Hi Guys,
I was testing out a Motorola 902 cell amp yesterday. While bench testing
the unit I noticed on the spectrum analyzer that there was what appeared to
be a serious spurious problem.
At first I thought it was the PA osciallting but a quick test revealed it
was coming from my older model DEMI transverter. Seems there is a lot of
gain peaking short of self oscillation in the 900 MHz TX upconverter. Has
anyone with an older model DEMI 902/903 transverter see this problem? The
spurious levels and amplitides are most sensitive (to probes, bypasses, and
finger farads) at the TX pin switch, but I can get it to fly by simply
touching center conductor on the TX N connect, where the TX path coax exits
the box.
Has anyone seen the need to go back and add zebra strips to the
feedthrough holes? Is this a job for some absorber materials?
It seems there is one gain stage that is marginally stable. Any thoughts
or suggestions would be appreciated.
Thanks...
73's Mike K9MK/5
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