Paul: Have you considered possibility of r.f. getting into p.s. or maybe
even on the case of the radio. Do you have a balun on the antenna? I
would look into the possibility of r.f. on the outside of your coax or
poor grounding system. Could the p.s. be "motor boating" at 6khz rate.
Try changing the coax length to your antenna looking for any change in
the spurs. 73, Dan, N5AR
Steve Thompson wrote:
> -----Original Message-----
> From: Paul Burton <burtonpt@ix.netcom.com>
> To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
> Date: 20 May 1999 00:52
> Subject: [AMPS] Solid State Amp Problem
>
> >
> >My Icom transceiver recently started putting out spurs
> every 6Khz above
> >and below my carrier at fairly strong rf level. I have
> verified this
> >with a spectrum analyzer and also that the spurs are not
> present at the
> >input to the power amp board. These spurs are not present
> when driving
> >into a dummy load, only into an antenna with about 1.3/1
> SWR. The
> >problem seems to be related to reflected power. Can
> someone
> >knowledgable in solid stare amps confirm that this might be
> caused by
> >bad final transistors? If not, what might cause it. I
> appreciate any
> >help/comments.
> >
> >73 Paul AA6Z
>
> It could be quite a number of things, including duff
> original design. If the output power and current are ok into
> 50 ohms, the transistors are likely to be ok - usually they
> either work or blow although I have sometimes (rarely) seen
> injured ones.
>
> One thing to check is whether it is a low frequency
> oscillation modulating the output (put a 'scope on the PSU
> and bias feeds), or IMD from a hf or vhf oscillation (probe
> with the analyser before the harmonic filters). Do the spurs
> appear on all bands, do they change frequency with changing
> load conditions?
>
> Steve
>
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