Tiny Transmitter Tracks Targets

It is a staple of spy movies. The hero — or sometimes the bad guy — sticks a device never any bigger than an Alka Seltzer to a vehicle or a person and then tracks it anywhere it goes in the world. Real world physics makes it hard to imagine a device like that for a lot of reasons. Tiny power supplies mean tiny lifetime and low power. Tiny antennas and low power probably add up to short range. However, [Tom’s] Hackaday.io project maybe as close as you can get to a James Bond-style tracker. You can see a video of the device, below.

The little transmitter is smaller than a thumbnail — not counting the antenna and the battery — and draws very little current (180 uA). As you might expect, the range is not great, but [Tom] says with a Yagi and an RTL-SDR he can track the transmitter on 915 MHz for about 400 meters.

As you might expect, the circuit is simple. A low frequency oscillator (about a half hertz) triggers an RF oscillator with a SAW resonator.  A bipolar transistor drives a simple whip antenna. The schematic and some more details are over on Instructables.

Thanks to the half-hertz timing, you get a beep about every two seconds which is probably good for battery life and sufficient for tracking. Just don’t expect a GPS coordinate tracker that you can receive from your secret lair a half a world away and you’ll be fine.

If you have more space and power, you can get a little closer to the spy’s dream tracker, but only a little. If you want to track something with a live USB port, you can always see how much you can jam into a USB drive casing.

16 thoughts on “Tiny Transmitter Tracks Targets

    1. There are a bunch of fairly cheap RF transmitter and transceiver chips with similar capabilities. If you’re willing to tolerate low data rates, the horizon is the limit even for low (few milliwatt) power transmitters. High altitude balloons are a great example of this — in areas where regulations limit the transmitters to 10mW, people still track balloons from hundreds of kilometers away. The UK High Altitude Society is worth looking up if you’re interested in this sort of thing.

  1. ” Real world physics makes it hard to imagine a device like that for a lot of reasons. ”

    I imagine much more capable SDRs mean the entire frequency bands would be your ocean as it were. Adaptive transmitter that fits into a changing environment.

  2. Really neat system. Is interesting the package size and distance range of the remote control modularized systems that are really cost effective and on the COTS market. I was recently looking into an OSD for a ATV system and realized… man… the OSD systems for the drones and even with a ARM controller even seems more cost effective. Higher definition like 4K is a little different. Still, interesting and compact.

  3. Thanks to the watch only a ham could use (and some other project I’ve forgotten), I’ve taken an interest in the CC43F137. MPU (with arduino like ide) and 315-920Mhz transceiver in a 10x10mm package. Every tag can have a unique ID and with an accelerator/gyro you’ll know if they spotted the tail and floored it or ducked down a side street and parked with the lights off.

    Hmm remind me to add a RTL-SDR frequency sweeper setup in my next getaway vehicle.

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