[TangerineSDR] [HamSCI] First Amateur VLF Transmission Detected at the W2NAF-KC3EEY VLF Receiver!

Robert McGwier rwmcgwier at gmail.com
Wed Jan 18 14:33:50 EST 2023 

Congratulations!

Bob N4HY


On Wed, Jan 18, 2023 at 12:57 PM Jonathan <emuman100 at gmail.com> wrote:

> A new first for the W2NAF-KC3EEY VLF receiver! Ameteur transmissions from
> VLF Radio Amateur DL3JMM in Germany have been detected at the receiver and
> messages have been decoded! DL3JMM's QTH is over 6500km away from
> Springbrook and consists of both a land and sea propagation path. The
> message was encoded using EbNaut, 8k19a polynomial coding, 16-bit crc, 5
> characters message length with a 30 second symbol period at a frequency of
> 8270.03Hz. This information is important to configure the decoder. The
> carrier's spectral peak can be seen on this spectrum plot integrated over
> the transmission period. It was generated on Paul's server from the
> uplinked vorbis encoded audio stream of VLF spectrum data.
> [image: Screen Shot 2023-01-15 at 1.49.00 AM.png]
>
> It also was detected at a VLF receiver at Forest, Virginia as well:
> [image: Screen Shot 2023-01-15 at 1.50.03 AM.png]
>
> I then pulled the spectrum data from the raw downsampled and hum filtered
> data and integrated over the length of the transmission. To do this, here
> is the vlfrx-tools signal processing chain. First, the spectrum is fed
> through a 3 kHz wide brick wall filter with a center frequency of 8270 kHz.
> Then, it's fed through a sferic blanker to blank out sferics based on a
> setting that produced the lowest noise floor. Finally, it's fed into the
> narroband spectrum analyzer with 53.07uHz resolution.
>
> vtfilter -h bp,f=8270,w=3000
> 2023-01-13_04-15-00_18900s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-18840s_high_power.vt
> | vtblank -a12 -d0 -t100 -v | vtnspec -v -r53.07e-6 -w0.01 -f8270.03 >
> "2023-01-13_04-15-00_18900s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-18840s_high_power.dat"
>
> It produced a narrowband spectrum with a carrier peak of 5.622e-08:
> vtnspec: amplitudes 0 m/p/r: 1.203e-08 5.622e-08 4.672 p-m 6.61 sigma
>
> The output data was plotted in gnuplot, also showing the carrier's peak:
> [image:
> 2023-01-13_04-15-00_18900s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-18840s_high_power_a12.png]
>
> To see if I could get a decode, I ran it through the ebnaut decoder using
> the following vlfrx-tools processing chain. After the sferic blanker, the
> spectrum is fed into a multiplicative mixer at the carrier frequency to
> produce baseband IQ data. The output of the mixer is then downsampled and
> converted to ascii data, then sent to the ebnaut decoder with the encoding
> parameters of the message. -c2 tells the encoder to use both processor
> cores.
>
> vtfilter -h bp,f=8270.03,w=3000
> 2023-01-13_04-15-00_18900s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-18840s_high_power.vt
> | vtblank -a12 -d0 -t100 -v | vtmult -f 8270.03 | vtresample -r 240 |
> vtresample -r 1 | vtraw -oa | ebnaut -d -N5 -p 8K19A -S30 -k16 -r1 -c2 -v
> -L20000 -PS -T60
>
> But this did not result in a successful decode. A few more dB was needed.
> Thankfully, DL3JMM did more transmissions in his transmission campaign at
> the following times, he wrote:
>
> The next transmission already started at 18:00 UTC because 18 is modulo of
> 6h. So they begin
> next broadcasts probably:
>
> today (01.14):
>
> - 18:00
>
> tomorrow (01.15):
>
> - 00:00
> - 06:00
> - 12:00
> - 18:00
>
> Monday (01.16):
>
> - 00:00
> - 06:00
>
> Here is a spectrogram showing the transmissions. Between transmissions,
> only an unmodulated carrier.
> [image: image.png]
> You can see the first transmission on the 13th, one on the 14th, four on
> the 15th, and the beginning of the one on the 16th.
>
> Paul was able to achieve a decode at Forest, VA for the midnight
> transmission on the 16th, however, I still needed a few more dBs for that
> transmission and recommended I stack both midnight transmissions. Stacking
> feeds both transmissions through an additive mixer and aligns timestamps
> and sampling. This allows the signal power from both transmissions to
> add and will increase the likelihood of a decode. First, I converted both
> midnight transmissions to baseband IQ data using the following vlfrx-tools
> signal processing chains:
>
> vtfilter -h bp,f=8270,w=3000
> 2023-01-14_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1.vt |
> vtblank -a12 -d0 -t200 -v | vtmult -f 8270.03 | vtresample -r 240 |
> vtresample -r 1 >
> 2023-01-14_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
>
> vtfilter -h bp,f=8270,w=3000
> 2023-01-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1.vt |
> vtblank -a12 -d0 -t200 -v | vtmult -f 8270.03 | vtresample -r 240 |
> vtresample -r 1 >
> 2023-01-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
>
> Then, I fed both into the stacking script:
>
> bash stack2
> 2023-01-14_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
> 2023-01-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
> >
> 2023-01-14-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband_stacked.vt
> 2023-01-14_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
> 1673740200.000000 3.914e+05 1.532e+11
> 2023-01-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband.vt
> 1673826600.000000 5.056e+05 2.556e+11
>
> Finally, I converted the stacked transmissions to ascii and fed it into
> the decoder. I GOT A SUCCESSFUL DECODE! The message is in brackets with an
> Eb/N0 of 2.5dB!!
>
> vtcat -S600
> 2023-01-14-15_23-50_16000s_DL3JMM_8270.03_8K19A-crc16-30s-5chars-16000s_1_r1_baseband_stacked.vt
> | vtraw -oa | ebnaut -dp8K19A -r1 -S30 -N5 -c2 -PU -L50000 -v
> initial reference phase -48.3 amplitude 2.244e+01
> phase   0    0    0    0    0
> found rank 0 ber 3.5156e-01 Eb/N0 1.2 M -8.639339600e+02 ph 0 0,0,0,0
> [BERND]
> carrier phase: -11.9 deg
> carrier amplitude: 5.749e-02
> carrier Eb/N0: 2.5 dB
> carrier Es/N0: -10.05 dB
> carrier S/N: 17.04 dB in 65.1 uHz, -24.83 dB in 1Hz, -58.81 dB in 2.5kHz
> elapsed 2
> phase   1  180  180  180  180
> phase   2   30   30   30   30
> phase   3 -150 -150 -150 -150
> phase   4  -30  -30  -30  -30
> phase   5  150  150  150  150
> phase   6   60   60   60   60
> phase   7 -120 -120 -120 -120
> phase   8  -60  -60  -60  -60
> phase   9  120  120  120  120
> phase  10   90   90   90   90
> phase  11  -90  -90  -90  -90
> vstack: max height 15
>
> I also wanted to mention the CPU usage during the decode. EbNaut uses
> powerful error correction and processing for message decodes. CPU usage for
> the decoder process was 130%, meaning one core was completely utilized and
> the other was 30% utilized!! Paul mentioned that this is the only amateur
> radio mode that uses more power to decode the message than it does to
> transmit the message!
>
> Congratulations to Paul and Bernd DL3JMM on a successful transmission
> campaign and a first for the W2NAF-KC3EEY VLF Receiver!!
>
> More about the EbNaut mode can be found here <http://abelian.org/ebnaut/>.
>
> Jonathan
> KC3EEY
>
>
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> .
>


-- 
Dr. Robert W McGwier, Ph.D.
Adjunct Faculty, Virginia Tech
Affiliated Faculty, University of Scranton
ARDC Member of Board
N4HY: ARRL, TAPR, AMSAT, EARC, CSVHFS
Sky: AAVSO, Sky360, explorescu.org, Skyscrapers
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