[RFI] RF Feedback - FL7000 AMP

Jim Brown 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
>> SSB

>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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