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L-band Gear

I've been working on a Down East Microwave 1296 transverter setup for
several years.  One vexing problem:  the 2303 PA  (1/5 - 3 watt
amplifier) oscillates at nearly full output, with no input.  Providing
input reduces the spur amplitude, and provides a little output on the
channel frequency.  This is NOT local oscillator feedthrough, it happens
when there's nothing connected to the input except a 50 ohm load or the
input is open circuited, or the input is connected to the transverter.

I've replaced the module -- same symptoms.

I've replaced and added additional chip bypass caps on the various DC
lines.  Same symptoms

The power supply is filtered with a choke at the board.  Same symptoms.

I've placed the assembly in the open, in a shielded box, and in a
smaller shielded box.  Same symptoms.

So, has anybody else had this or similar problems? If so, how solved?
Any ideas???

Thanks & 73,


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