[Elecraft] K3 Amplifier Drive Inconsistency

[Don Wilhelm]

Jim,

That sounds like RF getting into the audio.  Try moving the ferrites to 
the antenna feedpoint to choke off the RF on the coax shield.  Yes, the 
coax from a vertical needs a current choke.  In fact, you may need a 2nd 
choke at the shack entry point as well.  The coax will try to be an 
additional radial and that means it will have RF current on it - if not 
from the antenna itself, the radiation from the radiator may couple with 
the coax shield and cause RF on the shield (that is why the additional 
choke at the shack entry).

The KX3 has one characteristic that may cause confusion.  If the signal 
to the mic input is too large, the KX3 will shut down the audio gain 
giving the impression that there is not enough audio when in fact there 
is too much signal at the input.

73,
Don W3FPR


On 8/5/2019 9:23 PM, Jim Rhodes wrote:
> Last night I noticed I had little to no output from my KX3/KXPA100 combo
> especially on 40. I did a little experimenting and discovered that 3 turns
> of the transmit audio line through an unknown mix clamp on ferrite fixed
> the problem. Without it I was mildly affected on 20 and not at all on 15.
> With that choke in place I was stable on 40 and all other bands I tried. I
> am currently portable for work (in North Dakota) and am using a mobile
> antenna clamped to the top of a 6 ft tall wooden fence. Without the choke
> the ALC would go up when keyed, then drop off to near nothing. I know AFSK
> is becoming a more preferred method of generating RTTY, but I have never
> had this issue with FSK. So I learned a lesson about the little USB
> soundcard I use for portable ops.