[Elecraft] K3 Harmonic Distortion

[Jim Brown]

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