Tracking a radio signal

[Mike]

Hey all,

Some of you may remember me from a few years back, I was active on 237 (and these boards) from '04 to '08. Few years later I have a little bit of a project brewing and I needed some people to vet an idea to. What better than to give some off-season guys some thinking to do?

Scenario:
Multiple beacons transmitting on 433Mhz a simple data packet:

SYNC byte
ADDR byte (unique identifier for each beacon)
TX_ID byte (random identifier for each transmission)
CHKSUM byte (to verify integrity)

So lets say we have multiple beacons transmitting in a wide area. What I need to be able to do, flying from approximately 150 feet at relatively low velocity is find a beacon. So I need to take the digital data in, find a unique beacon to choose (for now, randomly pick one) and then get as close as possible to that particular beacon; "home in on it".

Here was the original idea presented to me. Four receivers on all corners of the plane (nose, tail, each wingtip). Small plane, about three meter wingspan. However this may be expanded to a larger (8 meter+) application. Using the transmission ID byte, track the time it takes between hitting each receiver and calculate the distance away, or at a minimum the direction to go. The problem here is that I calculated the speed of a 433Mhz wave at 299,792,000 m/s. That gives us 10 nanosecond difference between hitting two receivers 3m away. I think that idea is pretty much nixed.

Next idea: a receiver antenna on the plane is to be shielded by a rotating tube with a small slit in it. By using the position of the slit when we receive a transmission from the beacon we're looking for we can find out where the beacon is transmitting from.

I've never really dealt with radio waves this directly before, so what I'm looking for is some opinions on the feasibility of my second idea, as well as what kind of antennas and shielding material would work best and avoid detuning, etc.

The project is a pretty cool one with great potential. It involves Unmanned Aerial Vehicles with a unique, necessary and possibly profitable application. If you're in the Space Coast, FL area and would like more information shoot me a PM or email: msorrenti2008@fit.edu

Thanks,
Mike Sorrenti