[Elecraft] K3 Harmonic Distortion

[Jack Smith]

I've made a number of measurements on the K3's audio output a few days 
ago in CW mode and again today, this time with two close spaced signals 
inside the SSB filter as well as a single tone.

Yes, there are 3rd and other odd-order harmonics and, to a lesser 
degree, even order harmonics.

However, these harmonics are down between 45 and 50 dB from the desired 
signal in most instances. That's quite a bit of odd order harmonic 
suppression, well under 1% THD.

I can see intermodulation products and in-band artifacts with the AGC on 
and quite strong signal levels. These are also quite a bit down from the 
two tones, but certainly differ from the same signal levels applied to a 
receiver with analog detection stages.

I cannot hear an objectionable beat note or rough audio, but I'm afraid 
that I fall into the category of being old enough to not have great high 
frequency hearing.

I'll put some of the audio spectrum analyzer captures up on my web site 
later  today or tomorrow.

Jack K8ZOA


Berni G0IDA wrote:
> Thanks everyone for the replies.
>
> I just would like to put this thread back onto its tracks..... The 
> problem is with CW (although SSB does suffer too) and the main problem 
> is that I can hear the 3rd harmonic which when mixed with the 
> fundamental makes a rough note on CW especially when tuning away going 
> up in frequency.
>
> I only used the waterfall program to confirm and to see at which 
> harmonic it occurred and line levels, AGC, PC cards etc...etc... have 
> no baring on this as I'm not measuring anything, just confirming that 
> it is there.
>
> I compared 2 K3s and both had the same effect.
>
> I'm using a Hiel headset to listen to CW it is also noticeable on the 
> main speaker but less so due to its design.
>
> When confirming on the waterfall and indeed with my ears the rig is at 
> default setting & no amount of tweaking helps. Even with 1KHz of 
> filtering a 3rd harmonic is present.
>
> K9YC:
> 1) Yes
> 2) Line level is irrelevant as I'm just confirming that it is there 
> and at which harmonic so as to give feedback to the reflector.
> 3) as above.
>
> N4LQ:
> I agree with you, nothing seems to help and I've never had this with 
> the FT1000MP or my recent Mk v.
>
> W4TV:
> I envy the K3 you have.... as there is 3rd product distortion and 
> never had this on any other rig... could there be a "bad batch" or K3s?
> Just like to re-iterate that the thread is not about how to set up 
> your PC/LINE OUT or IN not to get distortion, it is about 3rd harmonic 
> distortion present on the headphone socket and speaker with or without 
> default settings!
>
> Jim:
> PSK + RTTY might have its own problems & its not part of my 
> discussion, I'm trying to concentrate this thread on just one mode CW 
> where this problem is significant as at times it is unpleasant to 
> listen to. SSB also has this unpleasant distortion.
>
> There is one option a friend suggested.... wait until I get older and 
> the hearing drops off in frequency.... at the moment it seems the only 
> option..hi..hi..hi..
>
> 73s
>
> Berni
> G0IDA
>
>
>
>
> Jim Brown wrote:
>> On Mon, 01 Sep 2008 14:30:45 +0100, Berni G0IDA wrote:
>>
>>  
>>> I hope there is a cure for this as it's frustrating listening to CW 
>>> with this sort of distortion.
>>>     
>>
>> There are three things you should do.
>> 1) Make sure that the AGC is on, and that the CONFIG AGC settings are 
>> at the defaults. 
>> 2) Reduce the LINEOUT GAIN (on the CONFIG menu) to a value less than 
>> about 4. This prevents distortion that could occur in the output 
>> transformer.
>>
>> 3) Adjust the input gain of your computer so that you have enough 
>> signal for the decoder to function, but not enough to cause distortion.
>>
>> This should correct any problems.
>>
>> 73,
>>
>> Jim K9YC
>>
>>
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>