While your logic is good on this, a Pass/Reject would help THAT transmitter be more friendly to other receivers... and protect from raw RF overload from other near-but-not-on-frequency transmitters... but the noise geration issue ( part 2 of my general site comments) needs to be plugged up on the tx that is causing it....so filters need to be on the link TX itself... especially if you want to keep the link frequency agile.. the proposed notch filters would allow the link to be moved if you needed, as long as you stay at least 1 mhz away from the notched 478 frequency... Now.. if there are ever more receivers on site, those cases will need to be addressed with better filtering or antenna spacing :-) Doug
kerincom wrote: > > > That's what I thought as I am currently using a 6ld450s notch diplexer > and should change it to a band pass/band reject diplexer .I tried a > experiment on site where I added 1 cavity inline with the receiver > 478.675 and it seemed to improve the problem .so that was going to be > the next step but I thought I might see what the thoughts were on the > coax leaking > > > > > > 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/> > > /-------Original Message-------/ > > /*From:*/ Doug Bade <mailto:[email protected]> > /*Date:*/ 6/28/2010 1:44:27 AM > /*To:*/ [email protected] > <mailto:[email protected]> > /*Subject:*/ Re: [Repeater-Builder] Coax shielding > > > > Ian; > It would seem that at uhf ~30mhz away cable leakage in the shed > would seem to be less likely than antenna to antenna interference. In > general it is the white noise generated by a transmitter on other > frequencies that is most likely to cause desense to a co located rx. > > Assuming you have double shielded or better on the repeater, the leakage > in the shed from the single shielded link radio would not seem to > radiate enough to be an issue. If the radio side of the main duplexer is > also rg213, well that is another matter :-) > If you are using a notch only duplexer for the main duplexer, it would > not protect you from another transmitter besides it's own.. Typical > mobile type size duplexers at UHF are really only designed to protect > the rx from it's local tx, any other can slip right in.. > > I would try a notch filter ( or half a notch duplexer ) on the link tx > to suppress the station rx frequency from it's output.. that noise is > probably the culprit.. > > As said by others, good double shielded cables and /or 100 % corrugated > types are suggested in sites with multiple transmitters to deal with.. > but most on site desense I have dealt with from other transmitters comes > from one of 2 things.. raw power front end overload of the rx when the > antennas can see each other... or white noise generated on broad > frequencies from an unfiltered transmitter. I am suggesting a notch > cavity on the 517 transmitter output that notches 478.675 in this case.. > 3 slugs ( one side) on a mobile duplexer will suppress that noise ~65db, > and provide no significant insertion loss to the link tx..And double > shielded cables like RG142 for radio to filter connections is perfectly > adequate up to 520 mhz and beyond... with isolation to -120dbm at a > minimum.. > > Doug > KD8B > > kerincom wrote: > > > > > > Uhf the link is 517mhz and the repeater TX/rx pair is 473.475 and > > 478.675mhz on one repeater and it is in a weak area with the main > > site so it has to transmitt aprox 10 watts > > > > > > > > > > kerincom wrote: > > > > > > > > > Hi guys .I am just wanted to confirm a question on coax shielding . > > > With 2-10 watts transmitting through rg213u could rf be escaping that > > > could cause desensitization to other radios .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 . > > > 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 .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 .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 > > > .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 > > > > > > > > > > > > > > > > > >
