The Devil is in the details... I glazed over the original post and just noticed.
> "David Epley" <[EMAIL PROTECTED]> wrote: > My transmitter is a Motorola Purc 5000 running 75 watts the > receiver is a converted maxtrac 800mhz radio. Using the converted Maxtrac Mobile might just be the fly in your soup. It's ability to deal with these type of receiver gremlins in less than ideal RF Locations is not so great. > Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db > degradation when plugged into 3 different antennas on > the tower. The question is... do you know exactly what that degradation is? As an example... is your receiver being blocked? is the problem based directly from the broadcast frequency? Sections of the receiver being overwhelmed by shear RF Levels and/or some specific section/stage within the receiver suffering from another issue? > 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 Place a band-pass cavity on the FM-Broadcast frequency (if you have one) or a 10 dB pad if you don't and park your service monitor (or similar animal) on the 900 MHz antenna(s) to measure how much on the broadcast channel RF (only) you have at the front end of your 900 MHz receiver. Since you can see differences in the problem by using different antennas (which have different isolation values from the problem signal), I would probably say there is possible hope you can resolve this problem. > added 2 more BpBr cavities in the receiver side and used 3 > pole filters in the receivers with no improvement. I would expect the Bp & BpBr cavity options to not bear the desired results... > 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. Bingo... well a partial bingo. Terms like receiver overloading and blocking can be throw out/around with really knowing the exact cause/source/problem. So be careful and don't go down a single path, which might be the wrong one. Per my above comment... what would be handy to know is the BC Station level at on all the 900 antennas and correspond those relative values to the "degradation" you measure from the receiver effective sensitivity (in operation on those antennas). > I was wondering if a stub cut for the broadcast frequency > would work. Probably not enough... you would normally need at least one (or more) very, very High-Q notch cavity (tuned to the BC channel) in place (on the 900 antenna system). > Any thoughts would be greatly appreciated. White wine is overrated... cheers, s.
