Congratulations Stefan!
Excellent work in all respects,
73,
Jim AA5BW
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
