Rather than use a lossy expensive RF relay on the output of the DATV transmitter we can use a duplexer (for just 146 and 437 MHz operation) or a triplexer (for 146, 437 and 23cms operation) filter - as well as providing automatic band switching the duplexer (or triplexer) provides some bandpass filtering on the transmitter output!
The duplexr / triplexer can be a standard unit as we all use to run a dual band VHF / UHF rig in to a dual band antennae up one co-ax or they are very simple and cheap to build - links and circuits are available on these pages:
- I1WQR's page has several links to easily constructed duplexer designs - including one by Tony G3KTU.
- Very simple design from OH3TR
And of course there are loads of units you can buy from the normal sources: