[Elecraft] K3 Harmonic Distortion

[Leigh L. Klotz, Jr WA5ZNU]

It would be nice to see this problem with the the K3IO board addressed 
at some point.  It may be, as Jim K9YC has hinted, related to core 
saturation from low frequency components that could attenuated before 
reaching the board.  Or it may be that the transformers that fit in the 
space are as big as they can be, and a third-party outboard audio 
amplifier and isolation board is necessary, bypassing the transformers 
in the K3. 

But whatever the solution is, I'm looking forward to it, as using PSK 
with a waterfall display on the K3 requires me to ride the AGC, LIN OUT, 
and filters in a way that I didn't on the K2.

Leigh/WA5ZNU

> I've found that the LIN OUT port has typical third harmonic levels 
> around -45 dB from the fundamental, with the LIN OUT level set at 10, 
> the factory default. The headphone port, under the same conditions, 
> will show the third harmonic down about 70 dB or so at levels 
> appropriate for my Sony high sensitivity headphones. Cranking the 
> audio level up will cause higher distortion on the headphone port, but 
> only at levels that are impossible to listen to as they are so loud as 
> to  be unbearable.
>
> I've also seen some non-harmonic artifacts, particularly when very 
> strong signals are pumped into the K3's antenna port.
>
> Jack K8ZOA
>
> Julian, G4ILO wrote:
>> I think it was me who used the term "ghost" signals when referring to 
>> the
>> harmonically related CW traces I could see on the CW Skimmer display. I
>> probably would have been completely unaware of it if I had never 
>> tried this
>> program. It was only obvious as I was listening to CW with a narrow 
>> filter
>> and the "ghost" traces were appearing in the part of the waterfall 
>> that you
>> would be expect to be dark because it was outside of the passband. I 
>> would
>> agree with the suggestion that the harmonics are at a low level 
>> relative to
>> the main signal because they are masked by band noise when you open the
>> filter up. I don't think there is much risk of calling someone on the 
>> third
>> harmonic by mistake. I don't know what the voltage level of the line 
>> output
>> is but the traces disappear if you turn the level down to 2, which
>> unfortunately is too low for most sound card programs.
>>
>> I don't know if those same harmonics are present on the speaker or 
>> headphone
>> outputs, as distinct from the computer audio feed. I can only say that I
>> find the K3 audio exceptionally pleasant to listen to. I much prefer 
>> it to
>> the K2, or the FT-817, which are the only other radios I have. The only
>> other radio I have had that sounded as clean and low-distortion as 
>> the K3
>> was an IC-756PRO that I had many years ago.
>>
>> If the harmonics are down by the kind of amounts that others have 
>> measured
>> then the distortion figure is still within the specification for what 
>> after
>> all is not meant to be an audiophile quality hi-fi output stage.
>>
>> -----
>> Julian, G4ILO. K2 #392  K3 #222.
>> http://www.g4ilo.com/ G4ILO's Shack   http://www.ham-directory.com/ Ham
>> Directory    http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 
>> and K3   
>