Date: Tue, 02 Mar 2010 20:29:36 -0000
To: rsgb_lf_group@blacksheep.org
From: "Roelof Bakker" <roelof@ndb.demon.nl>
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Subject: Re: LF: Re: 9kHz noise level
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Hello Paul,

Thank you very much indeed for the description of your elaborate VLF  
reception station.
There must have gone a lot of effort in building it.

I am looking for a simple way to detect the proposed test signals at 8.970  
kHz from Germany.
At my location loops are useless, due to local noise problems.
Using an E-field probe has been much more productive as a building acts as  
a Faraday Cage and will refrain local noise from inside the house to reach  
the outdoors. At 400 kHz the attenuation is around 30 dB. How this works  
at VLF has to be established yet. The main problem is to prevent local  
noise travelling over the shield of the coax cable to the antenna. CAT5  
network cable and isolating transformers have been used here as well to  
feed the antenna and transport the rf. An optical link will be tested on  
short notice.

I have a SPM-30 SLM which is fine for direct monitoring and is flat down  
to 200 Hz. However my PERSEUS direct sampling SDR is a much nicer tool as  
the sampled input can be recorded and processed later on. Today I have  
been testing sensitivity at VLF. At 20 kHz the attenuation is 2.7 dB,  
compared to 100 kHz. At 15 kHz it is 4.1, at 12 kHz it is 5.5 and at 8.970  
kHz it is 7.7 dB.

This is nothing dramatic as at 8.970 kHz the antenna noise is still 10 dB  
over the receiver noise.

I have also been looking into Spectrum Lab and feeding the antenna  
directly into an external EMU 202 USB soundcard, sampling at 192 kHz. At  
first sight sensitivity is down compared with the PERSEUS SDR, however my  
settings of Spectrum Lab are probably not optimised yet.

There is a link on the Spectrum Lab website to yours truly about VLF  
reception, but unfortunately it appears to be dead.

Best regards,
Roelof Bakker