On Mon, 5 Jun 2006 11:37:20 -0400, Harold Mandel wrote:
>I want to get active on PSK-31, and cannot find info on
>receiving intelligence (versus garbage characters).
I strongly recommend the FREEware called PSK31, which is part of
the FREEware Ham Radio Deluxe suite of programs for radio control,
logging, and mapping. Works really well, absolutely painless to
use. It's written by Simon Brown, HB9DRV. Find it here:
http://hrd.ham-radio.ch/
The computer, using its audio card as I/O decodes received PSK31
and encodes your signal for transmission. In one screen window, it
is able to simultaneously decode and display a dozen or more
different signals! You then choose one of them to talk to, and the
encode/decode function switches to that frequency.
One VERY important caveat. Any distortion in the audio chain, as
well as the RF chain, will show up as another copy of your signal,
shifted in frequency from the main one. There are four common
places where this distortion can occur.
1) The output of your sound card. The distortion in most sound
cards, even "good" ones, begins to rise several dB below clip.
I've done some testing, and found that the distortion in mine (an
IBM laptop) drops from roughly -30 to -42 re: signal just by
dropping the output level by 6 dB. I look at distortion on an
audio spectrum an analyzer. You can do this before connecting the
computer to your radio.
2) The input of yor radio. For best signal to noise, your sound
card should run near the top of its dynamic range (see #1). This
means that you are likely to need a simple resistive pad (voltage
divider) at the input of your radio (even when it is called a line
level input).
3) Your transceiver's RF stages. PSK31 is a VERY efficient means
of transmission (at least comparable to CW), and a little bit of
power goes a long way. Again, running a few dB down will reduce
the distortion product (and for dissipation reasons, most rigs
want to be derated 3 dB for keydown modes like PSK31 anyway).
4) The same rules that apply to keeping distortion low on your amp
apply equally to PSK31. And remember, a little bit of power goes a
long way.
73,
Jim Brown K9YC
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