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Aerial grounding and QRM pick-up: theory & practice
Hi group,
I'm a SWL and am specially interested in Navtex DX-reception.My problem is (was) the heavy QRM from about every TV-set, monitor, PC in the neighbourhood. I'm currently using a T-aerial: horizontal wire 20 meters long, ca. 10 meter above ground, vertical part ca. 10 meter down from the middle, = 1:9 "magnetic" balun = 25 meter RG58 to receiver. Receiver is located on the first floor, and is grounded via a thick wire to the earth pin of the house. Typical reception sounds like this: http://users.pandora.be/dirk.claessens2/div/not_grounded.wav ....humming, hissing, hard to decode, nightmare. In despair - and against all advise in antenna textbooks (ground loops!) - I decided to make an additional earth point at the balun. I drove two 1 meter 1/2 inch copperpipes into the ground, and connected these to the shield of the RG58 at the balun. Grounding at the receiver was unchanged. The result was stunning: http://users.pandora.be/dirk.claessens2/div/grounded.wav QRM totally gone! Can anyone explain this? Thanks for any insight - Dirk |
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