Summary from DK7FC 20101023 VLF TX tests at SQ5BPF QTH
wersja polska english version
The signal was received by SQ5BPF in Warsaw, Poland loc. KO02MD. Stefan DK7FC was transmitting on VLF 8970Hz, 6470Hz and 5170Hz, with a 200m (and 300m for 5170Hz) antenna supported by a kite. With abt. 550W input, the estimated ERP was 27mW for 8970Hz, 11mW for 6470Hz and 2mW for 5170Hz. Distance from SQ5BPF is 904km. The mode was QRSS600 DFCW.

The receiving setup was using a PA0RDT miniwhip-like antenna, with a bandpass filter (simple one stage LC filter, and 1 stage 20dB amplifier). The output was sampled using the internal sound card of a DELL Lattitude E4300, received under Spectrum Lab v2.75b12 under wine under linux. Sound card frequency drift was compensated by locking it to the military station DHO38 transmitting on 23.4kHz.
DK7FC's CoilDK7FC kite with the antenna


In order to monitor the transmission a temporary grabber established. All times are in local time, substract 2 hours to get UTC.

33km band - 8970Hz

The whole transmission (long carrier and "GM" transmitted in DFCW):


The S/N ratio was abt. 20dB (one grid is 20dB, FFT resolution is 3.8mHz):


You can see the whole screen from the grabber HERE

Stefan's signal was also perfectly readable with a wider 30.5mHz FFT resolution, with abt. 5dB S/N. This is comparable to QRSS60:

You can see the whole screen from the grabber at QRSS60 HERE

46km band - 6470Hz

The whole transmission (long carrier and "K" transmitted in DFCW):


The S/N ratio was above 20dB (one grid is 20dB, FFT resolution is 3.8mHz):


You can see the whole screen from the grabber HERE


58km band - 5170Hz

The whole transmission (long carrier and "K" transmitted in DFCW):


The S/N ratio was abt. 10dB (one grid is 20dB, FFT resolution is 3.8mHz):


You can see the whole screen from the grabber HERE

Stefan's letter to the rsgb_lf_group mailing list:

Dear VLF,

So, now after another very successful VLF experiment i want to
summarise some informations and achieved results.

First i want to thank all those who did and tried to receive my VLF
signals on up to 3 different VLF bands! Without so many RX stations,
increasing and increasing numbers, it would not be worth to do that
effort all the time, especially the 300m kite!
Thanks for so many RX reports! There are very interesting and
different results from different stations. Here, we can learn a lot
of VLF propagation and suitable RX systems, it seems.

Special thanks to Marco/DD7PC who was available on the phone to
inform me and made QSP to the reflektor!

Most amazing seems to be the results of the 5170 Hz receptions of
SQ5BPF and OE3GHB, with a very impressive S/N! Please, can we have a
detailed RX antenna description and some wideband (0...24 kHz)
screenshots? As far as i know both of these staions are using E field
antennas!!

Congratulations to the successful receptions! As far as i know, in
my 8th experiment there have been the following results(new= bold;
new ODX=underlined; (distance/km)):

Dreamers Band / 33km / 8970Hz:
Daniele Tincany(707), DK7FC(40), M0BMU(657), DD7PC(53), DJ2LF(176),
DJ8WX(461), DK6NI(165), DL3ZID(462), DL4YHF(264), Michael Oexner(72),
EI8JK (1310!!!!!!!!!!!!!!!!!!!!!! :-) ), F1AFJ(683), IK1QFK(544),
OE3GHB(594), PA3CPM(367), PA3FNY(360), SQ5BPF(904)

46km / 6470Hz:
DD7PC(53), DK7FC(40), IK1QFK(544), M0BMU(657), Micheal Oexner (72),
OE3GHB(594), PA3CPM(367), PA3FNY(360), SQ5BPF(904!!!)

58km / 5170Hz:
DD7PC(53), DK7FC(40), OE3GHB(594), PA3FNY(360), SQ5BPF(904!!!)

There have been some stations without a successful reception. I think
in most cases this is due to a non optimal RX antenna or to much QRM.
But both cases can be optimised. QRM=> going out in the field (like i
do ;-) ), insufficient effeciency=> optimising the RX antenna. In the
case of W1VD, i assume neither the RX nor the QRM is the problem.
Here, i/we have to find the best time for such a test to USA. And: It
is nice that the ODX is increasing in "small" steps. That makes it
very exciting, isn't it? :-)

The new DX record by amateurs on VLF is acquired by Tony/EI8JK, 1310
km. It is very interesting that he used a E/W orientated "earth
antenna" to receive the signal! He already told me that he found some
methods to strongly improve the S/N! Although the color scale of the
capture is a little dark, it is an undoubtly reception. If it could
be with even better S/N, as he means, there should be some chance to
reach even more distance! We will see..

So, here my report and some data of the 8th experiment:
I arrived on the hill at 5 UTC. It was almost dark and the temp was
below 0 C. The moon enlighted the field, and the sun started to
enlight the sky. There was no wind at all! As i finished building up
the system, the sun came out, at 6 UTC. Still no wind but it came up
slowly. At arround 8 UTC the kite was up and the wind increased to an
optimal level without breaks. So i could transmit a long carrier (1
hour), GPS locked, at 8969.975 Hz. After that i had the idea to
transmit a short mesage in DFCW-600: "GM- good morning" ;-) This was
successfully received by 17 RX stations in 8 countries!
The kite was stable in an angle of about 70 deg an the average
antenna current was about 900 mA, peaking 1 A, so 16 kV rms on the
wire. Since the earth lossed seemed to be higher, a TX power of 550 W
was necessary this time. This seems to be the limit of this generator
but the coil/wire/PA will at least handle 2 kW, i assume! There was
no noticable temp rise at the PAs heat sink during this 1 hour
transmision! :-) So, the ERP was once again up to 27 mW.

Marco/DD7PC kept me informed about the traffic in the reflector, tnx.

After that it was possible to make QSY to 6470 Hz just by changing
the transmit frequency (within SpecLab!) and the tap of the coil. It
took maybe 2 minutes to become QRV there on 46 km, as can be seen on
the captures. On 6470 Hz, the coils losses are 100 Ohm higher. The
achieved antenna current was 900 mA. Since the wind was even stronger
to that time, the average current was 900 mA as well, 20 kV rms on
the wire. Thus the maximum ERP here was 11 mW.

Since the generator was running at full power it took very much fuel
in a short time and i thought this could become a problem since i
wanted to try a 300m vertical antenna at 5170 Hz as well. So i
decided just to transmit a 40 min carrier for long time integrations
and a "K", to have a trace that can be undoubtly identified as my
transmission. During that time i rolled out the 100m kite antenna to
switch it in series to the 200m antenna later (exciting experiment!).
The wind increased even more during that time and so it took some
time to become QRV there on the 58 km band.

I decided to exchange the kite to the smaller version (3.6m^2). This
"small" kite took the whole kite line and the 300m wire until i
pulled it down after the 5170 Hz test. But the angle of the antenna
was lower, maybe 60 deg (sometimes 70 deg). First a applied my DDS
VFO since the resonance can be easier found with the durning knob
instead of a SpecLab slider. But this frequency seems to cause EMC
problems in the VFO although it is driven by a battery and the output
is fed into the PA by a fiber optic cable! Not so the PC! SpecLab
generates the TX frequency and supports the audio output. I used a
homemade fiber optic link (using the 5V of the USB as the power
supply) working with a class A LED driver.
I found that 5170 Hz is not the resonance frequency of this antenna.
Actually it is higher, at arround 5290 Hz! At 5290 Hz i got about 850
mA average antenna current! But i decided to stay at 5170 Hz since i
wasn't sure about the QRM situation on other frequencies and most of
the RX stations (including my grabber) are focused on this QRG, i
assumed. With the variometer adjusting for minimum L i reached an
average antenna current of 400 mA on 5170 Hz, so about 6 dB more ERP
could have been possible with a suitable QRG or wire or coil! This
means, the voltage on the wire was about 7 kV rms and the ERP just 2
mW (!)
Anyway, Gerhard/OE3GHB received the 5170 Hz signal with about 20 dB
S/N in 594 km distance, just about 10 Lambda ;-) !! (and SQ5BPF at 10
dB).


We should think/ask about how this can be possible!! I do not think
that it is just due to low QRM and a good antenna but due to the
propagation as well!!???
I will repeat the 5170 Hz tests and will try to make the wire a
little longer :-) 5170 Hz is critical for some RX locations since the
local mains hum is already an issue there. But this is just a new
challenge to take, isn't it? ;-)

Now, since i know that the resonance of the 300m wire is at 5290 Hz,
i know where to make a 3rd (and last) tap on the coil to come back to
8970 Hz with a 300m vertical. This will increase the ERP by another
3...4 dB (reduced coill losses and a factor 2.25 in radiation
resistance).

300m and 5170 Hz is my limit! I will not go lower, sorry ;-) Maybe
the losses and be reduced and/or the power can be increased but here
i will stop, at least with the kite antenna (not with the earth
antenna) :-)

So, looking forward to the 9th experiment that will probably be in
november 2010. Will you be receiving? :-)

Best 73, Stefan/DK7FC

PS: I attach the updated VLF reception list of my experiments. Please
let me know if you are missed or so.



Results from other VLF tests HERE
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