LF: Re: WRC-12 Approves the New 472-479 kHz Amateur Radio Allocation

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

Dear Roelof, LF Group,

> The requirements for the service area of a NDB is a fieldstrength of 70 
> uV/m at the borderline.
> So to cause noticeable interference, the offending signal must be rather 
> strong.
> Many NDB's share the same channel, apparently without problems.
> Unless you actually live in or near the service area of a NDB in the 
> 472-479 kHz frequency range, the NIB regulations won't pose a problem.
The ADF receivers that use these beacons essentially process the carrier 
amplitude and phase received using directional antennas in order to obtain 
the bearing. So the effective bandwidth of the receiving system can be made 
rather narrow; the audio sidebands are mostly there for ID purposes. Since 
there are always many potential QRM and noise sources in the MF range, ADF 
receiver design has evolved to cope with quite poor SNR. So even if you are 
located near or within such a service area, provided you keep clear of the 
actual beacon carrier frequency, ADF receivers will probably not suffer 
harmful interference. This should not be too hard with 7kHz to play with, 
and only a handful of widely scattered beacons within the range - it is only 
common sense to avoid using a frequency where there is a strong beacon 
signal causing you 24/7 QRM!
Cheers, Jim Moritz
73 de M0BMU