RF object tracking

Hi,
I have an idea for a project and I’m interested if anybody knows if it’s doable.
Is it posible to have a RF beacon and arduino with two RF recivers spaced ,lets say 25 cm(10 in), in the vertical plane so that it measures the time diference of arival of the signal betwene those two? I know that the speed of radiowaves is equal to the speed of light(3x108m/s) and it would be imposible to measure with the arduino clock speed (16x106 Hz =16 MHz) but could I slow down the signal sine wave(let say from MHz to kHz) so that I could measure the time betwen the peeks of the signal? Maybe using some precise clock like chronodot from macetech?
Or am I runing around in circles?

but could I slow down the signal sine wave

How do you achieve a reference?

let say from MHz to kHz

A 1kHz radio signal has a wavelength of 300km.

Have you thought of ultrasound?

Or am I runing around in circles?

Yes. You can't use this technique with this equipment.

Yes I thought of ultrasound. I could send a command through RF to a beacon that then emits a ultrasound ping and measure the time it takes to get back to the arduino. But I think the ultrasound beacon wouldn't work if it's in a persons pocket. Also I'm haveing a dificult time finding ultrasound transmitters and reciver that can be bought separatley as most of them are coupled together as ultrasonic rangefinder. Also I think the range could be the isue. I'd like it to work more than 5m away.

Any ideas where I can buy ultrasonic transmiters and recivers? And what is the maximum range outdoors?

I want to make a pan/tilt rig on which I can mount cameras for filming. It will be similar to the spider cam, but the only difference would be that it would glide on one wire instead of four. Making it radio-controlled is not the problem but I would also like it to be more autonomous so I can press record and not worry about following the person in the scene. I also thought about using a IR emitter and track it with some sort of cam but it would have to be visibly mounted and it would also be seen on the camera I'm filming with.

This is exactly what I want to make. Do you maybe know what is the range of this product(transmitters / receivers)?

Well that would be 10 meters. Is there any way to use this sistem to track up to 30 meters(100 feet)? Maybe to amplify the signal?

Thanks!