Gentlemen and ladies, I have an RF device and an in-line amplifier (specifically an AMMC-6220 - http://www.datasheetcatalog.com/datasheets_pdf/A/M/M/C/AMMC-6220.shtml). Certain units develop gain spikes at the high-freq band. They are in very specific frequency locations, and vary in amplitude from unit to unit. Lowering the voltage to the amp eradicates the spikes. Raising it has the opposite effect. The bias voltage is well within spec. Another thing: playing with the input match to the amplifier has an effect on the spikes. However, the AMMC-6220 is (supposed to be) an unconditionally stable amplifier. This shouldn’t happen, assuming that what I’m seeing is oscillation. I’m stumped, and can’t do much except keep replacing this relatively expensive amplifier. The manufacturer doesn’t know what’s going on, nor do engineers a lot smarter than I. I can’t even seem to isolate the problem to a bad lot of amps. Any advice, theories, ideas, words of emotional support, would be appreciated.