Hello Stefan,
yes, you understood right: I am preparing for a test with a big earth base of
some 100m. I will announce it here.
For my first tests with an audible signal in about 100m distance I used no TV
transformer but an audio transformer.
Now with the TV transformer the signal is much louder.
Once again: Mode: CW, TX 300W > TV transformer > 10h/20t T-antenna; RX AATIS
VLF-RX with whip antenna.
The mean problem and also the reason why I am at the really beginning of my
experiments is that now everything has to be tested under better conditions
than inbetween houses and trees - and also with QRSS and Laptop. I hope I can
tell yomething more this week.
vy73 Horst DO1KHS/DI2AN
-----Ursprüngliche Nachricht-----
Von: "Stefan Schäfer" <[email protected]>
Gesendet: 24.05.2010 23:27:34
An: [email protected]
Betreff: AW: LF: AW: 8.97kHz - Near field and radiated signals?
>Hi Horst,
>
>I remember the times in Februar (or was it Januar?) where you gave us that
>little information about your test on VLF that caused all the following things
>;-) Nice to read the mails that came after taht time and what happend in the
>following weeks :-)))
>So, you also have used a TV transformer on your vertical antenna? Pse, what
>was the voltage you achieved? And what was the distance? What was your RX
>mode? (QRSS...?).
>
>Have i understood that right, you want to try a 800m (or 2x 800m?) ground
>electrode antenna? That would be very nice! :-)
>
>73 es gl
>
>Stefan
>
>________________________________
>
>Von: [email protected] im Auftrag von Horst Stöcker
>Gesendet: Mo 24.05.2010 19:18
>An: [email protected]
>Betreff: Re: LF: AW: 8.97kHz - Near field and radiated signals?
>
>
>Hello Roger, Dreamers,
>if we define near field as < 2 lambda we are talking about everything below 60
>km.With this distance I woul be extremely lucky.
>I also do "walkaround tests" near my garden. But I bet only in the flat field
>one can see what is possible with small antenna an without a big loading coil.
>Out from my garden I tried my 10h/20t Marconi as well as a 30m earth base. The
>Marconi worked better, but not good enough. A TV transformer (must be flyback
>of course) made it much better.
>But all the trees and houses are coupling the radiated signal to earth and
>also the AATIS-RX is very much influenced by them.
>I also assume that the horinontal parts of a wire do the same. So only a
>vertical should work.
>For operation in city environment smaller antennas at the roof top (old CB
>antennas) will possibly work better than the bigger vertical in my garden
>between trees and houses at ground level. It might be worth a test.
>One of the next tests will be with my gig earth base. I have collected about
>800m of surplus wire. Possibly this is another way to even radiate more then
>near field. But I would be very surprised it this was good for any DX.
>I bet Stefans kite antenna will at least be the only way to DX operation.
>Unfortunately this is just portable and just temporary.
>vy73 Horst DO1KHS/DI2AN
>
>
>
>________________________________
>
> Von: Roger Lapthorn <[email protected]>
> Gesendet: 24.05.2010 18:36:28
> An: [email protected]
> Betreff: Re: LF: AW: 8.97kHz - Near field and radiated signals?
>
> Thank you for your fast reply Stefan.
>
> In answer to your questions:
>
>
> * Currently, my TX electrode spacing is 10m, which is the best I can
> manage in my small garden. Both electrodes are as far away from the mains and
> other utility services as I can manage.
> * I have not tried /P transmit testing yet.
> * My nearest ham who will listen/look is 3kms away, but using beaconing I
> am able to go out myself and see how far I can reach. This is what I have
> done so far, going out into the fields behind my house with electrode pairs
> or a loop receiver. Best (by ear reception) DX is 0.35kms, but the system has
> much scope for optimisation still.
> * The largest single turn loop I could erect in my garden would be about
> 50-70 sq m (about 15m top and 4m-5m high). The longest antenna length would
> also be 15m horizontal with some vertical section(s) too.
> * The best DX targets are quite modest: I would like to exceed 1km
> initially with the TX power I currently have (around 4W). If I could reach
> G6ALB in the next village 3kms away I would be delighted. If I got any
> further I would be both amazed and VERY happy!
>
> 73s
> Roger G3XBM
>
>
>
> 2010/5/24 Stefan Schäfer
>
>
> Hello Roger,
>
> For your ground electrodes, ground electrodes may be the best "antenna"
> in some 10...10m. I'm not sure how to calculate field strengths but i just
> know about the 1/d^3 dependency, so twice the distance means 8 times the
> power for the same signal reception, in the near field. But it is the
> question what are the electrodes since there is ever a coupling to the mains
> earth and all the metallic stuff in regions where people are living so this
> dependency might not be valid in your tests. As mentioned here, you could
> benefit from these conductors...
>
> But if you want to reach more distance with an antenna of the same size
> (e.g. of your garden)and the same power, you could try such a TV transformer.
> Take a wire, as long as possible and as high as possible, and apply some kV
> on it by this transformer. It can even be resonated by adjusting the air gap
> between the both ferrite parts. That results in a maximum output voltage and
> thus "ERP". At least this would be a good alternative to your ground
> electrode tests. You could easily compare the reachable distances. Here i
> would use a E field antenna for reception in the near field.
>
> How far is your next receiving amateur radio station away? And have you
> tried to do such tests outside the village/city, just like Jim does it with
> his loop antenna? This could allow you to increase the distance of your
> reception. Here, space is not limited and you could try 2x10m, 2x50m, 2x100m
> and so on and tell us the difference in the feed point impedance at various
> frequencies and your ODX :-) Maybe i will also do some ground electrode tests
> in summer but i am still not sure. The complete receiver of Jim is a really
> good idea to check the QRM situation at a given QTH. Probably i will also
> buit his loop design for such tests... Would be interesing what is the
> maximum distance for a CW reception of my transmitted signal (with the kite
> antenna and 6mW ERP) ;-)
>
> I will also do some near field tests in this week, to compare the
> performance of my 2 grabbers. This will be done here:
> http://www.google.de/maps?f=q&source=s_q&hl=de&geocode=&q=heiligenberg+heidelberg&sll=47.820666,9.312449&sspn=0.106733,0.219383&g=heiligenberg&ie=UTF8&hq=&hnear=Heiligenberg&ll=49.419391,8.704101&spn=0.001616,0.003428&t=h&z=18
> in about 1,8km distance to my grabbers. Power will also be below 100W and
> the antenna wire will be mounted on a tower in abt 15m height. I will
> transmit with this TV transformer on a 40m wire.
>
> Roger, what size is your garden? What is the maximum wire length that
> you can apply and in which height? What is your goal (best DX, a reals QSO
> with the next equipped station or just do some funny tests?)
>
> So, wish you fun and success with your experiments!
>
> 73, Stefan/DK7FC
>
> PS: What is your locator / QTH?
>
>
>
>
>
>
> --
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk <http://www.g3xbm.co.uk/>
> http://www.youtube.com/user/g3xbm
> G3XBM GQRP 1678 ISWL G11088
>
>
>
>
>
>
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