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LF: Re: AW: 9kHz loop/preamp for soundcard receiver

To: <[email protected]>
Subject: LF: Re: AW: 9kHz loop/preamp for soundcard receiver
From: "James Moritz" <[email protected]>
Date: Wed, 10 Mar 2010 23:37:26 -0000
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Dear Stefan, LF Group,

So far, I have not had time to make any detailed measurements and comparisons - but the "quick look" screen shot attached was taken at my home QTH on Sunday when both the QRN and the local mains QRM were exceptionally low for a short period. The frequency range is 5kHz - 20kHz, and the FFT resolution is about 1.5Hz. The 3D waterfall shows the alpha beacon "spikes" rather well. The continuous line just above the highest alpha frequency appears to be a 15.625kHz TV line timebase. Normally, frequencies below about 10kHz are filled with 50Hz harmonics well above the QRN level, although the level varies greatly. I did briefly try the RX at a /P location this afternoon - mains noise was much lower than at home, but the QRN level was much higher today than in this screen shot. However, since the 50Hz harmonics mainly produce narrow-band spectral lines in the waterfall, these should not be a great problem for receiving very narrow band QRSS-type modes, providing the frequencies do not coincide exactly.

I'm not sure what to do about the TX side of 9kHz yet - I want to look in a bit more detail at the technical problems that need to be overcome before making a proposal for a NoV to Ofcom.

Cheers, Jim Moritz
73 de M0BMU

----- Original Message ----- From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Wednesday, March 10, 2010 9:43 PM
Subject: LF: AW: 9kHz loop/preamp for soundcard receiver


Very nice Jim!

And now, since you are /p, which background noise level (or SNR of the alpha stns) do you achieve when you go away from the house? Is that a big difference or just some dB?

I am happy that you are also interested in the 9kHz dreamers band! :-)

Will you try to do anything on the TX side next?

73, Stefan

Attachment: VLF_3D.jpg
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