Homemade waveguide antenna for FPV racing timing gate

Quadcopter FPV racing has quickly grown into a competitive sport in the past few years. As a result it has become necessary, like in all other racing hobbies, to keep track of lap times. This is usually done using IR transmitters and receivers. However, in the case of FPV vehicles this timing can be done without extra IR or RF beacons. By making use of the already present video transmitter on each vehicle, it is possible to keep track of every vehicle in the race using their specific video channel assigned to them. However, there are some problems associated with using the 5.8 GHz emissions to track the vehicles. The first is the spacial accuracy where a timing event is triggered, the second is the effort needed to continuously monitor the full FPV RF band. This then turns into a antenna and receiver problem.

A very easy and cheap solution exists for the antenna. Using some cardboard, foil and aluminium or copper tape it is possible to build a high-gain wave-guide antenna at 5.8 GHz. A slotted waveguide antenna has a thin disc shape antenna pattern which is perfectly suited for use as a timing gate. Below are some photos showing the construction of the antenna.

Cardboard structure

Cardboard structure

Adding the feed structure

Adding the feed structure

Feed in place

Feed in place

Wrapping the rest of the waveguide in foil

Wrapping the rest of the waveguide in foil

Cutting waveguide slots

Cutting waveguide slots

Testing the antenna

Testing the antenna

The receiver needs to be broadband to be able to monitor all of the vehicles at the same time. For this I would suggest mixing down the antenna signal to below 1 GHz and use multiple RTL-SDR donglesĀ as a low cost solution to detecting all of the multi-copters in real-time.

Unfortunately I have run out of time to work on the receiver. I will upload further data if there is interest in reproducing the antenna or continuing the project.

Posted in Quadcopter, Things.

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