The Alexandra Palace Television Society has made available on YouTube the TV programme, The Secret War – Battle of the Beams, originally transmitted on January 5, 1977.
This tells the story of how the UK jammed high frequency radio beams used to direct German bombers to their targets during night raids in World War Two.
Part Two:
Part Three:
Part Four:
Part Five:
The Alexandra Palace transmitter was used to jam the Y-Gerat system which operated in the 40-50 MHz range. The earlier Knickebein system operated in the 30-31 MHz range.
A BBC London report on the use of Alexandra Palace during World War Two is at:
http://news.bbc.co.uk/local/london/hi/people_and_places/
history/newsid_8231000/8231874.stm
Thanks to southgate ARC for the original article which can be found HERE.

(click to enlarge)