13cm tvtr oscillation

Robin Szemeti - G1YFG


Has anyone any experience of this kit oscillating on transmit?

Even with no LO and no IF signal applied, the output pair of devices bursts into oscillation.   When you transmit an FM or reasonably strong SSB signal, it is enough to "swamp" the oscillation and make it appear to work correctly, but on quiet SSB sections it oscillates again.

If I remove the input coupling capacitor from the first amp, disconnecting it from the stripline feed that runs down the middle of the board, it becomes stable, but with the stripline connected, even if I remove the bias from the PIN diode T/R switch on the mixer it burst into oscillation still.

I'm beginning to think that having a 40dB gain amplifier with such a long length of exposed stripline across the board may not be the worlds greatest plan.

Any thoughts?  I'm tempted to construct a tin-plate box around the board, but I am not convinced it will help.

Best regards,

Robin Szemeti G1YFG

Robin Szemeti - G1YFG

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