Posted by
James Duffey on
Dec 27, 2006; 1:25am
URL: http://elecraft.85.s1.nabble.com/QRP-and-getting-above-the-noise-tp442397.html
CW signals can be copied by operators with even modest experience when
they are at the noise level, that is a signal + noise/noise ratio of 1.
Experienced CW operators can copy signals that are several dB below the
noise with little effort. If you have an oscilloscope or sound card, it
is useful to look around for weak signals and see how noisy a signal
you can copy. Turn the AGC off.
Pure tones, that is CW, are best distinguished from the noise at a tone
of around 500 Hz or so, and that is also the best frequency for
distinguishing two narrowly spaced signals. It is a broad minimum
though.
SSB signals need at least 10 dB and preferably 15 dB to 20 dB to be
copied. Some DSPs have filter algorithms that emphasize speech and
allow one to cheat on this number a bit, but not by a whole lot. Also a
number of years ago Ham Radio Magazine had details on a voice enhancing
frequency compensating network developed by NASA but I don't recall the
details or issue in which it appeared. I can look my Ham radios to find
it if you are interested though. - Dr. Megacycle KK6MC/5
--
James Duffey KK6MC/5
Cedar Crest NM 87008
DM65
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