Updated 3/21/19
We’ve now installed the EZ-Lindenblad antenna (the QST version with modifications – the AMSAT alternative wasn’t available at build time) and found that it works quite well. Thanks to G0KLA’s recommendation we’ve set the Auto-Start function on, which will use the Doppler correction to follow the currently-visible satellite rather than searching the entire passband for the strongest signal. This has significantly increased our packet capture rate.  We’re now planning to install the 1.07 version of FIAB.

Updated 12/8/18
AMSAT has launched and maintained three “Fox“-type satellites that are easily available for ham use. They’re in low-earth orbit and use standard 2 meter FM transmissions, and can occasionally be worked with an HT. A fourth satellite is scheduled to be launched on December 2 2018.

In addition to audio QSOs these satellites transmit telemetry information about various parameters related to the health of the satellites that are monitored by ground stations. This data is transmitted using a low audio frequency underneath the voice signals during a normal QSO using a “data under voice” (DUV) technology – so you can’t hear it but it can be decoded. One of the telemetry screens for AO-85 looks like this:

Since the satellites orbit over all parts of the earth, it takes a network of stations to continually monitor the telemetry to give AMSAT a continuous stream of data. AMSAT distributes a free Fox telemetry program for Windows, Mac and Linux for users who want to download and view this telemetry. That program can optionally upload the telemetry to the AMSAT data warehouse, allowing AMSAT to record satellite performance as it flies around the earth.

Fox in a Box

To facilitate monitoring and reporting this data, AMSAT has developed a program for the Raspberry Pi computer connected to an SDR radio that provides a self-contained station for receiving and uploading the telemetry data. Called “Fox in a Box” (FIAB) it’s pretty easy to implement and can be left alone to function (although we never really leave anything alone in our ham projects…). As far as I can tell the only source of this software is the AMSAT store where you can buy an SD card preprogrammed with the software. This card already has VNC installed and enabled, which is how we connect to the Pi that’s running it.  The card also comes with instructions on installing the software.

Our Project

We all know that this rarely happens – but it worked the first time! As the satellite rose above the horizon the “Input” telemetry page started showing the “eye” pattern that indicates a decodable signal. The “Frames” counter at the bottom of the screen started counting up from zero and the values in the telemetry screen shown above moved from all zeros to their current values. Because of the excellent antenna location at the clubhouse we were able to collect telemetry from horizon to horizon throughout the pass. We had the same experience about an hour later with the next Fox pass. We modified a few parameters later, but it basically worked out of the box. Because there’s a VPN connection to the clubhouse available I can monitor this from home by connecting to the VPN and running VNC to connect to the Pi.

How the software works

The software is really cool. First, it tracks the satellite itself without any external components. It automatically downloads the Keplerian elements from the AMSAT website and does the orbital calculations internally. Note in the upper right screen that AO-91 has a positive elevation value, which means that it’s above the horizon. Note in the horizontal window at the bottom of the screen that the frequency band for all of the Fox satellites is shown, with the freq for each satellite delineated with purple lines and the strength of each signal within that band shown on the red line. This is a cool feature of using an SDR radio like the FunCube – it can scan the entire bandwidth for telemetry signals and lock onto the one that it finds. (I don’t know if it only scans for satellites that are above the horizon – perhaps a knowledgeable reader of this blog can clarify that point.) So you can see the vertical purple bar over the peak in the red line in the AO-91 section of the band, which is the telemetry signal being received.

Reporting leadership

As of 12/1 we’ve downloaded 1100 telemetry frames that have been uploaded to the AMSAT data warehouse. We’re far from being a leader in telemetry reporting, since the leader has more than 600k frames, but we’re in the top 100 for the most recent 7 days as of 12/1/18. That’s pretty cool too.

Next Steps