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Re: LF: Re: 9kHz noise level

To: [email protected]
Subject: Re: LF: Re: 9kHz noise level
From: "Roelof Bakker" <[email protected]>
Date: Tue, 02 Mar 2010 20:29:36 -0000
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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



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