[RFI] RF Feedback - FL7000 AMP
jim at audiosystemsgroup.com
Wed Aug 19 12:36:16 PDT 2009
On Wed, 19 Aug 2009 14:42:17 -0400, Tony wrote:
>> It's not an RF feedback issue. The FL7000 is super touchy on overdrive in
>I'm glad you mentioned this because the protection circuit was tripping on
>several bands before I installed a line isolator on the feed lines.
I wouldn't rule out RF feedback. My two FT1000MPs have a pin 1 problem at the
mic connector that causes RF feedback on 75M and 15M. Measurements of that
pin 1 problem show a broad peak around 5 MHz and a narrower one at 21 MHz. I
eliminated it with five turns of the mic cable around a #43 toroid. MOST ham
gear is built with pin 1 problems, primarily on non-RF cables (but I've also
seen some BNCs isolated from the chassis as well), so any RF in the shack can
light them up. See my RFI tutorial of detailed advice on winding chokes to
kill the current. http://audiosystemsgroup.com/RFI-Ham.pdf
Another thought. Are you using and depending on ALC to set your drive level?
That's a very bad idea, and leads to broad signals. ALC is OK as "belt and
suspenders" protection to prevent overdrive when something goes wrong, but in
normal operation, drive level should be set with the output power control of
the exciter, not with ALC.
Jim Brown K9YC
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