Hello
Stefan,
Congratulations
on your 40.5 km 970 Hz record with loop-only receiver; and the
successful preparation that preceded.
Do
you think that you might have also overcome a receiver polarization
challenge in the process?
With
a surface TX loop to RX loop near field link I keep both loop planes
vertical (both loop axes horizontal), with the RX loop axis pointing at
the transmitter (RX loop plane facing the transmitter).
With
a surface TX loop to RX loop far field link I keep both loop planes
vertical (both loop axes horizontal), with the RX loop axis pointing
perpendicular to the transmitter (RX loop plane edge pointing toward
the transmitter).
With
a TX vertical-antenna to RX loop far field link I keep the RX loop axis
pointing perpendicular to the transmitter (RX loop plane edge pointing
toward the transmitter).
I’m
not sure what the polarization of your TX antenna would be at 40.5 km
(~ 1/8 wavelength, near the first of the two near/far-boundary
impedance intersections), or what the best RX loop orientation would be
for such TX near-field-boundary signal polarization. Do you think that
your RX loop was fairly well aligned for the 970 Hz 1/8 wavelength
polarization of your TX signal?
Congratulations
on another important and most interesting (970 Hz near-far
impedance-crossover point) record!
73,
Jim
AA5BW
Hello ULF friends,
Here is the summary of my recent portable experiment on 970.005 Hz.
The goal of the experiment was to undoubtly detect my own transmission
in a distance of 40.5 km. The experiment took about 8 days, starting
30.JAN.2018, 16:30 UTC. For the first 3 days, a carrier was transmitted
on 970.005 Hz, for 48 hours, and then 24 hours on 970.0025 Hz.
Afterwards, a 2 character EbNaut message was transmitted, taking 24
hours exactly, two times repeated. And finally, a 5 character message
was transmitted, also taking 24 hours, two times repeated.
This is the path http://k7fry.com/grid/?qth=JN49BK33UG&from=jn49ik00wd
which the 18 nW ERP signal had to cross.
Along with the other experiments i've done during that time, it took
nearly two months for me to learn how to operate Paul's vlfrx tools and
to do all the post processing.
I had to determine:
-The best noise blanker settings,
-The best filter shape, bandwidth and center frequency
-The optimum hum filter parameter settings
-The phase between E field (whip) and H field (loop)
-The best mixing coefficients (amplitude, phase) between E and H
-The phase difference of the signal between day and night
...all to maximise the SNR of the carrier peak and Eb/N0 of the
messages.
Unfortunately the E field was not usable for most of the days. Either
something got damaged on the front end JFET or the shielding effect of
sourrounding trees has been much higher than expected. The performance
of the 84 turn loop antenna having 0.8 m diameter and a low noise
preamp was fine, though not optimal since there were AM broadcast
signals audible during the sunrise and sunset (a resonance on HF,
resulting in an overloaded preamp at times?!).
So all in all there were a lot of performace limiting issues.
Anyway, the two character message was decoded without much tweaking of
blanker etc. settings. Based on these signals to analyse, along with
the carrier, it was possible to find the best settings to even get a
decode of the 5 character message in the end! The carrier result and
the 5 character message is H field only!
Here are the results:
Spectrum peak of the 72 hour carrier transmission, combined in
one peak: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/TR3_Endversion.png
2 character message: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/2ch970Hz40km_E+H.png
5 character message: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/5ch970Hz40km.png
So let me conclude the experiment was a full success, despite all the
trouble and limitations i had. And it means that more distance can be
expected if the RX system is working as intended!
This new distance record of 40.5 km on the 309 km band is still in the
near field for that wave! See http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/Nahfeld%C3%BCbergang.png
These are the locations of all experiments done on the 309 km band so
far: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/970Hz_bisher.png
For the next experiment, i definitively plan to cross the far field
border ( > 49.3 km). The idea is to use about 3 dB more power and a
working RX system and a better location for the E field :-) When doing
it in the summer months, the 3 dB more power will be compensated by QRN
i fear.
A photo from the RX site in the snow: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/RX_site.jpg
A photo showing the data recorder: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/Raspi.jpg
And the batteries afterwards: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/40km/Batt.jpg
73, Stefan
PS: Thanks to Paul Nicholson for the support in learning how to use
vlfrx tools!
Am 08.02.2018 13:44, schrieb DK7FC:
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
