After serious thinking Matty F wrote :
On Mar 14, 12:17 pm, Harry Bloomfield
wrote:
Matty F submitted this idea :

I am the only person
alive who knows why it works at such a high frequency,

..and that would be something to do with the MOD or Civil Defence?

No it's just a commercial secret which I discovered! However I should
probably give it away before too much longer. So what use is a high-
quality audio transformer these days?

Multiplex?

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk