Purpose / Problem
The aim is to track (large) insects, similar-ish to the approach in this paper. In my design I have a series of high-gain transmitters that rotate. The insect carries a device that records when these signals reach it*. Later the device is recovered and read, and the path is reconstructed.
The problem is what to use to generate the (GHz)** signal.
I tested a prototype 5-6 years ago:
- The device on the bee consists of: a tiny battery (e.g. this one), a simple receiver/detector and a microprocessor (e.g. an atTiny).
- A handful of ~GHz transmitters are placed around the landscape, each with a high-gain antenna (satellite dish) on a rotating platform (rotating at about 50°/s). Each one is sending, encoded as simple on-off keying***, about 8 times per second:
- the angle it is facing (7 bits)
- the time to the nearest 3 seconds, modulo 96 seconds (5 bits)
- the transmitter ID (3 bits)
- needs about 120 bits/s
- The bee-device regularly wakes to see if there's a signal. If there is, it stores the time, angle, and ID.
Work done so far
For the experiment I just put a WiFi dongle in the focus of a (parabolic) satellite dish (but I didn't try modulating it on/off). The approach seemed to work, in that I could detect from 10s of metres when the dish was pointed at the detector.
The dongle was great in that it needed no RF expertise. I'm looking for a solution that requires as little RF electronic construction as possible. One ludicrous approach could be to use the ESP12 (datasheet, power output = 20.5 dBm) and hope I can somehow toggle on/off the WiFi signal, but this doesn't sound very promising. I just wonder what else there might be?
I wonder if I need to just hook up a GHz oscillator (e.g. this) to an RF amplifier (e.g. this) and feed that into a dipole (placed at the dish's focus). I suspect that this is not at all simple, so I'm wondering what simple module exists that makes ~2.4 Ghz (at 20 or 30 dBm+) and has an 'enable' pin that I can toggle on and off, with as little electronic work as possible (ideally I don't want to have to design PCBs etc.).
A note about interference etc.
(To answer these points before they're raised.) At the moment I'm just looking at what is practical, with the aim of having a device and system that could be built without too much RF expertise by ecologists, etc. Obviously, even just putting a WiFi-dongle in the focus of a satellite dish is technically against the rules. I'll be finding out how to do this work without causing interference etc. to others. More info is on the ofcom page.
* I'm mainly interested in bumblebees which forage within a few hundred metres of the nest, to give an idea of the range needed.
** If it's in the GHz range, it means the antenna on the device on the bee is small enough to carry.
*** This makes the bee-device RF electronics simple (an inductor, a capacitor, a large loop antenna, and a diode).
Edit: What are you using to generate the OOK signal? This will be some simple microcontroller (maybe another arduino/ATtiny). That also controls the stepper motor that rotates the antenna, etc.