Hello dear friends of the Ultra Low Frequencies,
Update:
There are a few things to note so far:
I made a mistake in the calculation of the ERP. It is not 10 nW
but rather 18 nW.
All transmissions seemed to go out as intended. The stream from the
local tree was interrupted almost daily due to lack of solar energy but
at least a few hours came through. From these few hours i got decodes
of each carrier transmissions. I also got decodes of all EbNaut
messages. So things went well from the TX site it seems.
The 36 mA antenna current (12 kV antenna voltage) was running
for 8 days without a single interruption. The constructed resonating
transformer has done its job flawlessly.
Since i decided to take back the RX equipment on the 7th of February,
there was some more time for another EbNaut message:
06.Feb, 17:30 UTC: EbNaut, 16K21A, 1 char, 90 sec, CRC27 (21:12:00)
The experiment stopped at 15:45 UTC. BTW the exact location was JN49BK33UG That is a
distance of 40.5 km to the TX site. But so far there are no decodes or
traces, so no success so far.
The next good step is that the whole RX equipment has still been in its
place, nothing stolen, nothing damaged. The Raspi was still running
after 8 days. The Raspi was supplied by two 12 V / 26 Ah lead gel
accus. They were standing in the snow and discharged to 11.8 V! The two
accus for the preamps of the loop and vertical were still above 12.3 V.
So that was all fine too!
Now the stuff is sorted, cleaned and the accus are charging and warming
up again here.
I just started the Raspi and checked the data on the 64 GB USB stick.
This looks good and promising, see attachment. And it looks like there
were no timing breaks of the GPS module.
For the first time i run the recording using vlfrx tooly by Paul and
the octo soundcard. Also it is the first set of data i have available
to build a cardioid antenna by software... Exciting stuff.
The recording process by vlfrx tools saves to a new file each day.
Here the files are 7.8 GB large: 2 channels * 24000
samples/(channel*second) * 16 bit/sample * 3600 seconds/hour * 24
hours/day * 1/8 Byte/bit * 1/1024 kByte/Byte * 1/1024 MBity/kByte *
1/1024 GByte/MByte = 7.72 GB/day
Obviously the recording process was stopped during the last night 03:58
UTC because the USB stick capacity seems to be just 58 GB actually. The
recording is started/stopped by switching a switch which is connected
to one of the GPIO pins. This is necessary because in the field there
is no monitor and no keyboard of course. At start-up, a scripts is
executed which checks the logic level of the pin where the switch is
connected... During the recording process, a loop is running within
this script which periodically checks the remaining available
space of the data carrier. As soon as the remaining space becomes less
than 100 kB, the recording process is stopped. This ensures that there
is still enough space to save the log files which are written at the
end of the recording process. It also ensures that there are no crashes
and unwanted data loss, broken files etc...
In a few days i can report about the results, so stay tuned...
73, Stefan
Am 31.01.2018 14:30, schrieb DK7FC:
Hi all,
Since yesterday, ~ 17 UTC, i'm running a new portable experiment on 970
Hz, or the 309 km band. The receiver site is somewhere in the forest in
JN49BK,
a distance of
40 km to the TX site.
I carried a lot of accus to that location and the USB stick where the
data is written on has 64 GB, so i can run the experiment for more than
one week! :-)
For the first time i'm using two antennas. An active E field antenna
with a 1.5 m long steel wire as the capacitive probe. It is mounted on
a 10 m high pole. The E field preamp is supplied by a separate battery
and uses an isolation transformer with a low pass filter applied.
The second antenna is my compact loop with 80 cm diameter and 84 turns.
It uses a low noise preamp (also supplied by a separate battery) using
a LT1028. This loop RX worked surprisingly well on 4470 Hz when beeing
in France last September. Hopefully it will pick up the signal.
Unfortunately the E field antenna is not very high above the
sourrounding trees, so the sensitivity may be limited. Also the H field
antenna showed much more mains hum than expected in this location. So
it may be a bit questionable if the experiment will be successful. The
long transmissions will allow to stack carrier transmissions and/or
EbNaut transmissions though...
Running 36 mA antenna current means an ERP of 10 nW on that
frequency.
My transmission plan is:
30.JAN, 17 UTC: Carrier on 970.005 Hz
01.Feb, 17 UTC: Carrier on 970.0025 Hz
02.Feb, 17 UTC: EbNaut, 16K21A, 2 char, 100 sec, CRC22 (24 hours)
03.Feb, 17 UTC: EbNaut, 16K21A, 2 char, 100 sec, CRC22 (24 hours)
04.Feb, 17 UTC: EbNaut, 16K21A, 5 char, 80 sec, CRC17 (23:49:20)
05.Feb, 17 UTC: EbNaut, 16K21A, 5 char, 80 sec, CRC17 (23:49:20)
Not sure if someone else can pick up the signal. Most likely not. But
new components to rise the voltage to 20 kV in a next experiment are
already in preparation...
73, Stefan
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