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

[Leigh L. Klotz Jr WA5ZNU]

In the creeping features department, a similar high-pass filter (60Hz, 120Hz,
300Hz?) might be nice for PSK31 and other digimode hams who use panoramic
display software since they don't transmit at a fixed offset.
Leigh/WA5ZNU

wayne burdick wrote:
> 
> 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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