S1: What’s so special about 100km from Charing Cross?

The frequency range 431.0MHz to 432.0MHz has a restriction that states that it is not available for use within 100km of Charing Cross, but why?

The Primary User for that frequency range is the UK MoD (Ministry of Defence). Amateur Radio is a Secondary user, and as such can’t interfere with the Primary user. The Primary User in this case has asked that it’s not used within 100km of the centre of London (defined at Charing Cross). There is also an e.r.p. limit in place, which prevents use of a beam antenna at 101kms away from beaming in more than 10 watts.

Why don’t the military want us chatting on 431-432MHz in and around London? Probably best not to ask!

100km of Charing Cross
Map showing a 100km radius from Charing Cross

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