--
Please follow the HamSCI Community Participation Guidelines at http://hamsci.org/hamsci-community-participation-guidelines.
---
You received this message because you are subscribed to the Google Groups "HamSCI" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hamsci+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/CAOY0kB2Gq-vnGgsV%3DFRiV%2BrSspTgEpc_wDPbRUUmyBns0SofQQ%40mail.gmail.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/CA%2BK5gzd9a1kSEeP5V23ZkRJxnvWVDT2LT5Fq19FVcKqkmRqtGA%40mail.gmail.com.
That is wonderful news, Jonathan! Congratulations!
73 Nathaniel W2NAF
From: ham...@googlegroups.com <ham...@googlegroups.com>
On Behalf Of Jonathan
Sent: Wednesday, January 18, 2023 12:57 PM
To: TangerineSDR Listserv <tanger...@lists.tapr.org>; Unknown <ham...@googlegroups.com>
Subject: [HamSCI] First Amateur VLF Transmission Detected at the W2NAF-KC3EEY VLF Receiver!
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.
It also was detected at a VLF receiver at Forest, Virginia as well:
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:
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.
Jonathan
KC3EEY
--
To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/PH0PR03MB70176245EF58BFB49191EDCCF2C79%40PH0PR03MB7017.namprd03.prod.outlook.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/d5f88601-08d6-bf92-d000-389acc424a1a%40gmail.com.