't. However when the receive signal drops, you can still hear the sound for like 50ms on the squelch tale. The person who does our repeater work KD5HPK could answer any questions about the equipment much better than I could, but his request to me was to try to find a narrow notch filter for the frequencies as per the original email. I added the dialog in the original email, so you guys could help me determine the best approach. I know it seemed like a lot of rambling. I have no way to know what all is on the site as it has maybe 15 antennas on the tower that I don't even know who they belong to. It is a commercial tower site with many systems and even different buildings that we don't have access to. We have identified however that we only get the feedback when both our UHF units are active and no other time. We also can link either on into the 2 meter repeater with no problems. We have duplexers on both repeaters of course and not the link radio as it isn't full duplex. The reason we are tied to those frequencies is that we are linked to several other repeaters and in one direction the UHF Main hub is 75 miles away and they can't change there frequencies because several are linked into it. In the other direction folks link into our UHF repeater from 50 miles away and that freq is set due to the fact that those guys have all their equipment configured for that frequency. So to make the long story short we are the link in the middle. Repeater pairs in our location are not easily changed due to what I have mentioned, plus there are not a lot of them left to coordinate anyhow. If we can just keep the transmit of the UHF repeater out of the input on the link radio.. problem solved. We have proven that with the squelch method, and while that will work for now. We don't like the little dirty squelch tale as it doesn't sound perfect, and don't we all strive for perfection (-: I think the right kind of filter would make it perfect, but I am not sure of that,,, where to find one,, what to call it,, or how to build it.. That to me seems to be the question.. If I am asking the wrong question.. Please just overlook my lack of knowledge on the subject. I build a great amplifier, repeaters are just not my strong suit yet, but I am starting to learn it. 73 de John Godfrey -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Burkleo Sent: Saturday, May 02, 2009 12:07 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Linking and interference problem john, Forgot to ask in my first reply. I am assuming that your link radio is also a Mastr II from your original post. Is it a mobile or a station configuration? Thanks, Joe --- In Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com, John Godfrey ke5...@... wrote: I was hoping you can help our club with a repeater link problem. What we have are all GE master 2 stuff. Here is what we have going on. we have had for years a 147.270 + repeater that works great. Last year we added a link into a central state repeater system using a link radio on one of our ports. It transmits on 442.025 and receives on 443.2. For six months we have used the link fine without problems. Last week we installed on another port a uhf repeater to be used as a hub for the north central part of our state to also link to us and the central state system. The UHF Repeater receives on 449.750 and transmits on 444.750. We can link the 270 to either the link to central state or the UHF repeater hub with no problems, but when we link the 270 to both or just link the UHF repeater to the link radio, once the UHF repeater is keyed up, the input on the link radio is hearing it so we have an awful squeal and intermod back into the 270. There is also a pager at the location that I can hear when this happens but not any other time. Again they work fine as long as both UHF machines are not in use at the same time. When the 270 is linked into Central state, even if the UHF repeater is not linked in, if you key the UHF repeater you here the squeal on the 270. I can see how as the link input goes out over the 270 when they are linked. I am not sure why I can also here it on the UHF repeater when I unkey it, even if it isn't linked in. Other than
RE: [Repeater-Builder] Re: Linking and interference problem
Joe, Thanks for asking.. Question #1 link antenna is on top. 8 element yagi vertical pointed 210 SW Question #2 No. They are on different legs and each is on the other side of the tower, almost directly opposite each other. Question #3 No preamp. Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units 150FT on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on the Yagi's. N type connectors. Wish we could afford 7/8, but we take what the club can afford and work with that. Our club has appox 50 members, sometimes more or less depending on when they pay there dues. Hi HI. I know you didn't ask, but just in case you needed to know, 7/8 is not an option for us right now. Agreed that even just a few extra db rejection would do the trick. It wouldn't take a lot I don't think based on the squelch test, but a few db I would be highly thankful for, and I just don't have the knowledge to know how to get there from here. (-: 73 de John Godfrey KE5NZY BARC Pres. -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Burkleo Sent: Saturday, May 02, 2009 12:04 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Linking and interference problem John, I like the others on here believe that your frequency and antenna spacing is too close to work with out filters and/or additional isolation. I do have a couple questions about your UHF antennas and their placement on the tower. 1. What type of antenna are you using for your link and is it the top or bottom antenna? 2. Are both UHF antennas on the same tower leg and spaced out the same distance so they are pretty much directly underneath or above each other? 3. Do you have a preamp on the link receiver, if so what brand? 4. What are you using for feedline and cables inside the building for the UHF repeater and link radio? I am trying to come up with some other ideas that will buy you a few extra DB of rejection here and there. A little here and there and pretty soon you have another 10-20 db of isolation you did not have before. Joe - WA7JAW --- In Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com, John Godfrey ke5...@... wrote: I was hoping you can help our club with a repeater link problem. What we have are all GE master 2 stuff. Here is what we have going on. we have had for years a 147.270 + repeater that works great. Last year we added a link into a central state repeater system using a link radio on one of our ports. It transmits on 442.025 and receives on 443.2. For six months we have used the link fine without problems. Last week we installed on another port a uhf repeater to be used as a hub for the north central part of our state to also link to us and the central state system. The UHF Repeater receives on 449.750 and transmits on 444.750. We can link the 270 to either the link to central state or the UHF repeater hub with no problems, but when we link the 270 to both or just link the UHF repeater to the link radio, once the UHF repeater is keyed up, the input on the link radio is hearing it so we have an awful squeal and intermod back into the 270. There is also a pager at the location that I can hear when this happens but not any other time. Again they work fine as long as both UHF machines are not in use at the same time. When the 270 is linked into Central state, even if the UHF repeater is not linked in, if you key the UHF repeater you here the squeal on the 270. I can see how as the link input goes out over the 270 when they are linked. I am not sure why I can also here it on the UHF repeater when I unkey it, even if it isn't linked in. Other than the last part of that it would make since to ne that I have the two 440 antennas to close. We have them about 10 feet apart, but the one can't go higher and the other can't go lower and still serve the purpose needed. I am thinking I need some kind of filter, that I can put on the link radio, that will protect it from the transmit of the UHF repeater. In other words the 444.750 is coming in my receive on the 443.2. Changing freq is not an option due to several reasons. If I had a filter of some sort, that would either allow say 442-443.5 to pass and attenuate everything else that would be great. Or something that would pass 442-443.5 and attenuate everything above 443.5, then that would work. Guys, what am I looking for and where might I find it. Must I build something that is this custom, or can I buy it. If I must build it, where should I start. If I can buy it,, where from and what would they call it. If my thoughts are off base, please help me to know what other questions I need to answer to solve such a problem as this. I thought maybe the pager was just interfering, but why would the 270 work fine when linked to the link radio, or linked to the UHF repeater, and the only time we have the problem
Re: [Repeater-Builder] Re: Linking and interference problem
MessageIf you can hear another service in there at the time, you likely have an intermod issue. Do yourself a favor and get rid of the foil/braid jumpers. They could be where the mix is happening. If not, you've ruled that out. Somewhere there is a mix and you have to play detective until it is found. Chuck WB2EDV - Original Message - From: John Godfrey To: Repeater-Builder@yahoogroups.com Sent: Saturday, May 02, 2009 2:59 AM Subject: RE: [Repeater-Builder] Re: Linking and interference problem Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units 150FT on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on the Yagi's. N type connectors.
[Repeater-Builder] Re: Linking and interference problem
I just made a very quick read of your description of the problem. I agree that you very likely are experiencing desense because of the meg and a half difference between one of your UHF TX and one Rx. This is a pretty common problem when more than one system is located at a site. A quick look at a generic Tx / Rx isolation graph shows at a meg and a half you need about 85 dB of isolation at UHF. (assuming something like 25 watts) Your antenna spacing (sounds like about 4 wavelengths) might be giving you 22 dB or so. You are probably going to need to build a window filter which is similar to a duplexer. You might be able to use just a couple of cavities and notch the unwanted Tx from your Rx if the cavities you use can notch that close. You can also get some notching by using critical length cables to maximize whatever notch pass response the cavities already give. You likely will need the help of someone in your area with a tracking generator to help. And with physically close spaced transmitters like you have, I would be a good idea to get transmitter isolators to avoid problems in the future. Keep in mind the numbers above are a quick rough estimate. However you really are looking at something around 60 dB of additional isolation no matter what calculation you use.
[Repeater-Builder] Re: Linking and interference problem
John, I like the others on here believe that your frequency and antenna spacing is too close to work with out filters and/or additional isolation. I do have a couple questions about your UHF antennas and their placement on the tower. 1. What type of antenna are you using for your link and is it the top or bottom antenna? 2. Are both UHF antennas on the same tower leg and spaced out the same distance so they are pretty much directly underneath or above each other? 3. Do you have a preamp on the link receiver, if so what brand? 4. What are you using for feedline and cables inside the building for the UHF repeater and link radio? I am trying to come up with some other ideas that will buy you a few extra DB of rejection here and there. A little here and there and pretty soon you have another 10-20 db of isolation you did not have before. Joe - WA7JAW --- In Repeater-Builder@yahoogroups.com, John Godfrey ke5...@... wrote: I was hoping you can help our club with a repeater link problem. What we have are all GE master 2 stuff. Here is what we have going on. we have had for years a 147.270 + repeater that works great. Last year we added a link into a central state repeater system using a link radio on one of our ports. It transmits on 442.025 and receives on 443.2. For six months we have used the link fine without problems. Last week we installed on another port a uhf repeater to be used as a hub for the north central part of our state to also link to us and the central state system. The UHF Repeater receives on 449.750 and transmits on 444.750. We can link the 270 to either the link to central state or the UHF repeater hub with no problems, but when we link the 270 to both or just link the UHF repeater to the link radio, once the UHF repeater is keyed up, the input on the link radio is hearing it so we have an awful squeal and intermod back into the 270. There is also a pager at the location that I can hear when this happens but not any other time. Again they work fine as long as both UHF machines are not in use at the same time. When the 270 is linked into Central state, even if the UHF repeater is not linked in, if you key the UHF repeater you here the squeal on the 270. I can see how as the link input goes out over the 270 when they are linked. I am not sure why I can also here it on the UHF repeater when I unkey it, even if it isn't linked in. Other than the last part of that it would make since to ne that I have the two 440 antennas to close. We have them about 10 feet apart, but the one can't go higher and the other can't go lower and still serve the purpose needed. I am thinking I need some kind of filter, that I can put on the link radio, that will protect it from the transmit of the UHF repeater. In other words the 444.750 is coming in my receive on the 443.2. Changing freq is not an option due to several reasons. If I had a filter of some sort, that would either allow say 442-443.5 to pass and attenuate everything else that would be great. Or something that would pass 442-443.5 and attenuate everything above 443.5, then that would work. Guys, what am I looking for and where might I find it. Must I build something that is this custom, or can I buy it. If I must build it, where should I start. If I can buy it,, where from and what would they call it. If my thoughts are off base, please help me to know what other questions I need to answer to solve such a problem as this. I thought maybe the pager was just interfering, but why would the 270 work fine when linked to the link radio, or linked to the UHF repeater, and the only time we have the problem is when the 270 is linked to the link radio and the UHF repeater is keyed up, regardless of whether the UHF repeater is linked in or not. I know my question is long, but m hope was to explain the problem with enough detail that you might have an answer for me. Your help would be greatly appreciated by our Club. 73 de John Godfrey KE5NZY BARC Pres. DISTRICT B ADEC ASTEN NM
[Repeater-Builder] Re: Linking and interference problem
john, Forgot to ask in my first reply. I am assuming that your link radio is also a Mastr II from your original post. Is it a mobile or a station configuration? Thanks, Joe --- In Repeater-Builder@yahoogroups.com, John Godfrey ke5...@... wrote: I was hoping you can help our club with a repeater link problem. What we have are all GE master 2 stuff. Here is what we have going on. we have had for years a 147.270 + repeater that works great. Last year we added a link into a central state repeater system using a link radio on one of our ports. It transmits on 442.025 and receives on 443.2. For six months we have used the link fine without problems. Last week we installed on another port a uhf repeater to be used as a hub for the north central part of our state to also link to us and the central state system. The UHF Repeater receives on 449.750 and transmits on 444.750. We can link the 270 to either the link to central state or the UHF repeater hub with no problems, but when we link the 270 to both or just link the UHF repeater to the link radio, once the UHF repeater is keyed up, the input on the link radio is hearing it so we have an awful squeal and intermod back into the 270. There is also a pager at the location that I can hear when this happens but not any other time. Again they work fine as long as both UHF machines are not in use at the same time. When the 270 is linked into Central state, even if the UHF repeater is not linked in, if you key the UHF repeater you here the squeal on the 270. I can see how as the link input goes out over the 270 when they are linked. I am not sure why I can also here it on the UHF repeater when I unkey it, even if it isn't linked in. Other than the last part of that it would make since to ne that I have the two 440 antennas to close. We have them about 10 feet apart, but the one can't go higher and the other can't go lower and still serve the purpose needed. I am thinking I need some kind of filter, that I can put on the link radio, that will protect it from the transmit of the UHF repeater. In other words the 444.750 is coming in my receive on the 443.2. Changing freq is not an option due to several reasons. If I had a filter of some sort, that would either allow say 442-443.5 to pass and attenuate everything else that would be great. Or something that would pass 442-443.5 and attenuate everything above 443.5, then that would work. Guys, what am I looking for and where might I find it. Must I build something that is this custom, or can I buy it. If I must build it, where should I start. If I can buy it,, where from and what would they call it. If my thoughts are off base, please help me to know what other questions I need to answer to solve such a problem as this. I thought maybe the pager was just interfering, but why would the 270 work fine when linked to the link radio, or linked to the UHF repeater, and the only time we have the problem is when the 270 is linked to the link radio and the UHF repeater is keyed up, regardless of whether the UHF repeater is linked in or not. I know my question is long, but m hope was to explain the problem with enough detail that you might have an answer for me. Your help would be greatly appreciated by our Club. 73 de John Godfrey KE5NZY BARC Pres. DISTRICT B ADEC ASTEN NM
