On Sun, 16 Mar 2008 22:01:16 -0500, Bob McGraw - K4TAX wrote:
>Never run FULL OUT in PSK. About 30 watts from a 100 watt radio is
>about right. Run the computer sound card, line input and line output
>direct to the line in and line out connectors on the Omni V. Set the VOX
>delay for minimum, adjust the VOX sensitivity to max, adjust the sound card
>level to trip the VOX and adjust the mike gain for about 30 to 35 watts
>output. That's about as complex as it gets.
A bit of an oversimplification.
Two issues. #1 -- Power rating. PSK is a continuous mode, and most rigs must
be "de-rated" by at least 3 dB (run at half their CW power) to avoid damage to
the output stage.
#2 -- DISTORTION. This can occur by overdriving at the output of the computer
sound card (that is, the sound card itself distorts), overdriving the radio's
audio stage (the input stage(s) distort), and overdriving the output stage
(the final amplifier distorts). Any of these forms of distortion create
Intermodulation Distortion, which are extra sidebands of your signal that
interfere with other nearby signals. You will be a very unpopular guy if you
create distortion.
I recommend that sound cards be run at least 3 dB down from the point where
they clip, and that there be a resistive pad (voltage divider) of about 20 dB
(10:1) between the sound card and the radio. It is also critical that you turn
off any audio processing. Then turn up the audio only enough to get about half
power from the radio. This doesn't GUARANTEE that you'll be clean, but it's a
great starting point. The sound card in my IBM T22 (a pretty good one as
computer sound cards go) drops from about -30dB distortion to about -40dB
distortion just be reducing the output level that 3dB.
73,
Jim Brown K9YC
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