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

["James Moritz" <james.moritz@btopenworld.com>]

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" <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
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

VLF_3D.jpg
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