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?
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