Re: [Repeater-Builder] Re: Coax shielding
At 08:40 AM 06/28/10, you wrote: Ian Wells kerin...@... wrote: Currently I have no filters between the link transmitter and its antenna. The next question in our Top Twenty Radio Hits - Countdown List is do you have any spare or available cavities to try a few things we might suggest? Selection B Are any extra or available to test with Cavities configured as band-pass, notch or some combination there of? s. Selection C Would you know the next winning 6 numbers for the Wednesday Evening California Supper Lotto? forget Selection C One of my friends supports a number of client sites. Once a week or so he has to call a tech support line to get an answer - anyone from Dell to HP to a software vendor. Once the system is back up he occasionally plays with the people on the telephone tech support lines... some companies script require the tech support person close with the line Is there anything else I can help you with? He always says Yes, in fact, six winning numbers. Most of the time that line gets a good laugh, followed by anything from Sorry, me first, on down. Only once in the last six months has he had a Huh?
[Repeater-Builder] Re: Coax shielding
Ian Wells kerin...@... wrote: Currently I have no filters between the link transmitter and its antenna. The next question in our Top Twenty Radio Hits - Countdown List is do you have any spare or available cavities to try a few things we might suggest? Selection B Are any extra or available to test with Cavities configured as band-pass, notch or some combination there of? s. Selection C Would you know the next winning 6 numbers for the Wednesday Evening California Supper Lotto? forget Selection C
Re: [Repeater-Builder] Re: Coax shielding
I have a bandpass/band notch diplexer that I am currently tuning up to replace the 6ld450s so we will see how it goes shortly . Thank You, Ian Wells, Kerinvale Comaudio, 3A Murchison Street,Biloela.4715 Ph 0749922449 or 0409159932 or 0749922574 www.kerinvalecomaudio.com.au ---Original Message--- From: skipp025 Date: 6/29/2010 1:44:33 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Coax shielding Ian Wells kerin...@... wrote: Currently I have no filters between the link transmitter and its antenna. The next question in our Top Twenty Radio Hits - Countdown List is do you have any spare or available cavities to try a few things we might suggest? Selection B Are any extra or available to test with Cavities configured as band-pass, notch or some combination there of? s. Selection C Would you know the next winning 6 numbers for the Wednesday Evening California Supper Lotto? forget Selection C
[Repeater-Builder] Re: Coax shielding
kerincom kerin...@... wrote: Hi guys .I am just wanted to confirm a question on coax shielding . Simple answer... It's there and never seems to behave exactly how you would expect it to. With 2-10 watts transmitting through rg213u could RF be escaping that could cause desensitization to other radios. RF can escape through some types of hard line (believe it or not). There always will be local area RF around, just a question of how much is coming through/from the coax braid and what if any grief it may be causing. If you're working at the 2 to 10 watt (what many of us assume is a fairly low) power level and you've got desense gremlins, smart money says you probably (also) have other or additional issues to deal with. The repeater I have setup uses 9 meters of heliax from the main diplexer to ant and rg213u from the link radio to its antenna. Nothing wrong with RG-213u especially when compared to other possible choices like someone using RG-58au. Just a question of loss per length and your preference with the end result values when you use/install it. I am finding I am getting problems with the link transmission interfering with the repeater rx. The link antenna is a yagi 3 meters above the ground and the main repeater antenna is 6 meters above it. So do some testing... put a termination (dummy load) on the end of the feed-line (regardless of the type you're using) at the Link-Yagi end. See if the problem goes away when you've got the Link Radio (transmitter) working at full power into the test termination (load). I am currently trying band pass cavity on the receiver rx or band pass/band reject diplexer with some success but I am wondering if the rf escaping from the cable is causing problems inside the repeater shed even at a low wattage. The proper type and placement of cavities will help, but you should first consider the Link Tx Termination Test I mention above. You don't yet know where the problem really originates from and you don't mention what type of repeater receiver you're using. Should we assume it's something of decent quality and that you have it properly protected. And what's the repeater transmitter doing when the link is active? Do you make the classic mistake of tie-wrapping the feed lines into one big bunch? I am definitely changing the rg213u to either rg223u or lmr400 as it is only on the link radio and shouldn't have any effect on the repeater's operation. Please... If you feel you must change the feed line, don't use any LMR type of coaxial line or you'll be wasting your and our time with additional problems. LMR-400 is not good coax to use in and around duplex (repeater) radio or any high adjacent RF environments. Has anyone else had the same sort of problem where the rf energy leaks out of the cable in the shed and causes problems to the repeater and they had to upgrade the link cable to 100% coverage cable You're not yet sure that's the problem and I'll bet the coax shielding value is not the large problem contribution you think it is. We'd need to know more about the radios, antennas, power levels, receiver and transmitter filtering (what we call Duplexer) or pre-selectors and notch cavities you might have around. Even though you're running RG-213u, it's not the best but when applied in modest length runs it's not the train wreck you might think it is. And you're on the bottom side of the earth in Auzzie Land so we have to flip the computer screen upside down to read your posts, but that's relatively easy. :-) Thank You, Ian Wells, your turn, s.
Re: [Repeater-Builder] Re: Coax shielding
Hi skip .The repeater radios are maxon sm4450sc and the link is a tait t2010 The test I have tried in the past have been definitely point to the link being the problem as when we turn the link off the repeater works to its full range but with it on we get desence. We used to have the link closer to the repeaters aprox 487mhz but we shifted it to 517mhz to fix desense and we find we are still having problems.I think the white noise could be the issue but I tried a notch on the link cable tuned to the repeaters receive and that seem to cause more interference and weaken the links Transmit range.I wondered about putting a BP cavity filter inline with the link but since our link frequencies are 5.2mhz apart I feel you can only tuned the filter for either TX or rx frequencies and not both Unless maybe you can install two in pararell ,one tuned to TX and the other rx . Thank You, Ian Wells, Kerinvale Comaudio, 3A Murchison Street,Biloela.4715 Ph 0749922449 or 0409159932 or 0749922574 www.kerinvalecomaudio.com.au ---Original Message--- From: skipp025 Date: 6/28/2010 2:50:00 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Coax shielding kerincom kerin...@... wrote: Hi guys .I am just wanted to confirm a question on coax shielding .
RE: [Repeater-Builder] Re: Coax shielding
Hi Ian, I think I'd be taking a close look at both transmitters with a spectrum analyser and seeing if they are both suitable for repeater work. I'm not familiar with either radio, but usually radios designed for duplex work go to a lot more trouble with internal shielding than your average mobile set. The other issue to consider is the impedance matching between all the components in the system. If the SWR is bad somewhere then there will be RF voltage on the outside of the coax linking mis-matched devices, regardless of how good the coax is. For instance if the link transmitter is seeing a high SWR into it's bandpass cavity then the jumper cable could be radiating unfiltered noise straight into the repeater receiver cable. It could also be that putting the bandpass filter in line has upset the SWR seen by the Link Tx and now radiates MORE noise in the shack. I've also seen some cavities make PA stages become unstable, creating very broad band noise, requiring both the cavities and PA to be retuned to solve the problem. 73,Mark VK3BYY From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kerincom Sent: Monday, 28 June 2010 08:19 AM To: mail=repeater-buil...@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Coax shielding Hi skip .The repeater radios are maxon sm4450sc and the link is a tait t2010.The test I have tried in the past have been definitely point to the link being the problem as when we turn the link off the repeater works to its full range but with it on we get desence. We used to have the link closer to the repeaters aprox 487mhz but we shifted it to 517mhz to fix desense and we find we are still having problems.I think the white noise could be the issue but I tried a notch on the link cable tuned to the repeaters receive and that seem to cause more interference and weaken the links Transmit range.I wondered about putting a BP cavity filter inline with the link but since our link frequencies are 5.2mhz apart I feel you can only tuned the filter for either TX or rx frequencies and not both Unless maybe you can install two in pararell ,one tuned to TX and the other rx . Thank You, Ian Wells, Kerinvale Comaudio, 3A Murchison Street,Biloela.4715 Ph 0749922449 or 0409159932 or 0749922574 www.kerinvalecomaudio.com.auhttp://www.kerinvalecomaudio.com.au/
RE: [Repeater-Builder] Re: Coax shielding
Currently I have no filters between the link transmitter and its antenna. Thank You ,Ian Wells Kerinvale Comaudio, 3A Murchison Street, Biloela.4715 Ph 0749922449 Mb 0409159932 Hm 0749922574 Fx 0749922767 www.kerinvalecomaudio.com.au ---Original Message--- From: Mark HARRISON Date: 06/28/10 11:10:52 To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Coax shielding Hi Ian, I think I'd be taking a close look at both transmitters with a spectrum analyser and seeing if they are both suitable for repeater work. I'm not familiar with either radio, but usually radios designed for duplex work go to a lot more trouble with internal shielding than your average mobile set. The other issue to consider is the impedance matching between all the components in the system. If the SWR is bad somewhere then there will be RF voltage on the outside of the coax linking mis-matched devices, regardless of how good the coax is. For instance if the link transmitter is seeing a high SWR into it's bandpass cavity then the jumper cable could be radiating unfiltered noise straight into the repeater receiver cable. It could also be that putting the bandpass filter in line has upset the SWR seen by the Link Tx and now radiates MORE noise in the shack. I've also seen some cavities make PA stages become unstable, creating very broad band noise, requiring both the cavities and PA to be retuned to solve the problem 73,Mark VK3BYY From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups com] On Behalf Of kerincom Sent: Monday, 28 June 2010 08:19 AM To: mail=repeater-buil...@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Coax shielding Hi skip .The repeater radios are maxon sm4450sc and the link is a tait t2010 The test I have tried in the past have been definitely point to the link being the problem as when we turn the link off the repeater works to its full range but with it on we get desence. We used to have the link closer to the repeaters aprox 487mhz but we shifted it to 517mhz to fix desense and we find we are still having problems.I think the white noise could be the issue but I tried a notch on the link cable tuned to the repeaters receive and that seem to cause more interference and weaken the links Transmit range.I wondered about putting a BP cavity filter inline with the link but since our link frequencies are 5.2mhz apart I feel you can only tuned the filter for either TX or rx frequencies and not both Unless maybe you can install two in pararell ,one tuned to TX and the other rx . Thank You, Ian Wells, Kerinvale Comaudio, 3A Murchison Street,Biloela.4715 Ph 0749922449 or 0409159932 or 0749922574 www.kerinvalecomaudio.com.au faint_grain.jpg
