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 <[email protected]>
    

        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/
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    G3XBM    GQRP 1678      ISWL G11088
    

  


    
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