Re: VLF: Carrier on 8270.0025 Hz

[Markus Vester <markusvester@aol.com>]

> Audible at 8270, not 16450. Can anyone explain why the sound is at the signal frequency and not the 2nd harmonic?

I "broke my head" a lot over that question. First I thought of a magnetic bias from earth's field but the effect turned out to be much too weak. My current assumption is that plastic surfaces aquire a static charge due to corona, and the AC voltage on the coil lets it vibrate in the DC electrostatic field.  

Best 73,
Markus

-----Ursprüngliche Mitteilung-----
Von: Paul Nicholson <vlf0403@abelian.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 16 Jan 2017 10:12 am
Betreff: Re: VLF: Carrier on 8270.0025 Hz

Stefan wrote:

> Since 22:45 UTC i'm running a plain and stable carrier
> Carrier stopped 00:05 UTC.

A strong signal! About 0.35 fT, 18.0 dB in 208uHz.

Could have sent 11 chars with the 80 minute signal.

vtread -T 2017-01-15_22:45,+80m /raw | # Extract signal, 3 chans
vtmix -c 0.866/-20,-0.5/-35,-0.85 | # Antenna mix and phase EQ
vtfilter -h bp,f=8270,w=3000 | # 3kHz bandpass
vtblank -a2.2 -d0 -t1 | # Blanking
vtmult -f8270.0025 | # Mix down to baseband I/Q
vtresample -r240 | # Drop to 240 samples/sec
vtraw -oa | # Convert to 3 column ASCII
ebnaut -r240 -dp16K25A -N11 -S2.8 -PS -c8 -L350000 -v

found rank 399 ber 4.0035e-01 Eb/N0 -0.6
M -2.546543181e-01 [***********] ps [ 2 30 30 30 30]

> but the BEEEEP is very loud!

Audible at 8270, not 16450. Can anyone explain why the sound
is at the signal frequency and not the 2nd harmonic?

--
Paul Nicholson
--