[Elecraft] K3 Harmonic Distortion

[Joe Subich, W4TV]

> Anyway, the "noise/distortion" is still there coming out of the 
> headphone socket.

The spectrum display you sent me shows an excessive level of 
50 Hz harmonics - some 15 dB above the noise floor and only 
40 dB below the desired signal from 150 Hz to above 3 KHz.  
That strongly indicates serious grounding issues, power supply 
filtering problems, improper power supply decoupling and/or 
soundcard instability.  I suggest you read K9YC's information 
on interfacing and RFI www.audiosystemsgroup.com/publish.htm 
and resolve that noise issue first.  I have seen the K3 audio 
output "go spurious" when presented a bad load or encountering 
regeneration (feedback from powered speakers) due to bad grounds.  





> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Berni G0IDA
> Sent: Monday, September 01, 2008 7:13 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Harmonic Distortion
> 
> 
> Yes indeed it would be a sorry situation if an operator can't 
> tell the difference between a desired signal and an audio 
> harmonic, fortunately 
> my thread is not about that.
> 
> Anyway, the "noise/distortion" is still there coming out of the 
> headphone socket.
> 
> Berni
> 
> Joe Subich, W4TV wrote:
> > Jim,
> >
> >   
> >> Insignificant depends on the decoder, what you are decoding (PSK
> >> or RTTY), band conditions, and the operator. If a PSK operator is 
> >> using the IF with a broadband setting and tries to work a signal 
> >> that's really a harmonic, it won't work -- he'll be transmitting 
> >> on a frequency displaced from the signal he thinks he's working 
> >> (displaced by 2X the audio frequency of the actual signal if it's 
> >> a third harmonic, 1X if it't the second harmonic). If it's a 
> >> crowded RTTY contest, there can be lots of big signals creating 
> >> that IM. Or the operator could be using a narrow roofing filter 
> >> and those other signals are not there or heavily suppressed, so 
> >> can't cause IM.
> >>     
> >
> > It would be a sorry situation if an operator can't tell the
> > difference between a desired signal and an audio harmonic down 
> > 50 dB.  K3_Line_out.jpg shows the line out spectrum of my K3 
> > at 1 KHz, Data_A, 2.8 KHz 1st IF filter and 4 KHz filter.  The 
> > third harmonic is -62 dB and the fifth harmonic is - 80 dB. 
> > See: www.microHAM-USA.com/Downloads/K3_Line_Out.jpg.  
> >
> > A typical waterfall does not show the spurious signals at the
> > soundcard input (noise on the cables) which is well below the 
> > "band noise" - typically around -60 dBu.  
> >
> > 73,
> >
> >    ... Joe, W4TV
> >  
> >