A few months ago, I watched a great 32C3 talk about reverse-engineering the Iridium satellite communication network (video). I wanted to join in the fun, but Iridium signals are weak and require a specialized antenna mounted on a ground plane. My plan was to design a custom circuit board with a patch antenna, amplifier, and filter. I ordered some parts, and they sat on my desk because I didn't have time to design the PCB.

Today, I got impatient and thought to myself, "what is the simplest thing that might actually work?" I dug around in my many drawers of junk and found a piece of copper clad fiberglass, drilled a 1/8" (3.2mm) hole in it, attached the patch antenna, and soldered an SMA connector on the back side.

Iridium Antenna Hack (top)
Iridium Antenna Hack (top)

The SMA center pin is soldered directly to the patch antenna pin coming through the hole in the copper clad board. The other SMA pins are soldered to the copper cladding. There's no electrical connection between the cladding on the two sides of the board, which I'm sure is not ideal, but might be good enough…

Iridium Antenna Hack (bottom)
Iridium Antenna Hack (bottom)

I took my PortaPack and fancy new antenna into the back yard, tuned around 1623 MHz with the RF amplifier and gains turned up quite high. What did I see? Packets!

Here's several channels simultaneously visible in Inspectrum. The characteristics match descriptions I've found online (90ms frame interval, 41.7kHz channel spacing).

Wide view of Iridium bursts on several frequencies
Wide view of Iridium bursts on several frequencies

Here are some individual bursts:

Iridium bursts on multiple frequencies
Iridium bursts on multiple frequencies

Now to download the project source from the 32C3 talk, and see what I caught! While this hack worked out well, I think it'd still be valuable to put together an antenna + amplifier + filter combination and be able to pick more packets out of the noise.