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<http://www.kerinvalecomaudio.com.au/>
