[Repeater-Builder] UHF duplexers and preamps
Hi all, We are currently applying for a 7.6Mhz split UHF repeater here which means we will be able to do away with the old and lossy large cavity filters for our old 1.6Mhz split repeater and use a commercial unit. We've already tried a loaned Procom duplexer and the results are most promising with no TX desense or noise noted on the RX and minimal loss of TX power. As we now need to purchase a filter for ourselves I've come across these on Ebay, has anyone any experience of them? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185 Looking through the archives I can see some groups use pre amps on 70cm repeaters, this isn't something we've considered before but presuming they fit between the RX and the duplexer how effective are they? If they are worth considering what make and model is favourite? 73 Paul
Re: [Repeater-Builder] UHF duplexers and preamps
Hey there, you pay a little more for them, but the angle liniar preamps are awesome. They come with a filter. Like i said, you pay about twice the price of an ARR, but overall, it is a much much better pre amp. So many people just hook up a preamp. What good is it if you're getting all kinds of junk on your receiver at the same time. On Dec 26, 2007, at 4:34 AM, aceblaggard wrote: Hi all, We are currently applying for a 7.6Mhz split UHF repeater here which means we will be able to do away with the old and lossy large cavity filters for our old 1.6Mhz split repeater and use a commercial unit. We've already tried a loaned Procom duplexer and the results are most promising with no TX desense or noise noted on the RX and minimal loss of TX power. As we now need to purchase a filter for ourselves I've come across these on Ebay, has anyone any experience of them? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185 Looking through the archives I can see some groups use pre amps on 70cm repeaters, this isn't something we've considered before but presuming they fit between the RX and the duplexer how effective are they? If they are worth considering what make and model is favourite? 73 Paul
Re: [Repeater-Builder] UHF duplexers and preamps
Remeber, there is a big difference between the 4 cavity mobile duplexer and the 6 cavity set. I have obtained 95-100dB of notch with this type of duplexer with a 5 MHz split, but that was the 6 cavity type. The 4 cavity is not worth the powder to blow it to hell. The safe amount of power is 25 watts. Some specs will say 50 is the maximum depending on who made it. Ken is correct. You do not want to use this type of duplexer for a mountian top or a serious 2 way site. This is more meant for the buisness that has a repeater on a desk trying to cover their building and parking lot. The notches only cover the repeater input and output frequencies, adjacent channel and out of band signals go right in to the receiver with very little attenuation. The original design for the notch type of duplexer was for IMTS Mobile Telephone service. On 12/26/07, Ken Arck [EMAIL PROTECTED] wrote: At 01:34 AM 12/26/2007, you wrote: We are currently applying for a 7.6Mhz split UHF repeater here which means we will be able to do away with the old and lossy large cavity filters for our old 1.6Mhz split repeater and use a commercial unit. We've already tried a loaned Procom duplexer and the results are most promising with no TX desense or noise noted on the RX and minimal loss of TX power. As we now need to purchase a filter for ourselves I've come across these on Ebay, has anyone any experience of them? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185 Looking through the archives I can see some groups use pre amps on 70cm repeaters, this isn't something we've considered before but presuming they fit between the RX and the duplexer how effective are they? If they are worth considering what make and model is favourite? ---Hi Paul. First of all, the type of duplexer you're looking at is a notch only type. Secondly, I find their claim of 75 dB isolation and 1 dB insertion loss pretty comical. I'd go so far as to say that claim is total BS. Even at your spacing of 7.5 mHz, I don't see how the performance is anywhere near as good as they claim. You ca' not fight the law of physics as Scotty would say. A notch-only type duplexer is usually adequate for lower power repeaters in a low RF environment. I would certainly NEVER use one at a radio site where other radios/repeaters reside as they do not offer adequate out-of-band rejection nor even adequate in-band rejection. To further complicate things, adding a preamp would probably be a complete disaster without adding additional filtering. I do agree with Jed that AngleLinear makes most excellent preamps with just the right amount of gain for a repeater preamp, whereas ones such as ARR have WY too much gain. The purpose of a preamp in a repeater (assuming your receiver is worth a damn in the first place) is to overcome the loss of the duplexer and feedline. Too much gain opens the door to all sorts of issues, not the least of which are desense and front-end overloading. And again, using one with the typical mobile duplexer will probably cause problems anyway. You can find good deals on used band-pass/band-reject UHF duplexers, usually quite easily. My advice is to buy one of those and forget about the mobile type. Ken -- 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] UHF duplexers and preamps
At 01:34 AM 12/26/2007, you wrote: We are currently applying for a 7.6Mhz split UHF repeater here which means we will be able to do away with the old and lossy large cavity filters for our old 1.6Mhz split repeater and use a commercial unit. We've already tried a loaned Procom duplexer and the results are most promising with no TX desense or noise noted on the RX and minimal loss of TX power. As we now need to purchase a filter for ourselves I've come across these on Ebay, has anyone any experience of them? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185 Looking through the archives I can see some groups use pre amps on 70cm repeaters, this isn't something we've considered before but presuming they fit between the RX and the duplexer how effective are they? If they are worth considering what make and model is favourite? ---Hi Paul. First of all, the type of duplexer you're looking at is a notch only type. Secondly, I find their claim of 75 dB isolation and 1 dB insertion loss pretty comical. I'd go so far as to say that claim is total BS. Even at your spacing of 7.5 mHz, I don't see how the performance is anywhere near as good as they claim. You ca' not fight the law of physics as Scotty would say. A notch-only type duplexer is usually adequate for lower power repeaters in a low RF environment. I would certainly NEVER use one at a radio site where other radios/repeaters reside as they do not offer adequate out-of-band rejection nor even adequate in-band rejection. To further complicate things, adding a preamp would probably be a complete disaster without adding additional filtering. I do agree with Jed that AngleLinear makes most excellent preamps with just the right amount of gain for a repeater preamp, whereas ones such as ARR have WY too much gain. The purpose of a preamp in a repeater (assuming your receiver is worth a damn in the first place) is to overcome the loss of the duplexer and feedline. Too much gain opens the door to all sorts of issues, not the least of which are desense and front-end overloading. And again, using one with the typical mobile duplexer will probably cause problems anyway. You can find good deals on used band-pass/band-reject UHF duplexers, usually quite easily. My advice is to buy one of those and forget about the mobile type. Ken -- 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] UHF duplexers and preamps
At 12/26/2007 10:00, you wrote: Remeber, there is a big difference between the 4 cavity mobile duplexer and the 6 cavity set. I have obtained 95-100dB of notch with this type of duplexer with a 5 MHz split, but that was the 6 cavity type. The 4 cavity is not worth the powder to blow it to hell. ...unless you have some specialized filtering requirement that can make use of it. At one site I have a UHF downlink TX assignment only 1 MHz away from an uplink RX just under 2 MHz away from an input RX. The downlink TX is on a separate Yagi antenna pointed away from the main omni that the RXs are on but with only ~20 ft. of horizontal separation no vertical separation. To keep the downlink TX noise out of both of those RXs I use one side of a 4 section notch duplexer adjusted to yield about 35 dB of rejection at the two RX freqs. Normally this duplexer only provided ~55 dB of rejection, not good enough for single antenna use, but as a notch filter for this application it works fine. Bob NO6B
Re: [Repeater-Builder] UHF duplexers and preamps
I'm sorry, I meant to say when used as a duplexer, The 4 cavity model is not worth the powder to blow it to hell. I should also point out that the auction in question shows the sawed off model and not the full 1/4 wave length version. A proper mobile duplexer should have cavities 6 to 7 long. I am not sure what is that one, but I would suspect helical resonators. On 12/26/07, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: At 12/26/2007 10:00, you wrote: Remeber, there is a big difference between the 4 cavity mobile duplexer and the 6 cavity set. I have obtained 95-100dB of notch with this type of duplexer with a 5 MHz split, but that was the 6 cavity type. The 4 cavity is not worth the powder to blow it to hell. ...unless you have some specialized filtering requirement that can make use of it. At one site I have a UHF downlink TX assignment only 1 MHz away from an uplink RX just under 2 MHz away from an input RX. The downlink TX is on a separate Yagi antenna pointed away from the main omni that the RXs are on but with only ~20 ft. of horizontal separation no vertical separation. To keep the downlink TX noise out of both of those RXs I use one side of a 4 section notch duplexer adjusted to yield about 35 dB of rejection at the two RX freqs. Normally this duplexer only provided ~55 dB of rejection, not good enough for single antenna use, but as a notch filter for this application it works fine. Bob NO6B Yahoo! Groups Links
Re: [Repeater-Builder] UHF duplexers and preamps
On Dec 26, 2007, at 2:31 PM, DCFluX wrote: Here in Portland, Oregon we have group that has about 4-5 two meter repeaters all linked together. They seem to think they need that many repeaters just to cover the metro area. Their repeaters usually have TERRIBLE sounding audio and often have squelching problems. The main person who operates this system sits on the repeater coordination council and keeps scamming more repeater pairs for his group every couple years. Here is their link: http://www.worc.info/worc_system.htm For HT's they might. (Not saying they do, I don't know the situation... just saying -- 5W HT's to 50W repeaters (after the duplexer) isn't balanced, and never performs right.) Ever offered to help them fix the squelching problems? They're (apparently) not going away. You know the old adage, if you can't beat 'em, join 'em. It's not a competition anyway. Too much of that sentiment in repeater operation already anyway... Just out of technical curiosity, what's a squelching problem anyway? Are you saying the machines are receiving crud and continually open up on it, or are you saying you don't like the way the squelch action sounds? They're kinda two different levels of problem. One is serious, the other is mostly cosmetic. Often times, their repeaters sit idle. Talk on 'em. :-) Mean while, the waiting list keeps growing. It always will until people learn to work together. It's a great sociology thesis paper waiting to be written: Ham Radio: How people don't help each other but complain about each other's systems incessantly. (GRIN) I'm not picking on you personally, your note is just a great example of the problem at hand in MANY cities: It's a sociology paper because there will ALWAYS be the I can do it better crowd owning and operating repeaters. You don't like how their systems sound, so you get on a waiting list to show them you can do it better. How we break this cycle of disfunction, I don't know. How about fixing their machines? (I've made verbal offers to other clubs to merge our clubs, remove or re-task repeaters that offer similar coverage, and build links that can be connected/disconnected at-will. No one's interested. And Denver's got a lot of good technical folks and repeater builders. If the only interesting thing about building repeaters is to say you did yours the way you want to, this problem will never end. Sadly, I think the only thing that could ever cause a merger would be really hard times. Some club would have to be in such financial dire straits that they'd want to sell off their repeater assets to someone else.) Anyone reading along have any ideas on how to stop this madness? At every site my club has a machine at, there's at least four other Amateur systems -- not always on the same band, but often yes. I often ask myself, What's the point?... but our members don't interact with the other club's members, and vice-versa. It's nuts. -- Nate Duehr, WY0X [EMAIL PROTECTED]
Re: [Repeater-Builder] UHF duplexers and preamps
Hi Nate- You are correct, you don't know the situation. There are plenty of systems that provide good metro coverage with 1 or maybe 2 repeaters here in Portland. Simply put, these people don't play nice. They often make their gain by character assination, and have a lengthy record seen by several people. The squelching problem is repeater receivers blowing squelch noise for on a regular basis for months, I call that serious! The audio has often sounded poor to bad in the past, I call that cosmetic. I don't chose to talk on the repeaters. Once, about years ago I allowed my son to talk on their repeater using my callsign with me there as the control op. He was having a plesant conversation with someone there and the system was then shut down. The repeater owner statements made it clear he did not like a youngster using their repeater. That is hardly what I call good amateur practice. The last time I was in Denver, I had no problem finding inactive 2 meter repeaters to talk to NP4AI on. -- Original Message -- Received: Wed, 26 Dec 2007 05:57:58 PM CST From: Nate Duehr [EMAIL PROTECTED] For HT's they might. (Not saying they do, I don't know the situation... just saying -- 5W HT's to 50W repeaters (after the duplexer) isn't balanced, and never performs right.) Ever offered to help them fix the squelching problems? They're (apparently) not going away. You know the old adage, if you can't beat 'em, join 'em. It's not a competition anyway. Too much of that sentiment in repeater operation already anyway... Just out of technical curiosity, what's a squelching problem anyway? Are you saying the machines are receiving crud and continually open up on it, or are you saying you don't like the way the squelch action sounds? They're kinda two different levels of problem. One is serious, the other is mostly cosmetic. Often times, their repeaters sit idle. Talk on 'em. :-) Mean while, the waiting list keeps growing. It always will until people learn to work together. It's a great sociology thesis paper waiting to be written: Ham Radio: How people don't help each other but complain about each other's systems incessantly. (GRIN) I'm not picking on you personally, your note is just a great example of the problem at hand in MANY cities: It's a sociology paper because there will ALWAYS be the I can do it better crowd owning and operating repeaters. You don't like how their systems sound, so you get on a waiting list to show them you can do it better. How we break this cycle of disfunction, I don't know. How about fixing their machines? (I've made verbal offers to other clubs to merge our clubs, remove or re-task repeaters that offer similar coverage, and build links that can be connected/disconnected at-will. No one's interested. And Denver's got a lot of good technical folks and repeater builders. If the only interesting thing about building repeaters is to say you did yours the way you want to, this problem will never end. Sadly, I think the only thing that could ever cause a merger would be really hard times. Some club would have to be in such financial dire straits that they'd want to sell off their repeater assets to someone else.) Anyone reading along have any ideas on how to stop this madness? At every site my club has a machine at, there's at least four other Amateur systems -- not always on the same band, but often yes. I often ask myself, What's the point?... but our members don't interact with the other club's members, and vice-versa. It's nuts. -- Nate Duehr, WY0X [EMAIL PROTECTED]
Re: [Repeater-Builder] UHF duplexers and preamps
On Dec 26, 2007, at 5:39 PM, JOHN MACKEY wrote: Simply put, these people don't play nice. They often make their gain by character assination, and have a lengthy record seen by several people. Too bad we can't vote 'em off the island, eh? :-) The squelching problem is repeater receivers blowing squelch noise for on a regular basis for months, I call that serious! The audio has often sounded poor to bad in the past, I call that cosmetic. Yep. I don't chose to talk on the repeaters. Once, about years ago I allowed my son to talk on their repeater using my callsign with me there as the control op. He was having a plesant conversation with someone there and the system was then shut down. The repeater owner statements made it clear he did not like a youngster using their repeater. That is hardly what I call good amateur practice. Lovely people. The last time I was in Denver, I had no problem finding inactive 2 meter repeaters to talk to NP4AI on. LOL. You know Brad, eh? He's an interesting guy. He suffers from the design problem in the Icom 706... he forgets to turn his mic gain back down to something reasonable when switching from SSB to FM. Heh. Sounds awful until someone reminds him. I'm so glad the FT-857D designers paid attention and didn't design in the same problem in Yaesu's all-band/all-mode contender. (GRIN) As far as repeater activity -- it's okay but there's definitely nights when things are quiet around here. Other nights, various systems are all busy at the same time. The linked VHF repeaters in our club get used for Nets almost every night of the week, which is nice to hear... -- Nate Duehr, WY0X [EMAIL PROTECTED]
