Decoding APRS AFSK Telemetry

This page shows you how to configure your PC to decode the AFSK telemetry received from the CubeSatSim.

You can use a Raspberry Pi with OpenWebRX or Direwolf, or you could use a Windows computer with SDR#, VBCable, and AFSK 1200 Decoder software, Direwolf, or Soundmodem. There is also a command line Windows approach Windows automatic AFSK telemetry decoding.

For the latest CubeSatSim, the recommended approach is to use the FoxTelem software, which works with the RTL-SDR or FunCube dongles and automatically demodulates and decodes the DUV FSK or BPSK telemetry. The instructions for this are here.

If you have an older CubeSat Simulator or wish to manually demodulate the signal in your computer or take audio from a radio into your computer, then you can use these instructions.

These instructions assume that you have installed and configured a PC SDR ground station. For example, for AFSK telemetry, SDR# should be tuned like this (this shows the 440 MHz frequency of the older hardware, more recent hardware uses the 434.9 Mhz frequency):

In order to connect (or "pipe") the audio from SDR# to the your decoding software, we need to use VBCable Audio Piping on Windows, or Soundflower on Mac https://rogueamoeba.com/freebies/soundflower.

Once you have the audio as in input, you can now configure your telemetry decoding software.

In FoxTelem, your Source input should be either the Primary Sound Driver or VBCable Cable Out. Make sure the AF box is checked for Audio Frequency. Select Start and if your SDR is tuned correctly, you should decode packets. Note that for DUV FSK telemetry in SDR#, you need to uncheck the Filter Audio button or the low frequency telemetry will be filtered out. Note that some Web SDRs also filter out the low frequencies.

To decode AFSK 1200 APRS telemetry in Windows, you will need to download AFSK 1200 Decoder software:

https://sourceforge.net/projects/qtmm/

Run the software afsk1200dec.exe For input, select "Cable Output (VB-Audio Virtual)".

Click the triangle to start. In SDR#, make sure you are tuned into the AFSK radio signal, and that the audio is unmuted and at full volume. The decoded packet should appear in the window.

In AFSK 1200 Decoder, you should see green and red bars on the level each time a packet is received.

After you have enough packets, click on the packet window, Select All, Copy, then switch to your spreadsheet.

Download the telemetry analysis spreadsheet at https://github.com/alanbjohnston/CubeSatSim/tree/master/spreadsheet Note that there is an online spreadsheet if you have a Google account but don't have a spreadsheet application. https://cubesatsim.org/telem On the online spreadsheet, you will need to make a copy so you can edit it. On the downloaded spreadsheet, you will need to open the spreadsheet and Enable Editing by clicking the button:

In the Data Input tab, position the cursor at the top (A1) and paste the data.

Now look at the Current Graphs tab and you should see updated graphs.

You can also look at the Voltage and Temperature Graphs.

In order to update the graphs, you will need to clear the existing data then copy and paste new data from the AFSK 1200 Window. Note that only 80 data points are graphed (data in A1 - A161). To clear the existing data, go to the Data Input tab in the spreadsheet, then highlight the cells with the data (e.g. A1 through whatever row has data in it). If you are using Excel, right click then choose Clear Contents. If you are using the Google Docs online spreadsheet or Libra Office, hit Backspace. Don't delete the cells or the formulas may become broken. If this happens, even with valid data, the graphs will be blank. If this happens, you will need to download the spreadsheet again from Github and then paste in the data again.