[Elecraft] K3 "hum" problem - not the usual? [Try CONFIG:AFSK TX = FIL ON]

[Wayne Burdick]

The K3 has a CONFIG menu entry called "AFSK TX". If you set it to "FIL  
ON", a 400-Hz transmit-mode audio filter is inserted, centered around  
the mark/space tones. This is only available when the rig is set for  
AFSK A mode. It should be effective against low-frequency hum coming  
in through the mic or LINE IN connectors.

73,
Wayne
N6KR


On Sep 28, 2009, at 2:45 PM, Leigh L. Klotz, Jr. WA5ZNU wrote:

> Jim K9YC wrote:
>> Magnetic field coupling from the power supply to the K3's input  
>> circuitry,
>> probably due to the use of unshielded audio transformers in the K3.  
>> This
>> is a well known problem. One good band-aid is to go to the TXEQ1
>> settings and fully cut the three lowest octave bands.
>> ...
>> One of my neighbors had so much magnetically coupled hum
>> into the Line In transformer that it regenerated to full
>> output power when he tried to run RTTY in AFSK mode.
>
> Note that the upcoming firmware upgrade will reportedly eliminate  
> TXEQ in
> AFSK (and other audio-based digital modes), and it apparently may be  
> some
> time before another update provides true per-mode TX/RX EQ.  So people
> with hum will need another solution, except for the voice modes.
>
> I tried wrapping the component side of the transformers in a sheet of
> Mu-metal (actually, a competitor, not Mu-brand) and noted no  
> difference.
> It was probably a futile effort anyway as it didn't wholly enclose the
> transformer; probably I need to complain to Maxwell about this.
>
> Leigh/WA5ZNU