[TangerineSDR] SAQ scheduled to air on World Radio Day Feb 13th, 2023

Jonathan emuman100 at gmail.com
Sun Feb 19 13:29:27 EST 2023

Hi All,

I wanted to share my 02/13/2023 SAQ transmission report.

Using vtsid, I set it up to record the amplitude of SAQ just to see if I
could see any possible signal from the 1500UT transmission. This looks
[image: Screen Shot 2023-02-13 at 9.21.18 PM.png]

While a lot of it looks pretty noisy, it looks like there was some signal
around the time of the transmission at 1500UT. Zooming in looks even more
[image: Screen Shot 2023-02-13 at 9.21.48 PM.png]

It could just be noise peaks, but their duration seemed too long for noise,
so I was hopeful! To be sure, I wanted to look at the non-coherent
spectrum. Using vlfrx-tools, I used this signal pipeline from the raw data
I pulled from the signal store and ran it through vtnspec, integrating over
the transmission duration:

vtcat -T2023-02-13_14:49,+12m 2023-02-13_14-00p1.5h_SAQ_test_and_main.vt |
vtnspec -f17200 -w200 -r1 -av > SAQ220213.dat

I used vtcat to send only the transmission duration to the input of vtnspec
with a center frequency of 17200 Hz, 200 Hz wide, at a resolution of 1 Hz.
Using gnuplot, I plotted SAQ220213.dat using the following script:

echo "set terminal png small
         set style data lines
         set xlabel 'Frequency, Hz'
         set ylabel 'Relative amplitude'
         set nokey
         set title '2021-12-24_07:46:00,+16m in 1Hz'
         plot 'SAQ122421.dat' using 1:2
     " | gnuplot > SAQ122421.png

This produced the following plot:
[image: SAQ230213.png]

Peaking only a little bit above the noise a very promising peak of SAQ's
signal! Compared to Christmas Eve of 2021, this is much more centered at
17.2 kHz. Well done getting such an old transmitter as spot on as this
transmission is! Here is vtnspec's output:

vtnspec: amplitudes 0 m/p/r: 4.557e-06 6.411e-06 1.407 p-m 5.01 sigma

Now, the real test is the listening test. Using the following pipeline, I
produced a wav file from the data, running it through some filtering:

vtcat -T2023-02-13_14:49,+12m 2023-02-13_14-00p1.5h_SAQ_test_and_main.vt |
vtfilter -h bp,f=17200,w=1000 -g100 | vtmult -f 16700 | vtmix -c 1,-j |
vtraw -ow > SAQ230213.wav

Again, vtcat pulls the duration of the transmission and runs it through
vtfilter at the 17200 Hz center frequency, 1000 Hz wide, adding a gain of
100. It's then sent to vtmult and vtmix to downmix down to 500 Hz, then
converted to wav. I used lame to convert it to mp3:

lame -b64 -m m SAQ230213.wav SAQ230213.mp3

You can listen to it here

Since the signal was pretty close to the noise floor, it blends in with the
noise pretty well, but if you listen very carefully, you can hear the
message!! Using smaller bandwidths didn't give me the desired tone due to
the fact the filter is a brick wall filter, so I decided to use the
Butterworth bandpass filter in sox, 20 Hz wide center at 500 Hz, also
adding a gain of 20 to make it even more audible:

sox -v 20 SAQ230213.wav SAQ230213_20Hz_g20.wav bandpass 500 20

Encoding to mp3 again using lame:

lame -b64 -m m SAQ230213_20Hz_g20.wav SAQ230213_20Hz_g20.mp3

You can listen to it here
It's much easier on the ears this time and makes copying the message much
easier. There was much less fading this time, but possibly due to the fact
that the transmission occurred during local daytime. It's really cool that
signal processing can bring this transmission out of the noise! A huge
thanks to Paul for helping me with this last year and for his vlfrx-tools

Can anyone copy the message from my audio file and decode it? If you can,
please post it to this thread.



On Mon, Feb 13, 2023 at 12:21 PM Joe Hobart <nova at npgcable.com> wrote:

> Hi Jonathan,
> Nothing heard here or seen on WF at or around 17.2 kHz from 1200 to 1530
> UTC.
> Plenty of other signals present.  Due to distance and time of day, the
> non-detection of SAQ was considered likely.
> Good copy from youtube.
> Here is a screen grab typical of the listening period showing at least 4
> Navy
> transmitters and other signals.  The carrier at 15 kHz is a locally
> generated
> weak signal.  The intermittent carrier at 18 kHz is unknown.
> 73,
> Joe, W7LUX
> Flagstaff, AZ
> On 2/13/2023 8:11 AM, Jonathan via TangerineSDR wrote:
> > Hi All,
> >
> > Reminder, the SAQ transmission is currently going on. (15:00UT)
> >
> > Jonathan
> > KC3EEY
> >
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus
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