Receiving Telemetry

Anyone with a UHF-band amateur radio can hear EQUiSat transmissions, but currently the only known way to decode transmissions is using the XDL Micro transceiver board. However, we’re actively working on building a software decoding method for transmissions, so it may be possible to decode transmissions received today in the future!

We’d love to hear from amateur radio enthusiasts who have heard EQUiSat even if the data is not decoded. Raw I/Q dumps from SDR software such as GQRX, Matlab, or SDR# are particularly helpful. You can submit these, demodulated audio samples (FM/AM/SSB), or anything else here. You can also just tweet us that you heard it. We’d very much appreciate your help in keeping up with EQUiSat!

Anything you can send us is helpful, even a screenshot of your SDR waterfall or just a message letting us know you heard it.

The appearance of EQUiSat transmissions in GQRX

The sound of EQUiSat’s telemetry burst (FM-demodulated). This is transmitted every 20 seconds.

The Details

Beacon Frequency: 435.55 MHz

Bandwidth: 12.5 kHz

Transmit Power: 0.5 W

Modulation: 4FSK @ 9600 baud

Callsign: WL9XZE

 

Transmission Frequency

Every 20 seconds, a batch of four 213ms long transmissions 750ms apart. The satellite transmits constantly, but in low power mode the batches are reduced to two transmissions every 40 seconds.

Antenna Information

Half-wave dipole, with an estimated gain of 1.82 dBi

Packet Structure

255 byte packets separated into sections of preamble, “current data”, “historic data”, errors, and parity bytes for error correction.

See here for details on the format and here for a description of satellite signals.

Antenna Orientation

The satellite aligns itself with the earth’s magnetic field lines, which run in an arc from the South pole to the North pole. So, the antenna may be in any orientation around an axis in the same direction of the earth’s magnetic field lines. Note that these field lines (and thus EQUiSat’s flash panel) point more towards the earth as the satellite moves north.

Why can’t EQUiSat’s transmissions be decoded as conventional 4FSK?

Although the XDL Micro we use reports 4FSK modulation, it is a non-standard format, with FSK deviations of 2.4 kHz and 2.8 kHz from the center frequency.

We have configured the radio to use “transparent mode” such that the data is encoded transparently (without scrambling or encryption) onto the 4FSK protocol, but because the modulation format is non-standard, most 4FSK decoders cannot decode its transmissions.

We are currently investigating other options, including GNU Radio, to decode the XDL’s transmissions. We always appreciate help or suggestions, so please reach out!