LF: Re: Band 472_479

["James Moritz" <james.moritz@btopenworld.com>]

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