Flynn, the short answer is "because it is
their train-set".
I'm sure they do feel uncomfortable at the thought of light aircraft coming and going at night willy-nilly, as would a number of other Govt agencies.
If I had a private strip I'd buy it, install it and use it without giving slightest concern to whatever rules might prohibit it.
Shunter, you do not belong in the aviation community with an attitude like that. You are a disgrace and a danger to the rest of us with that attitude to the rules. Aviation is not an activity for those with a gipsy mentality like yours.
IO540. Yor attitude is little better, as virtually every post you've mad so far recommends or suggests some sort of illegal activity and contempt for rules that were made by wiser people than you for reasons of safety, yet you always appear to know better.
For your (and others') info those frequencies not requiring licences are not exempt from the law, and one of them relates to height of the antenna above ground for reasons of reducing nuisance by excessive range.
and it is a piece of cake to find a frequency not used by any known airport;
It is actually rather difficult to find a frequency in Europe that is not nibbling into the coverage area of another station using the same one at or outside published coverajust ge area, and that is the licenced ones. You are not in posession of a geographical spectrum analysis so you are talking out of your fundament. It is pretty staggering to find someone so ill-informed and actualy peddling such utter crap on this forum. Does it not occur to you that although you have not heard any transmissions from ground level it does not mean that your Tx cannot reach and block someone airborne a hundred miles away, or that you just have't been listening at the right time.
Your attitude stinks too.
What's wrong with just accepting that you aren't allowed to?
Or fitting a decent landing light and using reflectors?
Or just not night flying from your private strip when there isn't enough moonlight to see.
For God's sake. We really get them on this forum, don't we?