I have done some experimenting with marginal S/N ratios as well. Still, it's
easier to copy signals with significant content in the 3-4 kHz range than those
with only 300-2.5k. I will be the first to tell you that it is far from a
scientific, but the extended silibance definitely added to my comprehension
under poor conditions. I also have done some "playing" with my transmitted
audio, and a majority of the time, when I focus my speech energy between 400
and 3500 Hz, I get noticeably better results than if I cut it at 2.5 or 2.6k.
I believe that is because when in "DX" or heavy QRM "Contest-Mode", most use
their IF shifts and heavily favor that range. Basically, I have 3.1k of
occupied BW to "shift around in", and I really think that's what makes the
difference. The existance of that slightly extended energy makes it "stand
out" at the receiving end. Tinkering with that here in my shack I have
confirmed that under marginal conditions, I can pick out the stations with
more upper frequency content than those without. All I can say is that when
there is significant noise & QRM, that extra couple hundred Hz of articulation
seems to make a difference.
Has anyone else experimented with that?
Joe, N3JI
----- Original Message ----
From: Tom W8JI <w8ji@w8ji.com>
To: Joe Isabella <n3ji@yahoo.com>; "Joe Subich, W4TV" <w4tv@subich.com>;
amps@contesting.com
Sent: Monday, July 3, 2006 4:01:29 PM
Subject: Re: [Amps] Maximum RF output in practical application: 4-250A
> On the contrary, Joe. I can prove humans can tell the
> difference between certain letters, words, and sounds with
> 4k of audio that you can't with 2.5k.
That's certainly true with very high S/N ratios on clear
frequencies, assuming the people have normal hearing and
speech.
I can prove the best S/N ratio and readability when signal
levels have less than 20dB S/N ratio occurs when SSB signals
are between 2 and 3 kHz wide, and that the most effective
weak signal communications occurs with about 2kHz bandwidth.
73 Tom
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