[Elecraft] K2 + SignalLink: Setting gains for digital modes
Jim Brown
jim at audiosystemsgroup.com
Sun Apr 14 16:04:44 EDT 2013
On 4/14/2013 12:15 PM, Don Wilhelm wrote:
> I suggest you reduce the soundcard gain to the range of 1/2 to 2/3 of
> full which will allow more range on the SignaLink gain.
YES! Several times I've published a simple procedure for setting
computer sound card levels. It goes like this.
1) Find "cliip level" on the sound card. To do this, feed the sound card
output to a scope, get your RTTY or PSK program going, and push the
buttons that cause it to send tones to the radio. On the scope,
gradually increase the sound card output slider until you see squaring
at the top and bottom of the sine wave.
If you don't have a scope handy, listen on headphones as you gradually
increase the level until you hear the tones get "raspy" or "harsh" or
"brighter." With an AC voltmeter, look for the point when the reading no
longer increases as you increase the slider. Of these three methods,
the scope is best, your ears and headphones are second best. Use the
voltmeter method only if your hearing is gone and you don't have a scope.
2) Now that you've established "clip level," back off the slider by 6
-10 dB. 6 dB is half the voltage, 10 dB is about one-third the voltage,
easy to see on a scope or voltmeter. If you're using your ears, back off
the slider until it SOUNDS "half as loud." This works because human
hearing is logarithmic, and a reduction in level is HEARD as "half as
loud." The reason we go 6-10 dB below clip is that distortion in cheap
audio stages starts rising in the range of 6 dB below clip, so we make
our signals cleaner if we back it off by that 6-10 dB. .
This procedure works for ALL audio output stages and all radios, and is
not limited to Signal Link (which, by the way, is not that great a sound
card).
This procedure sets the level for the computer output. You still need to
follow instructions in the K3 (or KX3) manual to set levels in the radio
itself.
73, Jim Brown K9YC
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