[Elecraft] K3 Distorted Audio On Transmit

[Don Wilhelm]

Dave,

Audio distortion on only 1 or 2 bands is usually a symptom of RF in the 
Shack.
That is confirmed by the fact that all is well on a dummy load.
The best place to cure it is on the antenna feedline.
If you do not have a good current balun at the antenna feedpoint, add one.
If you have a few feet of slack in the feedline, I would make 5 turns of 
the coax through a stack of 5 or 6 FT240-31 ferrite toroids.  Do that at 
the shack entry point or just inside the shack.  See the information in 
K9YC's paper on RFI for a photo - http://audiosystemsgroup.com/RFI-Ham.pdf
The toroids are available at Mouser or from Diz at 
http://www.partsandkits.com

73,
Don W3FPR

On 3/1/2014 12:08 PM, dave_w0ru wrote:
> I have a K3, P3 and KPA500. Last night I was encountering some high SWR. The
> K3 has the KAT3 internal 100 watt antenna tuner. I do not have the KAT500
> tuner. If the SWR was too high, the KPA500 indicated a fault and I went back
> to 100 watts with the K3. I tried bypassing the KAT3 to see how the SWR
> looked. The K3 started producing extremely distorted audio when I
> transmitted (I was listening with my headphones). The audio sounds like a
> loud roar. This only occurred on 20 and 30 meters at about 50-100 watts
> output using upper sideband (yes, I know we can't legally use USB on 30
> meters, I just briefly keyed the PTT). The other bands were fine. Today I
> found the problem does not happen when I use a dummy load. The K3 schematic
> shows`there is a low-pass filter for 20/30 meters. I am just trying to
> figure out if the high SWR caused damage.
>
>