[VHFcontesting] 902 MHz DEMI XVTR help fixing a PA spurious problem

Mike & Becca Krzystyniak k9mk at flash.net
Sun Feb 10 14:49:00 PST 2008


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





More information about the VHFcontesting mailing list