David, Have we ask if you can verify the problem is the FM transmitter???
73, ron, n9ee/r >From: Eric Lemmon <[EMAIL PROTECTED]> >Date: 2007/11/22 Thu AM 10:10:19 CST >To: [email protected] >Subject: RE: [Repeater-Builder] Receiver overload > >David, > >My first move would be to add a bandpass cavity in front of the receiver. >All cabling between the receiver and the RX output of the duplexer should be >double-shielded, with proper connectors on each end- no adapters, and no >nickel-plated connectors. The mini-UHF connector going to the MaxTrac >should be the only exception, but it's okay if very tight. > >If that doesn't cure the problem, then enclose the receiver in a shielded >box, and bring the signal and power leads out through feedthrough >capacitors. The MaxTrac radio has a lot of plastic in its case, and is >susceptible to signal intrusion. The best shielded box to use is a die-cast >aluminum enclosure from Hammond. > >I have assumed that the FM transmitter carrier is pure, without harmonics or >spurious artifacts. If the FM transmitter is radiating on a frequency close >to your desired input frequency, the above fixes may not have any effect. > >73, Eric Lemmon WB6FLY > > >-----Original Message----- >From: [email protected] >[mailto:[EMAIL PROTECTED] On Behalf Of David Epley >Sent: Thursday, November 22, 2007 7:02 AM >To: [email protected] >Subject: RE: [Repeater-Builder] Receiver overload > >The only transmitter that is on all the time is the FM broadcast My tx >plays no part in the noise > >________________________________ > >From: [email protected] >[mailto:[EMAIL PROTECTED] On Behalf Of Joe >Sent: Thursday, November 22, 2007 9:55 AM >To: [email protected] >Subject: Re: [Repeater-Builder] Receiver overload > >Can you give us a list of all the transmitters that are at/near the >site? Ones that are on the air all the time such as the FM station. >Does your transmitter have to be keyed to get the desense? > >73, Joe, K1ike > >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 > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
