Hello group, dear Stefan!
You are right, I am using a PA0RDT-like antenna. The differences are:
Instead of the original 2nd transistor, I used a 2SC..something. A RF,
low noise, low power (200mW) type because the 2N51xx wasn't available. I
increased the resistor at the emitter from 220 to 390, just to keep the
current lower.
Coils are bigger. Instead of 470µH in the antenna, I used 1mH and in the
power supply even more (~20mH).
Coupling capacitors are bigger. I used 1µF in every case.
I'm sure this isn't making a difference, the original design is working
the same. I just had this parts available and used them.
My "environment" is as follows:
I live in a small town (a bit more than 2500 people) and my plot of land
is abt. 1000 square meters. This is the most common size of property in
this area of our town (wohne in einer sog. "Siedlung"). So the houses of
my neighbours are in average 30m away. There is a motorway or
"Inter-state" (Autobahn) abt. 700m away from my house. So I guess from
the noise, it's and average place. Could be better and could be worse.
The PA0RDT is mounted abt. 5m above the highest point of the roof of my
house on a fibre pole. So in average, this is about 15 to 18m above
ground, because ground level behind the house is abt. 3m higher than in
front. (=Südhang)
As earthing, I use the lightning protection system of the house which
consists of abt. 100m of steel wires (8mm dia) buried in the concrete
foundation, which is about 1,5m deep. Additionally there are some
earthing rods connected.
The rest is plain and simple: A laptop running SpecLab using a slightly
modified configuration as given by Markus, DF6NM on his webpage.
Today, I rearranged my shack and also the grabbers and so for a
requested "wide band"-view from 0-24kHz you can look at:
http://members.aon.at/grabber/VLF (30min Update)
or you can reach this site via a link on my LF grabber:
http://members.aon.at/grabber
I will keep this wide-band view online for the next couple of days.
Looking forward to your next experiment!
73
OE3GHB
Gerhard
Am Montag, den 25.10.2010, 15:40 +0200 schrieb Stefan Schäfer:
> 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, thevoltage 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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