Couple of thoughts from one who is not to technically oriented. 1. Have you tried putting any notch filters between the duplexer and rcvr. to notch the TX freq. ? 2. Have you checked all of your cables and heliax connecters for proper installation ?
I only ask this because I was having erratic performance and desense on a 440 rptr. and found some bad duplexer cable connector installations when I started wiggling and moving them around. Another time while checking Fwd/Ref. power and SWR on o 160' peice of 1/2" heliax that I thought was good (and getting satisfactory readings on my Bird mtr.), I pulled the connectors of each end to inspect them. I found one connector had been improperly installed, the heliax shield had been twisted inside the connector to the point where it was almost touching the center conductor. Even though there was no direct contact between shield and the center conductor the RF on xmit. was desensing the rcvr. when the xmtr. keyed up. Reinstalling the bad cables and connectors solve the desense problem for me. -- Doug N3DAB/WPRX486/WPJL709 ---- Stu Benner <[EMAIL PROTECTED]> wrote: ============= Our group has substantial technical knowledge and experience, but we've been just about beaten down by a problem with our repeater. A brief overview of our situation follows. We have a 222 MHz repeater comprised of a converted Micor mobile, Telewave TPRD-2254 BpBr duplexer, AM-6155 PA modified for class C operation at 250W, and a DB-264JJ antenna at 80 ft. fed by 1/2' Heliax on a commercial FM broadcast tower . With the duplexer terminated into a load, we have about 1 dB degradation in sensitivity when transmitting. However, with the antenna connected to the duplexer, we experience in excess 15 dB of desensitization. We have eliminated other narrowband transmitters and analog TV transmitters as contributing factors. We are left with a channel 12 digital TV transmitter at an adjacent site as a key contributor to the problem. Our hypothesis is that we have broadband IMD products from the mix of our transmitter and the DTV transmitter that are appearing in and near our receiver passband. Is it a "rusty bolt" problem or is there some other non-linear component somewhere on the site or in our system that is the mixing point - we don't know. I'd be interested in beginning a dialog with anyone who might be able to give us some further insight into this problem. Regards, Stu Benner W3STU Boonsboro, MD
