[Elecraft] K3 Tune carrier with hum

[David Gilbert]

Do you have a computer connected to your K3, either via the audio 
connections or the RS-232 cable?  If so, make sure that you have the 
chassis of the K3 really well bonded to the chassis of the computer.  I 
had a similar problem (not only in TUNE, though) and received a few 
on-the-air reports about it, so I listened with a second rig (powered by 
a battery for ground isolation) while transmitting with the K3 into a 
dummy load.  I could hear the hum, which wasn't even a clean 60 Hz (more 
like a spectrum of multiple tones 30 Hz or so apart), and I could also 
see the hum using Spectrogram while feeding the audio from the second 
rig into the sound card of the computer.

I assumed I had a ground loop somewhere and began disconnecting other 
equipment (amplifier, SWR bridge, UPS, etc) one by one but nothing 
worked ... not even operating the K3 off battery power.  It wasn't until 
I finally disconnected the computer that I no longer heard the hum in 
the second rig.  I tried using a simple 18 inch clip lead to bond the K3 
chassis to the computer chassis and that helped, but it required a 12 
inch piece of RG-213 copper shielded braid to make the problem really go 
away. 

73,
Dave   AB7E



Ulrich Quandt wrote:
> Hi,
>
> on my K3 the tune carrier is modulated by a hum noise. If i press the tune
> button i can hear this noise with an independent receiver.
> It has nothing to do with my power supply and the problem appears between 1
> to 100 watts.
> It seems that the noise is generated inside the K3.
>
> I have this noise only during tune, all other transmitting works flawless.
>
> Any idea ?
>
> 73 de Uli (DL4YCM)
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