> -----Original Message----- > From: [email protected] [mailto:Repeater- > [email protected]] On Behalf Of Jeff DePolo > Sent: Monday, September 28, 2009 9:45 AM > To: [email protected] > Subject: RE: [Repeater-Builder] Two transmitter combining using a > duplexer? > > > Hey everyone, > > Thought about this yesterday...would it be possible to use a > > conventional pass/reject duplexer to combine two UHF > > transmitters into a > > single antenna? > > > > Example: > > Transmitter A is 453Mhz > > Transmitter B is 443Mhz > > Yes. Assuming the duplexer provides sufficient isolation to keep IM > products tamed down, it will work fine. A good UHF pass/reject duplexer > will give you 80 to 100 dB of isolation, which should be plenty. Just be > sure to measure the IM products to be sure. > > Most UHF pass/reject duplexers won't have a problem doing the 10 MHz > spread. > > > --- Jeff WN3A >
You only need about 10 dB of isolation between the two transmitters to do the "switching" to operate successfully. But you need more isolation to keep IM products down. A usual transmitter combiner has an isolator on each transmitter that provides around 30 dB IM protection followed by a pass cavity to provide the 10 to 15 dB of isolation for proper switching (impedance isolation). That pass cavity also serves as a low pass filter for the isolator harmonic products. Without an isolator on each transmitter additional isolation is needed to keep IM products down. As Jeff said, the duplexer should do fine. 73 Gary K4FMX
