Message-ID: <4CD83D22.50202@iup.uni-heidelberg.de>
Date: Mon, 08 Nov 2010 19:10:42 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
References: <798586.46009.qm@web111901.mail.gq1.yahoo.com> <6EEAA299A2084FACB780B4F9A675C31C@JimPC> <304036.93066.qm@web111919.mail.gq1.yahoo.com>
In-Reply-To: <304036.93066.qm@web111919.mail.gq1.yahoo.com>
Subject: Re: LF: Re: BBB-4-like receiver ready for first tests
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Hi Daniele, Jim, LF,

Am 08.11.2010 16:47, schrieb Daniele Tincani:
>
> Also consider that when I created a short circuit on the antenna input 
> of the rx (see Q2 in my e-mail), I got a response curve on SpecLab 
> similar to that I had with the Agilent, but with a peak level about 
> 30dB lower (about -107dB around f=2KHz on SpecLab).
This means that your generated noise level was to low and you have 
observed the soundcards noise, at least outside the region of 2 kHz. So 
just look at 9 kHz without the generator and then increase the noise 
gernerator level so that the noise increases say 20 dB.
> ------------------------------------------------------------------------
> *From:* James Moritz <james.moritz@btopenworld.com>
> *To:* rsgb_lf_group@blacksheep.org
> *Sent:* Mon, November 8, 2010 3:22:59 PM
> *Subject:* LF: Re: BBB-4-like receiver ready for first tests
>
>
> The filter rolls the gain off rapidly below about 1kHz and above about 
> 10kHz. So this would be OK for whistlers and 9kHz reception, but would 
> attenuate VLF utilities at higher frequencies.
>
Normally the MSKs are so strong that an attenuation of say 20 dB 
(compared to 9 kHz) will probably no problem. 20 dB gain reduction would 
not even mean 20 dB S/N reduction...

What i would worry about is the high gain arround 2 kHz, where the mains 
hum is dominant, even if the frequency response (without an input 
signal) would be flat. Maybe this could become a problem if the levels 
get so high that the amp stages become nonlinear and/or the soundcard input.

But just try what happend in reality!! In my experience it is a good 
indicator to see the diurnal noise levels having a minimum at arround 
8...10 UTC. If the level difference is about 10...15 dB (depending on 
the WX of course) it is a good first step to assume a sensitive RX. The 
rest can be seen in tests where a far field signal is generated on the 
Dreamers Band ;-)


73, Stefan/DK7FC

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Hi Daniele, Jim, LF,<br>
<br>
Am 08.11.2010 16:47, schrieb Daniele Tincani:
<blockquote cite="mid:304036.93066.qm@web111919.mail.gq1.yahoo.com"   type="cite">
  <style type="text/css"><!-- DIV {margin:0px;} --></style>
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><br>
  <div>Also consider that when I created a short circuit on the antenna
input of the rx (see Q2 in my e-mail), I got a response curve on
SpecLab similar to that I had with the Agilent, but with a peak level
about 30dB lower (about -107dB around f=2KHz on SpecLab).</div>
  </div>
</blockquote>
This means that your generated noise level was to low and you have
observed the soundcards noise, at least outside the region of 2 kHz. So
just look at 9 kHz without the generator and then increase the noise
gernerator level so that the noise increases say 20 dB.<br>
<blockquote cite="mid:304036.93066.qm@web111919.mail.gq1.yahoo.com"   type="cite">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div style="font-size: 10pt; font-family: arial,helvetica,sans-serif;">
  <div style="font-size: 13px; font-family: arial,helvetica,sans-serif;"><font   face="Tahoma" size="2">
  <hr size="1"><b><span style="font-weight: bold;">From:</span></b>
James Moritz <a class="moz-txt-link-rfc2396E" href="mailto:james.moritz@btopenworld.com">&lt;james.moritz@btopenworld.com&gt;</a><br>
  <b><span style="font-weight: bold;">To:</span></b>
<a class="moz-txt-link-abbreviated" href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a><br>
  <b><span style="font-weight: bold;">Sent:</span></b> Mon, November 8,
2010 3:22:59 PM<br>
  <b><span style="font-weight: bold;">Subject:</span></b> LF: Re:
BBB-4-like receiver ready for first tests<br>
  </font><br>
  <br>
The filter rolls the gain off rapidly below about 1kHz and above about
10kHz. So this would be OK for whistlers and 9kHz reception, but would
attenuate VLF utilities at higher frequencies.<br>
  </div>
  </div>
  </div>
  <br>
</blockquote>
Normally the MSKs are so strong that an attenuation of say 20 dB
(compared to 9 kHz) will probably no problem. 20 dB gain reduction
would not even mean 20 dB S/N reduction...<br>
<br>
What i would worry about is the high gain arround 2 kHz, where the
mains hum is dominant, even if the frequency response (without an input
signal) would be flat. Maybe this could become a problem if the levels
get so high that the amp stages become nonlinear and/or the soundcard
input.<br>
<br>
But just try what happend in reality!! In my experience it is a good
indicator to see the diurnal noise levels having a minimum at arround
8...10 UTC. If the level difference is about 10...15 dB (depending on
the WX of course) it is a good first step to assume a sensitive RX. The
rest can be seen in tests where a far field signal is generated on the
Dreamers Band ;-)<br>
<br>
<br>
73, Stefan/DK7FC<br>
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