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One of the issues I faced with having two transverters that were to share a single transceiver running on 10 meters was switching between them.  Innitially I was considering to have separate transceivers but I really like my old IC-737 and couldn't decide if the 222 mhz or 1296 mhz transverter would be connected to it. Another issue I had was my fear of blowing up my transverters. If the power to the transverter was off or interrupted and I transmitted with the 737, its transmitter power would be dumped into the receive mixer of the transverter.... not a good thing! I was always paranoid about potential damage so I decided to try and reduce the probability along with providing switching between my transverters.

Both of my DEMI transverters are configured for a single transceiver output and have the 10 watt maximum optonal input circuit. I run my 737 with the power control at its lowest setting which is about 5 watts. I adjusted the transverter to be about 80% full power output at the 5 watt IF input level.

The circuit I designed below switches both the antenna connection and PTT line of the 737 transceiver to the transverters using a 3 pole two position rotary switch. The third pole switches a ground connection to a 12v relay corresponding to the transverter selected. The relay gets its +12v  from the selected transverters on-off switch. The relay interrupts the antenna connection to the transverter thus no transceiver RF power can get to the transverter unless it is powered on. It was necessary to add an additional RCA phono jack to each transverter and run a wire to the power switches to use this feature. Fortunately DEMI provides an extra hole on the rear of their current transverters that can be used.

A more careful ham would not need the protection of this fail safe feature!
A TRANSVERTER SWITCH  FOR MULTIPLE BANDS