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

[k6dgw]

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?

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.

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?  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?

73,

Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn



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[Jim Brown-10]

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

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[Lynn W. Taylor, WB6UUT-2]

Jim,

Would you mind giving a few examples of these?  When I go looking I
often find things that are clearly far more than I want, or are actual
MIDI interfaces instead of USB sound cards.

73 -- Lynn

On 7/4/2017 4:03 PM, Jim Brown wrote:
> 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.
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