The book "Winning the Radar War" says - " in the January 1935 test, Watson-Watt used the BBC 13-metre Empire transmitter at Daventry. The experiment was to demonstrate that radio transmissions would bounce off a Heyford aircraft,flown from Farnborough................." " The equipment was installed in a GPO Morris truck by Wilkins. Wilkins and the GPO driver spent the night in the truck near Weedon, ready for an early start the next day........ The aircraft was detected at a range of seven miles."