Hello,
I'm posting the description of the decode, people which use the linux
software will find it obvious, but maybe someone will find it
interesting/helpful for his attemps. BTW I got Stefan's permission to
disclose the message to the mailing list.
The message didn't decode correctly at first with the noiseblanker
settings i've used (-a2 -d0 -t 10). Tried the -f9 option:
$ vtraw -oa < resampled_file | ./ebnaut -d -N7 -p 16K21A -S 24 -k 5 -r240 -c2 -PS -v
-L 20000 2>&1 |tee decwy
However with only 5 bits of crc there are many valid decodes:
$ grep found decwy |cut -d \[ -f 2 |cut -d \] -f 1 |sort -u | wc -l
67495
67495 of unique decodes is not good, we can't sift through this manually
and it will have a lot of valid looking messages.
Lets cheat a bit: Paul wrote that it is a famous name, so we can
hypothesize that it will be only letters:
$ grep found decwy |cut -d \[ -f 2 |cut -d \] -f 1 |sort -u |egrep '^[A-Z]+$'
|wc -l
352
352 is much better, i can look through all of the messages manually:
$ grep found decwy |cut -d \[ -f 2 |cut -d \] -f 1 |sort -u |egrep '^[A-Z]+$' |
less
And the only message which makes sense is MARCONI :)
I dug out the best message from the ebnaut decoder logs:
found rank 13961 ber 4.0858e-01 Eb/N0 -1.4 M -8.404992819e-01 [MARCONI] ps[ 83
-90 -60 -90 -60]
carrier phase: 5.1 deg
carrier Eb/N0: -4.1 dB
carrier Es/N0: -18.44 dB
carrier S/N: 11.87 dB in 38.9 uHz, -32.24 dB in 1Hz, -66.22 dB in 2.5kHz
elapsed 1334
Now let's try to find the best noiseblanker settings:
PLIK2=plik_dk7fc_20170603_1_raw1
FREQ=6470.1
TT=2017-06-03_03:00:00,+25728
vtread -T$TT /mnt/rawvlf | vtfilter -h bp,f=${FREQ},w=3000 > $PLIK2
for a in 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6
do
for t in 10 100
do
echo a=$a t=$t
vtblank -v -a$a -d0 -t$t < $PLIK2 | \
vtmult -f ${FREQ} | \
vtresample -r 240 > ${PLIK2}_${a}_${t}
done
done
This will create files called plik_dk7fc_20170603_1_raw1_XX_YY (where XX
is the -a vtblank setting and YY is the -t setting).
Lets go through the files and see how they match our hypothesis:
$ for i in plik_dk7fc_20170603_1_raw1_*; do echo $i; vtraw -oa < $i |
./ebnaut -d -N7 -p 16K21A -S 24 -k 5 -r240 -c2 -PS -v -L 20000 -f15 -f16 -M
MARCONI; echo; done
... after a lot of output this one looks best:
plik_dk7fc_20170603_1_raw1_1.4_100
padded 0.267 seconds at end
initial reference phase -0.2 amplitude 2.277e-02
carrier phase: 2.4
carrier Eb/N0: -2.7 dB
carrier S/N: 13.28 dB in 38.9 uHz
Let's try to decode the plik_dk7fc_20170603_1_raw1_1.4_100 file without
the -f9 option and see how that works:
$ vtraw -oa < plik_dk7fc_20170603_1_raw1_1.4_100 | ./ebnaut -d -N7 -p 16K21A
-S 24 -k 5 -r240 -c2 -PS -v -L 200000
padded 0.267 seconds at end
initial reference phase -0.2 amplitude 2.277e-02
prep [ 0 0 0 0 0]
found rank 141 ber 4.1884e-01 Eb/N0 -2.4 M -6.664184332e-01 [MARCONI] ps [ 0
0 0 0 0]
carrier phase: 2.6 deg
carrier Eb/N0: -2.7 dB
carrier Es/N0: -17.02 dB
carrier S/N: 13.28 dB in 38.9 uHz, -30.82 dB in 1Hz, -64.80 dB in 2.5kHz
elapsed 42
Yes, it works. Turns out that the best vtblank settings for this
transmission were -a1.4 -d0 -t100.
VY 73
Jacek / SQ5BPF
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