Tom,

If your running your 590 through a final amplifier, you might check the 
antenna relay in the amp.  I had trouble with my old als600 amp right after 
I got it and I had to adjust the antenna relay contacts and clean them so 
that my receive would always come back.  Just recently I started getting 
strange swr readings when transmitting with high power with my ALS1300 amp. 
I found that the output coax connector had gotten slightly loose on the 
chassis and after tightening the nut holding the connector to the chassis, 
problem solved.

Bob, K8LR, [log in to unmask]