[Elecraft] RF feedback

[Jack Regan]

Dick,

I have an 811-H connected to my K3 running 500 to 600 watts cw. I have
"problems" that might be similar to yours.  I get loud, fuzzy, cw tones on
both my noise canceling head phones my external speakers.  Both these items
are powered devices. One by a wall wart and one by an AAA battery.  When I
turn off the headphones I get interference free audio in the headset. When I
turn off the external speakers they shutdown so I have to unplug these from
the PHONES jack and use the internal speaker.  The internal speaker never
gets the interference. My neighbors were getting the same "cw" interference
on "powered" audio equipment.

I put low pass filters on both of my antenna feed lines at the output of my
external MFJ-989D tuner. Perhaps I should put them between the amp and the
tuner! Anyway this seemed to help but in fact it only shifted the problem
frequencies from 20 to 40 meters. The low pass filters did cleanup TV
interference but not the audio level problems!


My next step will be to properly ground all the gear! Yes, I am guilty! In a
rush to get on the air for ARRL-SS and CQ-WW I did not properly ground the
new amp and tuner!  I'll let you know if this fixes the problem.

I had investigated chokes myself but did not want to get them until I
properly grounded all my gear!

BTW, the amp, tuner and K3 did well in the contests!  I easily got the last
5 states I needed for WAS. All have been confirmed either by card or LoTW. I
also got 8 new countries, 3 of which are already confirmed!  Power helps! A
lot!   

I let you know the grounding works out.

-----Original Message-----

In a message dated 12/5/2008 9:05:02 A.M.  Pacific Standard Time, 
rlindzen at MIT.EDU writes:
I'm running the K3 with an  Ameritron AL800 and a Steppir 3 element 
with 40m dipole add-on.  I have  a severe though intermittent feedback 
problem on 40m that I did not have  with an Icom 751a.  The feedback 
only occurs when I'm using the amp  (even with very low drive).  I've 
common core choked virtually every  lead with ultimately no luck.  I'm 
using the Elecraft hand mike.   Is there a known problem 
here?  Otherwise, I'll just keep  searching.

Dick

++++++++++++++++++++++++++++++++++++++++++++++++++
Have you tried other bands?  What Version Firmware are you  using?
 
I have a problem that may also be RF feedback related. I occurs only on 40M

and only when I exceed 80 W to my Dipole antenna. No problem full power up
to  
120 watts into Vertical or any other band. Problem started immediately after

upgrading FW to V 2.46. I have a couple upgrades to do on the rig including 
the  AGC upgrade, which I have held off making until my Sub Receiver
upgrade. 
Since  that arrived a few days ago I will be doing all upgrades and the 
subreceiver  install this weekend. I don't plan on any changes in FW other
than 
activating  the KRX3.  I will then test the 40M issue. I do not have a good
earth  
ground on the K3 nor am I running any form of Amp. But, the rig has worked  
perfectly since it was installed a year ago and the ATUs have always
provided a  
good match in the 1.X:1 range on both Vert and Dipole including 160M, 30M, 
12M,  17M in addition to the usual 5 bands the Ants are designed for.
 
Al WA6VNN