Re: K3 "hum" problem - not the usual? [Try CONFIG:AFSK TX = FIL ON]
Posted by
wayne burdick on
Sep 28, 2009; 9:58pm
URL: http://elecraft.85.s1.nabble.com/K3-hum-problem-not-the-usual-tp3730769p3732157.html
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
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