BpBr duplexers only do wonders for the frequencies of intrest. That is the TX and RX frequencies. The space in between the 2 is somewhat attenuated, but the space outside the 2 frequencies is attenuated only -6 to -20dB depending on the frequency spacing, number of cavities and who made the duplexer.
This may seem alright, but -6dB down from 100 watts is still 25 watts. On 2/20/08, Cort Buffington <[EMAIL PROTECTED]> wrote: > > If the duplexers for each system are only 50 ohms at each receiver and > transmitter, then I should see 4 frequencies where there is a 50 ohm load, > and they are all different. Why would I need more than some sort of phasing > harness to connect the two duplexers to the single transmission line, > assuming the BpBr duplexers have enough isolation to keep the two repeaters > from bothering each other? > > On Feb 20, 2008, at 2:22 PM, DCFluX wrote: > > Isolators work with transmitters only. That would do nothing for > getting signal from the antenna into the repeaters. > > What you need is a diplexer. That is a low pass / high pass filter > network. These can be constructed with L/C high pass and low pass > filters, but that usually only has enough Q to work with a super wide > split, like VHF low pass and UHF high pass. > > It looks more like you need a pair of interdigital band pass filters. > > These can be tuned 5 MHz wide so the filter passes both TX and RX and > depending on the number of poles will be the isolation, I'd say 5 > poles should be around -60dB, 20 MHz out. > > They are kind of a pain to build as copper is expensive and aluminum > is really hard to weld, that aluminum solder crap never worked for me. > > And then they are a real nutbuster to tune, don't even try it without > a spectrum analyzer with a tracking generator. > > But before you spend any money, I would do a VSWR test with watt meter > and a hand held to see if the antenna is broad band enough to support > the 2 machines. > > > -- > Cort Buffington > H: +1-785-838-3034 > M: +1-785-865-7206 > > > > > >
