> The issue is that I want to add a same-band remote base to an > existing repeater. The main problem is that the remote base is a > transceiver and I can't find a way to provide proper isolation > to/from the repeater.
It's not a problem if the hardware is done smart and right. Even fairly close spaced remotes can and do work. > Here are the frequencies, but it looks like it really doesn't matter > all that much. The repeater transmits on 443.300, receives on > 443.800. We're using a typical UHF pass-reject duplexer with > about 70 db of isolation between those two freqs. The remote > base will transmit on 444.225 and receive on 449.225. Aside from what we see as a possible typo, you'd be running the remote base radio almost 1 MHz away from the repeater. Are you sure the remote base frequencies are indicated right? Don't you want to tx high and rx low... but I know different areas of the country flip the UHF Band back and forth... > I can put two antennas on the tower, but my horizontal space > will be less than 20 feet. Vertical spacing is butta' (better) but horizontal spacing is also usefull. The only practical "free lunch" you get when trying this type of setup is the isolation provided by the vertical distance between antennas. > From the pile of spare parts, I have a multitude of UHF band pass > and notch filters. I would also not be opposed to adding something > like a pass-notch duplexer if there is a way to configure it to > work. First: Put an at least one additional notch in the repeater receiver path set up to reduce (notch) the remote base radio tx frequency. > From my testing, it seems that the real issue is that the remote > base is a transceiver and there is pretty much no way to add > anything except notch filtering. Adding band pass cans will filter > either the tx or the rx, but not in any combination (that I can > find) to do both. Yes you can... let me throw this out just so everyone can toss it around in their noodle. Why can't you set up 2 or 4 band-pass bottles as a basic duplexer on the remote base frequencies. Then instead of using "each side" of the duplexer as the normal or expected duplexer tx or rx port... make up another coax T just like the antenna T side of the duplexer and tie the two duplexer ports back into one path on the other side of the bottles. Wheels turning yet..? > If the remote base had a separate tx and rx, then a band pass can > with a notch can (on the repeater freqs) on each side would probably > work fine. > Anyone have a good solution? Yeah, but the California Lotto hasn't found me yet... > Dwayne Kincaid > WD8OYG Other things are possible... but you should also consider using as low as possible power on the remote base radio and depending on the various receiver(s) quality... you might need some additional filtering. cheers, skipp
