[Elecraft] Pre for the Rx ant only?

[Gary Smith]

when I am using my Rx ant into the sub receiver, I click sub and then 
hold Rx-ANT till it says AUx. I have my beverage connected to the BNC 
port below ANT2.

If I want to have the K3 preamp on for this Rx antenna but not have 
it on for the Inverted L, how do I engage the second receiver so it 
alone has the preamp engaged? I don't want the noise from my transmit 
antenna amplified.

I am mostly working diversity.

Thanks,

Gary
KA1J