[Elecraft] RF feedback?

[K2QI]

Don, if that were the case wouldn't this problem manifest itself during a
constant carrier keydown, and not just in SSB mode?

Anyway, just to eliminate the feedline I took the dummy load outside and
connected the antenna feedline directly to it. I was previously using a
patch cable from the meter directly to the dummy load before.

Testing my system in this confiiguration shows no problems eitther, so it's
not something related to the way I have the coax run or the air-wound choke
I'm using.

Thanks for the information however.  I'm not sure if the amp is
oscillating.  I recently replaced the parasitic suppressors along with grid
chokes and mica caps and all seems to work fine but I'll keep my eye on it.

James K2QI

On Tue, Jul 14, 2009 at 6:41 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> James,
>
> Do not overlook the possibility that your amp is developing a parasitic
> oscillation.
> The behavior will be exactly like you describe - no apparent problem when
> driving a dummy load (because it is not frequency sensitive), but the amp
> will misbehave when driving a tuned load (like an antenna) which is
> frequency selective.  When the parasitic starts, you will see high SWR on
> your wattmeter.  Yes, such parasitic oscillation could be caused by RF
> pickup in the amp itself.  Your antenna is quite close for 1100 watts power.
>
> I don't have an easy answer for why it only shows up in SSB mode (unless
> the amplifier bias is changed when in SSB mode), nor why it is worse with
> reduced mic gain settings.
>
> 73,
> Don W3FPR
>
>