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LF: Re: Band 472_479

To: <[email protected]>
Subject: LF: Re: Band 472_479
From: "James Moritz" <[email protected]>
Date: Sat, 18 Feb 2012 17:24:06 -0000
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Dear Lubos, LF Group,

I have a similar problem operating on 500kHz (and it will also be similar for 475 kHz) at my QTH. In my case the source of wideband QRM appears to be low-level sidebands of broadcast stations (there are 4 broadcast TXs within 1km of my QTH with 400kW total power). The noise has a continuous spectrum, and is about 20dB above the band noise level. Using a vertical antenna, it is only possible to hear local signals, but over the years I have been reasonably succesful using simple loop antennas, or loop and vertical antennas combined with a phasing network, to produce a directional null that practically eliminates the QRM from this source. Of course, the limitation of this technique is that wanted signals are also eliminated if they are in the same direction as the noise source; unfortunately the BC transmitters are east of my QTH, making it difficult to receive stations in mainland Europe, but signals from most of the UK, Scandinavia and North America are not seriously affected, and much reception is still possible. In your situation, using an antenna with a directional null would also have the advantage of reducing the level of the beacon signal itself.

Cheers, Jim Moritz
73 de M0BMU


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