[TangerineSDR] Merry Christmas! SAQ Grimeton Christmas Eve Transmission

[Jonathan]

Merry Christmas All!

SAQ at Grimeton, Sweden transmitted their annual Christmas Eve message
on 17.2 kHz CW using the Alexanderson alternator.

Recently, Nathaniel and I finished installing conduit and cable for a
VLF SDR and the PSWS ground magnetometer. We installed the VLF SDR and
active VLF antenna as well as the ground magnetometer and got both up
and running.

For many years, I wanted to be able to receive the SAQ Christmas Eve
transmission, but here in the US, it can be difficult. The
transmission was scheduled to occur at around 3AM EST or 8 UT. My VLF
SDR was recording the VLF band this snowy morning and captured the
spectrum. Unfortunately, the propagation conditions weren't the best,
but I was able to hear it, but just barely, and I mean just barely!
Here is a link to the mp3 file:
https://drive.google.com/file/d/1DhiKg9azAJzBZkv6rqFCXZQh1VZnhiSy/view?usp=sharing

Only at 14:40 into the recording can you just barely make out the 500
Hz downmixed carrier. I can maybe copy a few characters. If anyone is
interested how I created the file, here is a long pipe using
vlfrx-tools to read data from the data store, bandpass filter at 17.2
kHz center with 1 kHz bandwidth. Comments are added for description:

vtread -T 2021-12-24_07:41:30,+24m /data/vlf_96k | # read from data
store starting at 12/24/2021 7:41:30 UT for a duration of 24 minutes.
   vtfilter -h bp,f=17200,w=1000 -g50 | # Insert a bandpass filter
with fc=17200 Hz, 1000 Hz wide with a gain of 50.
   vtmult -f 16700 | # downmix carrier to 500 Hz using 16700 Hz local oscillator
   vtmix -c 1,-j | # select the upper sideband
   vtraw -ow | # convert to wav
lame -b64 -m m - SAQ122421.mp3 # encode pipe output to mp3

All is not entirely lost. The author of vlfrx-tools was able to
capture it at his location in the UK. Here is a link to his recording
where the whole message can be copied. At the very beginning of the
recording, there is a test transmission. Here is the link:
https://drive.google.com/file/d/1ruY291-G4sKk4DKJMUmTkSJaFjcvrkUC/view?usp=sharing

Credit to the author of vlfrx-tools for assistance on extracting the
recording and processing it. Much gratitude to Paul, the author of
vlfrx-tools, for his help, expertise, patience, and guidance
throughout the years and now, as well as his software and
documentation. Much gratitude to Nathaniel as well. For a recorded
live stream at SAQ in Grimeton and more information about the
transmitter, please see the Alexander Association's web site:
https://alexander.n.se/en/

Jonathan
KC3EEY