Channel 12 = 204-210MHz. DTV is designed to look like noise so any mixes with it would sound like 'coarse static'
You didn't specify which frequencies your repeater is on also wheather the receiver uses high side or low side LO injection. As I recall Micors use a single 11.7MHz IF, assuming it the interference is going in there. If you are running low side injection this mix would be a real problem when the receiver is operated 215.7 to 221.7. Doesn't look like a problem, but you could also have a 3rd mix product coming from either an AM station (0.5-1.7 MHz) or 2 FM stations co-located that are X amount channel spacing from each other (0.3-20 MHz). Like this: 224.3 - (107.9 - 91.3) = 207.7 This works too: Transmitter - Channel 12 - Split = IF (1.6 + 11.7) + Channel 12 = 217.3 to 223.3 On 1/25/08, 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 > >
