[Elecraft] K3 with SDR-IQ and external antenna for SDR-IQ?

[Edward R Cole]

KD7YZ Bob:

Not difficult to do with the K3.  Connect to the KEY OUT connector 
with wiring to the ground side of a 12v coax relay with a 50-ohm term 
on the NO coax connection.  Connect the SDR-IQ to the relay common 
coax connection and antenna to the NC coax connection.  The K3 will 
cause the coax relay to switch the SDR-IQ into the load when the K3 transmits.

The SDR-IQ has to be on a separate antenna from what the K3 is 
connected, to ensure no RF goes to the SDR-IQ.

If you already are using the KEY OUT for controlling something else 
then a NPN transistor is needed to isolate the relay coil from the 
other device.  The NPN will invert the logic so you may need another 
transistor stage to maintain the same logic.  Alternately you can 
make an logic isolator with two diodes such that current from the 
relay does not flow to the other device but only thru the K3 KEY 
ckt.  (sounds more complicated than it is).

73, Ed - KL7UW