Fantastic work, Stefan!
John
73 de VA3VVV
Toronto, Canada
--------------------------------------------
On Thu, 6/15/17, DK7FC <[email protected]> wrote:
Subject: Re: ULF: New experiment on 970 Hz, results (3/3)
To: "[email protected]" <[email protected]>, "Renato
Romero" <[email protected]>
Received: Thursday, June 15, 2017, 7:02 PM
Hello dear ULF friends,
Here is my summary of the latest experiment on ULF
which took
place from 16...20 of May 2017. The experiment was to
transmit
for 90 hours on near 970 Hz, a wavelength of
309 km.
The transmitter site was my normal inv-L antenna, 30m above
ground,
about 70m long. A modified HV mains transformer, driven by a
homemade
linear mode class-AB PA, produced 5 kV on the antenna
wire.
This results in 15 mA antenna current and an ERP of about
3 nW.
The signals were generated by SpectrumLab software. The
transmit signal
was locked to a GPS reference.
The receiver position was in JN49LN91GB, that's a
distance
of 27.2 km to the transmitter site. This is the path
between TX and
RX: http://no.nonsense.ee/qth/map.html?qth=JN49LN91GB&from=jn49ik00wd
This time, an active E field antenna was used for reception
because
27.2 km distance is still in the near field for that
wavelength! It is about 55 % of the far field border
distance.
The signal was recorded by a Raspberry Pi running a USB
stereo
soundcard. The second channel was recording a reference
signal
containing PPS pulses and NMEA data from a NEO-6M GPS-module
for
compensating sample rate drift and sample losses. The data
was written
into a ~ 30 GB file on an USB stick connected to the
Raspi.
The data was post processed afterwards. Spectrograms in
bandwidths of
424 uHz, 212 uHz, 106 uHz and 47 uHz were generated. A few
optimisations were done to find suitable settings for a band
pass
filter and noise blanker.
The first time, two EbNaut messages were transmitted, see
the
transmission plan:
May, 16th:
14:43:08 UTC: Start of recording. Carrier on 970.005 Hz for
the rest of
the day.
May, 17th:
Continuing of the carrier transmission, for the whole
day.
May, 18th:
00:00:00 UTC: EbNaut, 5 characters, 16K21A, CRC4, 100 second
symbols.
Taking 24 hours exactly. The message was
"DK7FC"
May, 19th:
00:00:00 UTC: Carrier on 970.01 Hz, for the whole day.
May, 20th:
00:00:00 UTC: EbNaut, 2 characters, 16K21A, CRC3, 60 second
symbols.
The message was "73".
09:20:00 UTC: End of EbNaut transmission.
10:27:05 UTC: End of recording.
Here are all spectrograms and images:
https://www.dropbox.com/sh/n7k0il4pp6vqbbc/AACbfwbN4TQ1RrS6YIEDYzMpa?dl=0
The signal shows up to 15 dB in 47 uHz. There is no
QRM in +-
10 Hz but the QRN was extreme, including local thunderstorms
on the
19th. Several times there were lost samples into the
recording but
SpecLab corrected that nicely, so the spectrograms look as
expected.
Fortunately both EbNaut messages were decoded after a
longer
series of decode attempts. So there can be no doubt that
this was a
successful experiment.
The next attempt will be to reach the far field border
distance in >
49.3 km. I will need about 10 dB more radiated power, which
is possible
with some effort. Maybe an improvement on the receiver site
will help
to rise the SNR a bit more!
73, Stefan/DK7FC
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