Operation with Antenna Change-Over Relays


The LT23S does not contain its own antenna change-over relay.  A built-in antenna change-over relay would only make it harder to connect a linear amplifier or a masthead (GaAs FET) pre-amplifier.  Instead,  each of these options may be supported with a pair of coaxial relays for each amplifier.


It is good practice to install a high quality coaxial relay near the antenna (say in the roof space) and to use a pair of coaxial cables.  The receive cable is connected to the ‘1296MHz in’ socket.  The transmit cable is connected to the ‘1296MHz out’ socket.


One side of the coaxial relay solenoid is connected to ground.   (The ground return is via the outer of the coaxial cable).  The other side of the solenoid is connected to the ‘+ Relais’ terminal with a single conductor wire.


On receive,  the coaxial relay is energised,  connecting the antenna to the input of the LT23S.  On transmit,  the coaxial relay is not energised connecting the antenna to the output of the LT23S.





Switching the coaxial relay induces a high voltage across the solenoid.  Make sure a diode (e.g. 1N4001) is connected across the solenoid. The cathode (marked with a ring) is connected to the positive end of the solenoid. 





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©  GJ Coyne & G Mussler  Dec-2003