The conversion was done per the repeater builders page on maxtrac conversions. I first used the standard 2 pole gigifilters you can for 900mhz later replaced with 3 pole filters. This improved the site degradation by about 5 db. I remove the PA and install a female N connector on the back of the maxtrac. I also pull the DC power connector from the PA and install it on the back of the Maxtrac. I have one maxtrac that I installed in a 19" rack extruded aluminum box with an N RF connector and all inputs\outputs going thru feed thru caps. This showed no improvement. I do not believe I am dealing with a signal on the input frequency but with a very high level of RF energy at the receiver input that it is affecting the sensitivity of the Receiver.
David N9CZV _____ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Thursday, November 22, 2007 12:59 PM To: Repeater-Builder@yahoogroups.com Subject: RE: RE: [Repeater-Builder] Receiver overload David, This is definitely an interesting thread! I cannot think of a more suitable topic to discuss in this forum. You mentioned in your original post that you are using a converted 800 MHz MaxTrac mobile radio as your 900 MHz receiver. Could you please elaborate a bit on what you did in this conversion? Also, please advise what model number of MaxTrac you began with. There may be some aspect of the conversion that makes your receive radio especially vulnerable. If you have already tried bandpass cavity filters on the receiver input, with the radio inside a shielded box and all penetrations suitably filtered, and not seen any reduction in desense, then the offending signal must be on or very close to your desired receive frequency. That brings us back to a spurious or harmonic signal being generated by the FM broadcast transmitter, or perhaps there is an IM product being created between the FM station carrier and another transmitter that has yet to be identified. It may be instructive to use a good (i. e., well-shielded) spectrum analyzer with a bandpass cavity on its input to filter out everything but signals very close to your 900 MHz input frequency. This technique once helped me track down a alarm system motion detector that was operating around 900 MHz. Some spectrum analyzers are poorly shielded, and are practically useless when immersed in a high-RF environment. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com [mailto:Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com] On Behalf Of David Epley Sent: Thursday, November 22, 2007 9:17 AM To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com Subject: RE: RE: [Repeater-Builder] Receiver overload It is linked but there is only an STL link receiver at the site ________________________________ From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com [mailto:Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com] On Behalf Of n9wys Sent: Thursday, November 22, 2007 12:08 PM To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com Subject: RE: RE: [Repeater-Builder] Receiver overload Is the FM broadcast studio located at the transmitter site, or is it linked? If the studio is remote to the transmitter, it could be a harmonic of the studio uplink freq. But now I:m shooting in the dark. Mark - N9WYS ________________________________ From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com On Behalf Of David Epley Analyzer was connected to the receiver port of the duplexers. The noise floor looked good. The amount of degradation does not seem to change. There are 900mhz pager transmitters on site but none are on full time and I do not see any change as each one transmits. I can also have my transmitter turned off and the degradation is still here. ________________________________ From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com On Behalf Of Ron Wright David, Your problem might be harmonic related. Might do some calculator work. I can see no muliple of 104.9 related to your 2 frequencies or IF related. There are other 900 MHz stuff around. Would be good to get a spectrum analyzer on your receiver port, but know spectrum analyzers are not easy to come by. Might be noise floor emissions from the FM station which could be on your receiver input. Now this one would be a real problem. 73, ron, n9ee/r >From: David Epley >Date: 2007/11/22 Thu AM 07:32:46 CST >To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> >Subject: RE: [Repeater-Builder] Receiver overload> > >I just tried a pair of Celwave 8 inch bandpass cavities with no noticeable improvement. > > >David N9CZV > >From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> On Behalf Of Jim Brown > >David,try using one or two band pass only cavaties in >the receive side instead of the BpBr type. The BpBr >filters often do not discriminate against signals far >off the pass frequency, and you may not be getting >enough rejection out of your input cavities. > >73 - Jim W5ZIT > >--- David Epley wrote: > >> I have a repeater receiver overload problem I am >> trying to cure. The >> repeater is a 900mhz 927.7125/902.7125. There is an >> FM broadcast station 100 >> yards away 104.9mhz. The repeater works fine at >> another site. My transmitter >> is a Motorola Purc 5000 running 75 watts the >> receiver is a converted maxtrac >> 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I >> have 10 to 12 db >> degradation when plugged into 3 different antennas >> on the tower. When I use >> a 900mhz dish antenna pointed away from broadcast >> tower I only have 3 db >> degradation. I have tried 3 different maxtrac >> receivers, added 2 more BpBr >> cavities in the receiver side and used 3 pole >> filters in the receivers with >> no improvement. Today I looked at the signal level >> getting to the receiver >> at 104.9. To my surprise I was getting -8 dbm at the >> receiver. I believe >> this level is overloading the front end of my >> repeater. I was wondering if a >> stub cut for the broadcast frequency would work. Any >> thoughts would be >> greatly appreciated. >> >> David Epley, N9CZV >> Winchester, Indiana
