[Elecraft] Audio Hum in TX Data Mode

[Roger]

Good morning Conrad,

do you have the possibility to check the signal on an SDR or spectrum
analyzer with sufficient resolution. That might be helpful to determine the
origin of the noise and hence countermeasures.

73/Roger, DL5RBW

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Conrad PA5Y
Sent: Friday, September 27, 2019 11:27 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Audio Hum in TX Data Mode

I put up a new 6m antenna mainly for EME and I was so looking forward to
using my K3S. The RX is great, I run it in parallel with 2 other receivers
and it works very well on EME. However try as I might I cannot get rid of
some quite bad hum on the TX Audio. I am using USB and before you ask yes I
have got a low impedance ground from the PC to the K3S although removing it
makes absolutely no difference.  What did make a difference was moving the
radio away from sources of magnetic fields such as monitors. However I
cannot get rid of it completely. It also increases or at least changes when
I put my hands on the radio. 

I have a few other radios located nearby and close to a monitor, pc or PSU
and they do not suffer from this at all. Is this a common problem, is it a
bad ground in the audio path internally or magnetic coupling into an audio
transformer?

It is completely impractical for me to move my radios 10 feet from any
magnetic fields. Short of wrapping the radio in mu metal I really do not
seem to be able to fix this.

Any ideas? I have read and understood and followed Jim K9YC's advice and
this works perfectly for my other 3 radios. I am really at a loss.

73

Conrad PA5Y
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