[TangerineSDR] [HamSCI] Merry Christmas! SAQ Grimeton Christmas Eve Transmission

Jonathan emuman100 at gmail.com
Sat Dec 25 19:31:59 EST 2021

Hi John,

Thank you! I cannot thank you enough for this great idea to filter it
further. There is a lot of local interference. vtfilter’s bandpass filter
is a brick wall filter and when I tried to filter the spectrum further, I
didn’t get a good enough result. The bandpass filter that sox uses is a
two-pole Butterworth filter and worked much better! I used “sox -v 20
SAQ122421.wav SAQ122421_20Hz.wav bandpass 493 20” and encoded to mp3. The
file can be downloaded at

vlfrx-tools has a a few spectrum analyzing utilities and I was able to look
at the non-coherent spectrum integrated over the duration of the
transmission. It generated a plot with a little peak about 3 magnitudes
above the noise floor. Plot below:

I compared it to another plot created by Paul that shows a similar peak at
the same frequency. My spectrum plot is attached showing the peak of SAQ’s
carrier. To generate the plot: vtread -T 2021-12-24_07:46:00,+16m
/data/vlf_96k > SAQ122421_96k_spec.vt and plotted 1:2 in gnuplot.

Thank you again for your confirmation!!


On 12/24/21, John Magliacane <kd2bd at yahoo.com> wrote:
>  Jonathan,
> I have made several attempts to copy SAQ in the past from New Jersey over
> the years, but the best I could do was see a weak trace buried under the
> noise using "baudline" spectrum analysis software. Still, this was enough
> earn several QSL cards. :-)
> I used baudline on your recording and could see a trace of SAQ at around
> Hz, in between a lot of powerline harmonics spaced every 120 Hz.
> Based on that success, I performed some additional bandpass filtering
> the "play" feature of SoX, and I could clearly hear CW about 2 minutes
> the recording! (VVV DE SAQ). I used a 20 Hz bandpass filter centered on
> Hz (play -v 20 SAQ122421.mp3 bandpass 493 20).
> You did it! Congratulations!
> 73 de John, KD2BD
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