Please let me know dates/times/frequencies/modes if you plan any VLF tests so I can publish information here. As I don't always get told of tests and am sometimes away and unable to update news, please check the RSGB's LF Reflector email list or the Sub 9kHz Amateur Radio Yahoo group for late news of tests.
Dec 10th 2015
Uwe DJ8WX has been testing recently on 8270Hz.
Nov 10th 2015
Joe VO1NA has been tinkering on VLF and has copied his signal at 5km. Paul Nicholson thinks a stable VLF signal of 20uW would be detected by him in the UK. The key is stability so narrow RX bandwidths can be used.
Oct 24th 2015
Marco Maiello IU7EDU has a new grabber on 8270Hz. See iu7edu.jimdo.com
Sept 8th 2015
RN3AUS has been doing experiments at ELF/ULF. See his website.
http://rn3aus.narod.ru/elf/elf.html
July 22nd 2015
Stefan DK7FC is getting closer to doing a tweek resonance RX test. He reports:
"Hi VLF,
Now I continued with measurements of the new loop. I took 3 different capacitors in series and searched for the maximum antenna current for a fundamental frequency. I had and have no idea about the L of that loop.
Measurement: https://dl.dropboxusercontent.com/u/19882028/VLF/20150721_225451.jpg
C = 100 nF in series => f(res) = 42.1 kHz
C = 1 uF => 12.35 kHz
C = 4 uF => 5.48 kHz (not a sharp resonance peak)
Hmm, the VFO has a sine output so i assume the measurement should be accurate, reasonably. Currents have been in the range of 50...70 mA. I need to repeat the tests with more power and an analog RF current measurement. This could be done tomorrow.
Actually f(res, 1uF) should be f(res, 100nF)/3.16 but it isn't! The factor is 3.4. Maybe this has to do with ground conductivity??? No idea. I don't even know which conductors take part to the loop. But the loops L seems to be about 170 uH ?
Maybe it is not even a pure loop! I'm thinking about Rogers "utility assisted earth mode". Maybe there are a few more resonance peaks for different antenna configurations, like a lazy vertical with gamma match or different loops switched in parallel? Complex!
73, Stefan"
July 19th 2015
Marcus and Stefan have been speculating about transmissions at 1.72kHz (tweek resonance mode) and even whistler mode transmissions.
Waking up early this morning, I took a look at Stefan's garden grabber http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabber.html and was greeted by a fascinating display on his VLF panel.
The screenshot http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_1326.jpg shows a number of narrow tweek-mode resonances at multiples of 1.72 kHz. These are obviously spherics from nearby lightnings, bouncing multiple times vertically between the ionosphere and ground (much the same as clapping your hands between two parallel brick walls). The resonances are rather sharp indicating a high Q-number (ie. around 100 bounces until decay). They are visible up to about 20 kHz, showing unusually small damping of vertical incidence reflections at these ferequencies. There is a small variation of resonance frequency over time, reflecting the variable height of the ionospheric ceiling. The fundamental resonance at 1.7 kHz is probably not visible due to the frequency response of the loop and receiver.
A (somewhat late) screenshot from Blitzortung http://df6nm.bplaced.net/VLF/spherics/image_b_de_150718_0324.png shows the last red crosses between Wiesbaden and Stuttgart passing over Heidelberg at around 1:30.
The tweek resonances were received on the loop antenna in the garden but not on the E-field antenna of the (somewhat whitened out) city grabber http://df6nm.bplaced.net/VLF/spherics/dk7fc_wideband_150718_0330.jpg. This corroberates the notion of near vertical incidence and horizontal H-field polarisation. According to the literature, tweek tails are usually circular polarized as only one sense of rotation exhibits a high reflection coefficient. They are predominately excited by horizontal current components in intra-cloud lightnings.
Of course the resonances will also there in quiet nights without spherics, so they could probably be employed to enhance fieldstrength (up to a factor of Q) for medium-range VLF communication experiments using magnetic transmit and receive antennas. When Stefan still had his earth dipole we already discussed a 2 kHz tweek-mode experiment, which for various reasons hasn't taken place yet. Now it looks like one could even employ the fifth mode near 8.5 kHz...
All the best,
Markus (DF6NM)
May 17th 2015
Joe VO1NA is trying to beat the 10km barrier with a radiated VLF signal. He writes:
Hi Stefan,
30 watts from an audio amp is stepped up with a 1:4 ferrite xfmr.
One end of the secondary is grounded, the other goes to 2 pie
coils wound with 3 strands of 0.08mm wire, L~450 mH R(DC)=437
The 100m wire is about 12 m average height and the aerial current
is about 20mA, with a large uncertainty. 5 km is the best DX,
with about 10dB S/N at 3.3km.
I recall Markus or you posted the maths for erp vs natural noise
on 8 kHz. A reminder would be most helpful!
The 10k race was most gratifying even if I couldn't catch my
pretty little physiotherapist!
73 & TNX
Joe VO1NA
May 4th 2015
More news from Marcus about his recent tests...
Hi Iban,
sorry I hadn't sent the first announcement to the group. I had intended to send only a 2 hour test carrier for Uwe DJ8WX, but as things were going so well I ended up doing a 6 hour transmission ;-)
Unfortunately I can transmit only occasionally when the weather is dry and calm. But not when it is sunny and warm, as my neighbours will then want to enjoy their gardens and be annoyed by the high-pitched beep from the coil. My signal is also rather weak because antenna current and ERP are limited by the 25 kV voltage withstand of the antenna and coil.
Anyway I'm glad to read about your interest in amateur VLF operations. It's not an easy undertaking but certainly rewarding!
All the best,
Markus (DF6NM)
Hi,
I'm interested in receive your signals at 8270, but dont know I dont received the mail in the list.
When you will be online again?
Tnx
73! Iban
eb3frn
May 2nd 2015
News of VLF activity from Germany.....
"Hi Uwe, LF,
the carrier has been on 8270.000 Hz continuously from 8:22 to 14:33, with radiated power around 10 microwatts as usual. It's well visible now on the DK7FC and OK2BVG grabbers, and somewhat patchy on Paul's steerable VLF-spectrogram.
All the best,
Markus (DF6NM)"
Paul Nicholson replied...
"Yes, there is something wrong with the phase. The problem is at my end - looks like a software change to the receive
timing about a week ago has produced a problem.
There is, intermittently, a lot of spiky phase noise. It is a delicate compromise between responding quickly to A/D clock drift
and maintaining a low phase noise.
Today I will fix it, if necessary I'll revert to an earlier version.
Your signal is somewhere between 0.05 and 0.10 fT and that should have produced a quite solid trace on the spectrogram."
Apr 5th 2015
News of VLF activity in Canada by VO1NA ...
Sent: Sunday, April 05, 2015 12:33 AM
To: rsgb_lf_group@blacksheep.org
Subject: LF: VLF in Canada
Dear Group,
Last summer, my VLF CW signals were copied outside my back yard. Today,
using a Marconi XH-100 with a SRA-8 mixer & AD9850/Arduino LO and a
National LF-10 preselector, the sigs could be clearly heard outside my town
with a 20 metre wire aerial strung between the car and a road sign. For
TX, the 100m wire (~15 m high) was coupled with 425 mH to a variac (2:1) in
series with a 5:1 ferrite xfmr to the keyboard amp with the volume control
set to 5 (about 30 watts).
This is DX record on 8.277 kHz for this station -- 1.25 km! I wonder how
far away it could be copied with QRSS? Any TA attempt will have to wait
until a higher Q tuning coil appears. The DC resistance of the current one
is almost 1k and I think it has much series capacitance. It gets warm
and emits an stench of ozone when in use.
73
Joe VO1NA