[Elecraft] K3 Harmonic Distortion

[Joe Subich, W4TV]

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 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
> Sent: Monday, September 01, 2008 1:33 PM
> To: elecraft at mailman.qth.net
> Subject: RE: [Elecraft] K3 Harmonic Distortion
> 
> 
> On Mon, 1 Sep 2008 12:38:31 -0400, Joe Subich, W4TV wrote:
> 
> >Jim is entirely correct although we will disagree a bit about
> >the need to keep the line out as low as he suggests.  My own 
> >measurements say the harmonic distortion is insignificant as 
> >long as the Line Out levels stay below .5V RMS. 
> 
> 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.  
> 
> >The headphone outputs are exceptionally clean as long as the
> >audio amplifier level is kept below 2V peak (1.4V RMS) and 
> >the output impedance is not too low.  In fact, noise in the 
> >audio amplifier (headphones) is 70 dB below the desired (CW 
> >at 500 Hz) signal +/- 250 Hz and 80 dB below the desired 
> >signal above that.  All harmonics are down more than 60 dB 
> >as long as the headphone level is not at levels that could 
> >damage hearing (> 1.4V RMS).  
> 
> YES! My measurements of the headphone output, taken at about 1 
> volt RMS, show harmonic distortion at about 0.02% and IM at less 
> than 0.1%. That is VERY VERY good!  1VRMS is LOUD! 
> 
> >The headphone output in the K3 is cleaner than any amateur
> >receiver I have seen and certainly better than the current 
> >crop from Ikensu or Yaecomwood. 
> 
> Yes. 
> 
> 73,
> 
> Jim
> 
> 
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft    
> 
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com