RHCP

2 Articles

Using An Old Satellite To See The Earth In A New Light

July 8, 2023 by 6 Comments

Snooping in on satellites is getting to be quite popular, enough so that the number of people advancing the state of the art — not to mention the wealth of satellites transmitting signals in the clear — has almost made the hobby too easy. An SDR, a homebrew antenna, and some off-the-shelf software, and you too can see weather satellite images on your screen in real time.

But where’s the challenge? That seems to be the question [dereksgc] asked and answered by tapping into S-band telemetry from an obsolete satellite. Most satellite hunters focus on downlinks in the L-band or even the VHF portion of the spectrum, which are within easy reach of most RTL-SDR dongles. However, the Coriolis satellite, which was launched in 2003, has a downlink firmly in the S-band, which at 2.2-GHz puts it just outside the high end of an RTL-SDR. To work around this, [dereksgc] bought a knock-off HackRF SDR and couple it with a wideband low-noise amplifier (LNA) of his own design. The dish antenna is also homebrewed from a used 1.8-m dish and a custom helical antenna for the right-hand circular polarized downlink signal.

As the video below shows, receiving downlink signals from Coriolis with the rig wasn’t all that difficult. Even with manually steering the dish, [dereksgc] was able to record a couple of decent passes with SDR#. Making sense of the data from WINDSAT, a passive microwave polarimetric radiometer that’s the main instrument that’s still working on the satellite, was another matter. Decoded with SatDump and massaged with Gimp, the microwave images of Europe are at least recognizable, mostly due to Italy’s distinctive shape.

Despite the distortion, seeing the planet’s surface via the microwaves emitted by water vapor is still pretty cool. If more traditional weather satellite images are what you’re looking for, those are pretty cool too.

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A Quick And Easy Tape Measure Turnstile Antenna For MILSAT Snooping

June 30, 2023 by 16 Comments

The number of satellites whizzing by over our heads at any moment is staggering, and growing at a rapid rate as new constellations are launched. But sometimes it’s the old birds that are the most interesting, as is the case with some obsolete but still functional military communications satellites, which thanks to a lack of forethought are largely unsecured and easily exploitable. And all that’s needed to snoop in on them is a cheap ham radio and something like this simple and portable satcom antenna.

As proof of the global nature of the radio hobby, the design in the video below by Brit [Tech Minds] borrows heavily from previous work by Italian ham [Ivo Brugnera (I6IBE)], which itself was adapted to use 3D-printed parts in a German blog post a few years ago. The common thread is the use of tape measures for the elements of the aptly named turnstile antenna, a tried and true material for lightweight, foldable antennas that amateur radio enthusiasts have been using for years. The antenna is similar in design to the classic three-element Yagi-Uda, with a crossed pair of driven elements in the middle of a boom that also supports a reflector and a director. Strips of tape measure material are held to the 20-mm aluminum tubing boom with 3D-printed brackets. A phasing harness of precisely cut coax cable connects to the driven elements and runs down the boom; the quarter-wavelength loop serves to introduce the 90° phase shift needed for the circularly polarized signal from the satellites.

A quick scan with a vector antenna analyzer showed just how well this antenna performs on the 220-MHz band, and the antenna was easily able to pick up the Brazilian satellite pirate’s chatter. The tape measure elements make the antenna easy to handle and foldable, not to mention pretty cheap to build. And what’s not to love about that?

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