First, my score: 15 meter single band at N4WW, WA6DGX, op
1224 x 117 = 430 k
I'm the proud owner of a half constructed W9GR DSP box, but I had
a chance to use a fully functional one this ARRL SSB test at
N4WW.
I can see how a short demonstration will leave you shaking your
head, feeling that you've just witnessed the biggest advance in
receiver technology since the superhet. On a signal that is a
couple of S-units above the noise, it makes the noise vanish -
completely. It really does reduced the fatigue of listening to a
noisy band.
But.... weaker signals start to sound very "tinny". I could get
used to it after awhile, but going from a loud to a weak signal I
felt that I noticeably lost some ability to copy.
Much worse, really weak signals vanish altogether. The person
who had constructed this particular box had made no provision for
passing the raw receive audio straight through, except by turning
off the main power switch. If you build one of these - DON'T DO
THAT! There is an "in/out" switch, but the audio is still
obviously passed through the A/D - D/A stages, just without being
filtered. Switching the filter to "out" would often cause a weak
signal to appear where none was apparent in the "in" mode, but
apparently even in "out" I was missing the really weak stations.
I know this because Red, K0LUZ, called me during the Saturday
afternoon doldrums and mentioned that had listened to me some
during the morning run, and several times he could hear a weak
station calling but I just called CQ. So, Sunday morning I just
left the phones plugged directly into the 930. Red listened
along again for about 15 minutes (this time he let me know he was
there - I sure wish he'd said something Saturday morning instead
of waiting until the afternoon :) and the result was
predictable - I heard at least as well as he did.
I'm going to go ahead and finish my DSP kit, but I will
definitely put in a switch that sends the raw audio straight
through without having to cycle the power (turning the box on
causes a few seconds of no audio while it resets). On the other
hand, make me an offer - I might sell it to you.
There are a few times when the noise filter is worth having, and
the notch filter is great for those times when you really need
it, but don't expect to use it routinely while running.
Ron WA6DGX
debry@sb.fsu.edu
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