All this stuff came out at the inquest into the people shot in Gib. The
claim was made that the security forces should be able to jam the signal.

They explained in some detail why they couldn't.

They certainaly could jam the signal, what they could not do eaisly is
detonate the device when they wished.

It seems that the IRA people used a Trio Radio Amateur 144 MHz pocket
radio
system that requires a sequence of reversals transmitted by VHF FSK to
trigger an open channel. The sequence is set by a row of five
thumbwheels,
each of ten digits.


As a matter of interest the bomb intended for Gibraltar was NOT radio
controlled, it was a timer device that was found in the car (still in
Spain).

The SAS did not know this, however, and were acting on what had become
common practise for the IRA in N Ireland from the mid 70's, which was to use
radio control.

Jeff