Get better isolation of the VFO by putting it in a metal box.? Cut the output of the VFO by using a logic AND gate,? analog switches, or a series FET switch and a? shunt FET switch to greatly reduce the level.? Control the switches on VFO output with the transmitter PTT line.? Send the signal from the VFO to the xmtr over a coax cable.? Use a microcontroller or whatever to remember what frequency it was on and reprogram the VFO upon pressing PTT button.? There are probably other ways you could do it, this is just what immediately comes to mind.
How strong is the signal getting into the receiver, and under what conditions?? Barely detectable, or way over S9?? VFO board just laying on the table next to the receiver, or in a box with coaxial output and filters on all the power and control lines?
Jim Allyn - N7JA