Its the PF0011 power module. That thing had horrendous internal gain, and
may need much additional bypassing of all the DC, shield can added, etc...
I "stabilized" mine by loading the input with a wire run parallel to the
input stripline, connected at the input pin. Still get 8W out, but no
pesky oscillation.
Might try a big block of absorber over the input end of the power module...
Couldn't hurt...
The "low power" 150W Motorola cell amps WILL oscillate if operated with
the cover off! If absolutely necessary to operate this amp with the cover
off, take precautions against oscillations destroying the PA... Monitor DC
drive with no RF applied, power out, and make sure it is connected to a
GOOD LOAD... Trust me, if tinkering and you set up a feedback path by
mistake, it will take off on you!
Eric
KB7DQH
> 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
>
>
>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|