[Elecraft] Signal tracing puzzler

[recarter at adelphia.net]

I thought my K2 receiver was dead, so I hooked up a signal generator to the antenna jack.  I setup the signal generator for about 7.1mhz sine wave and 140mv p-p into a 50 ohm terminator.  When I connect the signal generator to the connector, the signal goes away, just like it was grounded.  I pulled terminal 3 of T4 in the transmitter section and the signal comes back.  This transformer only has a couple of turns, so it seems reasonable that it would attenuate the signal.  After scratching my head for a while, I reconnected the transformer winding and connected to an antenna.  It seems as if the receiver works just fine.  I guess you can't argue with success, but I don't understand what is going on here.  Why would the signal from the signal generator get grounded at the antenna jack?

Thanks in advance
Rich - KE1EV