Message-ID: <4CD729D1.3060706@iup.uni-heidelberg.de>
Date: Sun, 07 Nov 2010 23:36:01 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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Subject: Re: VLF: BBB-4-like receiver ready for first tests
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Hello Daniele,

> Q1: could such a response curve be suitable for reception of sub-9KHz 
> transmissions in the dreamers band or for chasing whistlers only?
>
The frequency response appears a little suboptimal to me since the mains 
hum would be even more amplified instead of attenuated. But i think it 
is rather useful to check the actual antenna configuration at its 
planned location. There you will see if and how much QRM bothered the 
system is. The final frequency response is not only a function of the 
amplifier but also to the location of the antenna. The lower frequencies 
are more attenuated by a lossy environment (trees, buildings). This 
effect can even be seen within the 0...24 kHz range. So maybe this 
amplifier frequency response can linearise the final frequency response 
so that the curve appears rather flat.

In my opinion it is useful to apply some band limiting. This can easily 
be done by a (or some) simple RC LPF and HPF. It is useful to exclude 
the strong LF/MF stations from the soundcard input and extremely strong 
mains hum components.

Recently i have been going arround on the roof of our institute (abt 30 
m above GND) with headphones, a netbook and a battery fed active E field 
antenna. There is a big difference if one is 2m or 4m or 6m distant of 
the buildings wall. Imagine the E field lines and/or the local field 
strength of that arrangement. As i was going to maximum distance (on the 
edge of the floor), the signal levels got so strong that the S/N of 
DHO38 decreased from 50 dB to 30 dB and i could listen to AFN (US BCD stn).

73 and good luck!

Stefan/DK7FC

> Then I created an external short-circuit on the BNC input connector 
> and looked at the output. I hoped to get some information about the 
> internal noise of the receiver. The resulting noise curve was 
> basically the same as the response curve when white noise from the 
> Agilent was applied at the antenna connector. I deduce that an 
> internal noise source exists in the receiver, close to the input stage.
>
> Q2: am I wrong? Is this normal (I mean: expected)? Should/could it be 
> improved by means of modifications in the circuit?
>
> Best regards
>
> Daniele
>
>
>
>

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Hello Daniele,<br>
<br>
<blockquote cite="mid:798586.46009.qm@web111901.mail.gq1.yahoo.com"   type="cite">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
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  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <p>Q1: could such a response curve be suitable for reception of
sub-9KHz transmissions in the dreamers band or for chasing whistlers
only?</p>
  </div>
  </div>
  </div>
  </div>
  </div>
  </div>
  </div>
</blockquote>
The frequency response appears a little suboptimal to me since the
mains hum would be even more amplified instead of attenuated. But i
think it is rather useful to check the actual antenna configuration at
its planned location. There you will see if and how much QRM bothered
the system is. The final frequency response is not only a function of
the amplifier but also to the location of the antenna. The lower
frequencies are more attenuated by a lossy environment (trees,
buildings). This effect can even be seen within the 0...24 kHz range.
So maybe this amplifier frequency response can linearise the final
frequency response so that the curve appears rather flat. <br>
<br>
In my opinion it is useful to apply some band limiting. This can easily
be done by a (or some) simple RC LPF and HPF. It is useful to exclude
the strong LF/MF stations from the soundcard input and extremely strong
mains hum components.<br>
<br>
Recently i have been going arround on the roof of our institute (abt 30
m above GND) with headphones, a netbook and a battery fed active E
field antenna. There is a big difference if one is 2m or 4m or 6m
distant of the buildings wall. Imagine the E field lines and/or the
local field strength of that arrangement. As i was going to maximum
distance (on the edge of the floor), the signal levels got so strong
that the S/N of DHO38 decreased from 50 dB to 30 dB and i could listen
to AFN (US BCD stn). <br>
<br>
73 and good luck!<br>
<br>
Stefan/DK7FC<br>
<br>
<blockquote cite="mid:798586.46009.qm@web111901.mail.gq1.yahoo.com"   type="cite">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div   style="font-family: times new roman,new york,times,serif; font-size: 12pt;">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div   style="font-family: times new roman,new york,times,serif; font-size: 12pt;">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <p>&nbsp;</p>
  <p>Then I created an external short-circuit on the BNC input
connector and looked at the output. I hoped to get some information
about the internal noise of the receiver.&nbsp;The resulting noise curve was
basically the same as the response curve when white noise from the
Agilent was applied at the antenna connector. I deduce that an internal
noise source exists in the receiver, close to the input stage.</p>
  <p>&nbsp;</p>
  <p>Q2: am I wrong? Is this normal (I mean: expected)? Should/could it
be improved by means of modifications in the circuit?</p>
  <p>&nbsp;</p>
  <p>Best regards</p>
  <p>Daniele</p>
  <p>&nbsp;</p>
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  <br>
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