[Elecraft] K3/K3s: Question(s) CW via audio into SSB transceiver

[Jim Brown]

On 7/4/2017 2:42 PM, Fred Jensen wrote:
> All the discussion raises a couple of questions for me:
>
> I believe [but do not really "know"] that Collins began this with the 
> KWM-2/2A and the S-Line.  The key line keyed an audio oscillator which 
> must have been very sinusoidal and free of noisebecause the CW 
> spectrum was very clean.  Is this true?

If Collins did it, it was probably very low distortion and low noise. :)

> When I run RTTY here at home [K3], I use AFSK from MMTTY and the 
> computer sound card.  I've looked at the spectrum and it's very clean. 
> I was under the impression thata single frequency from a sound card is 
> very sinusoidal with very low harmonic content and other artifacts 
> given that it's constructed from a nearly exact data stream.

That depends a lot on the sound card and how levels are set. Some are 
cleaner than others.  It's reasonable to assume that if it's built into 
a computer, especially a laptop, it ain't great.  About ten years ago 
when I was still using a Thinkpad  to run rather sophisticated audio 
measurement and analysis software, I looked carefully at the output of 
the sound card.  Just below clip, 2nd harmonic was only -30 dB re a sine 
wave tone; reducing the output level by 6 dB brought the second harmonic 
to -40 dB from the tone. I have long recommended the use of USB audio 
interfaces designed for use in small audio studios. Although I've not 
measured them for distortion, I would be VERY surprised if THD is 
greater than 0.5% just below clip, and that distortion will likely be 
predominantly 2nd and 3rd.

See http://k9yc.com/USB_Interfaces.pdf

> I know about the Windoze noises, mine are turned off.  If it works for 
> RTTY on my K3, why wouldn't CW also work equally well? 

It all comes down to the quality of the sound interface, how levels are 
set, and proper wiring between computer and radio.   Wiring is addressed 
in this set of slides.  Don't let the filename fool you -- this talk 
attempts to cover ALL aspects of power, grounding, bonding, and audio 
interconnections for ham radio.

http://k9yc.com/GroundingAndAudio.pdf

I've heard absolutely awful CW sent as SSB, but it's the result of 
complete ignorance of the concepts in these two pdf files.


> My sidetone is set at 580 Hz, a sweet spot in otherwise lousy hearing. 
> If I'm on USB with someone and send something on CW, I think he hears 
> it at 580 Hz.  Yes?

It depends on how his RX is set. Remember, in SSB mode, the frequency 
readout is the frequency of the suppressed carrier. If he's listening in 
SSB mode, yes. But if he's listening in CW mode, he'll need to tune 
either +/- 580 Hz from your SSB suppressed carrier frequency, depending 
on whether you're using USB or LSB. That's the difference that the  
settings Wayne talked about earlier today are designed to compensate. 
The CW in SSB mode adds or subtracts the audio tone frequency from the 
suppressed carrier frequency.

73, Jim K9YC