Re: LF: AW: 8.97kHz - Near field and radiated signals?

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Stefan (et al),

I have created a map showing my location on Google Maps. See http://maps.google.co.uk/maps?hl=en&tab=wl&q=cb25%200hf. Click on the blue pointer. You will see the fields nearby in which I have been receiving the test signals.

73s
Roger G3XBM

2010/5/24 Stefan Schäfer <schaefer@hst.tu-darmstadt.de>

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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