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.
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Current VLF receptions of transmissions by DK7FC_resized.jpg
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