[AMPS] Solid State Amp Problem

[Steve Thompson]

-----Original Message-----
From: Paul Burton <burtonpt@ix.netcom.com>
To: amps@contesting.com <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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