[Elecraft] K3 Harmonic Distortion

[Berni G0IDA]

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 
>  
>
>
>
>   
>> -----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
>>
>>
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