I want to switch a light (or a circuit controlling a light) on and off from a distance of nearly 20km. There is line of sight between the two locations, across a valley. The set up is to be used for a one-off experiment in the UK, and is expected to last about an hour. I don't have a ham licence (but did do the non-morse course years ago), so suggestions for licence-exempt frequencies are welcome.
Both items need to be carried - by human - to locations in countryside and operate on batteries, so I need a sensible size (no car batteries!) for each. The receiver's location is several miles from the nearest road. It would be good if the transmitter was a small pocketable hand-held device - I want to be able to operate a camera between switching the light on and off.
My thoughts thus far are some sort of CW transmitter, with the actual keying being done using a PIC (I have some experience coding PICs, and making a working cct shouldn't be an issue). The receiver would listen for the series of pulses (say, morse for ON and OFF), and respond accordingly.
Doing metalwork for making antennae is no problem - provided I have some idea of the shape(s) I need. On the assumption that the licence exempt frequencies are low power, would I be right in thinking that a directional transmitter antenna would be a good idea?