Hi ULF,
Now the results of the post-processing of my 3 day recording are
available. It shows very clearly that my 250 nW ERP (average 46 mA
antenna current), 2970 Hz signal was copied in 31.3 km
distance. The recording location was in a more or less quiet location,
in http://no.nonsense.ee/qth/map.html?qth=JN49IQ37AM. The transmission
path is shown in http://no.nonsense.ee/qth/map.html?qth=JN49IQ37AM&from=jn49ik00wd
In this second attempt, everything worked fine, stable GPS reception,
accurate orientation of the vertical, single turn receive loop and the
recording of a single 30 GB .raw file at 32 kS/s (covering 0...16 kHz).
However the QRN could have been lower. But there was no QRM by
electrical fences...
Here's a spectrogram showing the complete, unfiltered recording: https://dl.dropboxusercontent.com/u/19882028/ULF/31km_wide_3days.jpg
Of course there is nothing visible of the transmission in this
resolution, it is just an overview to get an impression about QRN and
QRM in that location. QRM from trains and mains harmonics is the
critical parameter on ULF.
The transmission consists of 3 parts: A long dash on 2970.000 Hz, then
the message "73" in DFCW-12000 (2.5 mHz frequency shift) with the lower
dash sent on 2970.000 Hz and then another long dash on 2969.990 Hz
After filtering and noise blanking, here are the resulting spectrograms
in 476 uHz and 238 uHz:
https://dl.dropboxusercontent.com/u/19882028/ULF/31km_476uHz.jpg
https://dl.dropboxusercontent.com/u/19882028/ULF/31km_238uHz.jpg
The experienced visual human spectrogram interpreter experts may find a
significant part of the message :-)
Just as a reference, here are spectrograms showing the same
transmission received in 3.5 km distance
(http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html).
https://dl.dropboxusercontent.com/u/19882028/ULF/ref_424uHz.jpg
https://dl.dropboxusercontent.com/u/19882028/ULF/ref_212uHz.jpg
I'm not sure if this is the highest distance ever crossed with a
message by radio amateurs on ULF (0.3...3 kHz), but it is certainly one
of them :-)
A new experiment in about 65 km distance is in preparation. Probably it
will be done in a few weeks. The location will be quieter (the Pfälzer
Wald, JN39VH) and there will be less QRN!
73, Stefan/DK7FC
Am 11.09.2016 16:35, schrieb DK7FC:
Hi ULF,
Since yesterday (10.Sep), 11 UTC, i'm running a new experiment on the
101 km band. It is in 31.2 km distance to my transmitter-site.
The last experiment did not produce satisfying results due to various
reasons.
Now i improved the loop cross section area, the loop orientation, GPS
reception (for the 1 PPS + NMEA reference signal). Furthermore the
recording sample rate was reduced to 32 kS/s which allows about 3 days
of stereo recording.
I'm still using the Raspberry Pi2 for therecording. The system consumes
just 150 mA from a 12V battery. 3x 7 Ah lead acid batteries are in use
now.
The transmission contains stable carriers and a short DFCW-12000
message, "73". The transmission can be followed on my 3.5 km distant
forest grabber at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html ,
as usual.
Relative to the last experiment, the average QRN has dropped
significantly now, another advantage. So i'm quite optimistic to get a
good result!
The next experiment in about 60 km distance is already in preparation.
Then i will use my new coil which is still in preparation. The last
measurement, after completing the 3rd stack, showed a resonance
frequency of 4.27 kHz. So it should have 2.8 H now...
In the next experiment, i will use 100 mA antenna current, again a
about 6 dB stronger signal.
The current experiment will stop on Tuesday afternoon. Results can be
expected in the end of the next week.
73, Stefan/DK7FC
|
|
