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Date: Mon, 11 Jan 2010 18:41:38 +0000
Message-ID: <fc7eccec1001111041q672a5054w4ce5b1779e978ba6@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: CW S/N abilities
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Good....
Confirms exactly what I assumed.
5dB in 24Hz (which is about the same effective bandwidth of a good pair of
ears)  is -15dB S/N in 2500Hz

Its interesting, too, that SSB is readable at far lower S/N ratios than
might normally be expected.  My SSB contesting ears, which have had practice
mostly with AWGN on the microwave and VHF bands, but nothing like as good as
the experienced ops, can read callsigns and reports - ie preformatted data -
at a S/N in the SSB bandwidth of around -10 to -5dB.   If we assume a S/N of
+5dB is needed for incoherent detection, that suggests an effective aural
bandwidth around 100 - 200Hz

Considering the whole human evolutionary process has been geared to
listening to voice -ike sounds, its not really surprising that we apply
considerable adaptive filtering to the voice channel to get an efcective
bandwidth so much lower than the actual band.    So the human voice is a
spread-spectrum system.

Andy
www.g4jnt.com


2010/1/11 Roelof Bakker <roelof@ndb.demon.nl>

> Hello Andy,
>
> The bandwidth of the SPM-30 was set to 24 Hz.
>
> 73,
> Roelof
>
>

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<div>Good....</div>
<div>Confirms exactly what I assumed.=A0=A0 </div>
<div>5dB in 24Hz (which is=A0about the same effective bandwidth of a good=
 pair of ears)=A0=A0is -15dB S/N in 2500Hz</div>
<div>=A0</div>
<div>Its interesting, too, that SSB is readable at far lower S/N ratios th=
an might normally be expected.=A0 My SSB contesting ears, which have had=
 practice mostly with AWGN on the microwave and VHF bands,=A0but nothing=
 like as good as the experienced ops, can read callsigns and reports - ie=
 preformatted data - at a S/N in the SSB bandwidth of around -10 to -5dB.=
=A0=A0 If we assume a S/N of +5dB is needed for incoherent detection, that=
 suggests an effective aural bandwidth around 100 - 200Hz</div>

<div>=A0</div>
<div>Considering the whole human evolutionary process has been geared to=
 listening to voice -ike sounds, its not really surprising that we apply=
 considerable adaptive filtering to the voice channel to get an efcective=
 bandwidth so much lower than the actual band.=A0=A0=A0 So the human voice=
 is a spread-spectrum system.</div>

<div>=A0</div>
<div>Andy<br><a href=3D"http://www.g4jnt.com/" target=3D"_blank">www.g4jnt=
.com</a><br><br><br></div>
<div class=3D"gmail_quote">2010/1/11 Roelof Bakker <span dir=3D"ltr">&lt;<=
a href=3D"mailto:roelof@ndb.demon.nl" target=3D"_blank">roelof@ndb.demon.n=
l</a>&gt;</span><br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">Hello Andy,<br><br>The bandwid=
th of the SPM-30 was set to 24 Hz.<br><br>73,<br><font color=3D"#888888">R=
oelof<br>
<br></font></blockquote></div><br>

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