Telemetry Panel

The Telemetry panel shows the telemetry frames that SkyRoof decodes from the satellite signal. SkyRoof can decode the telemetry transmitted by many satellites without any external software: the built-in decoder demodulates and deframes the signal directly from the SDR, right inside the program. Unlike the external decoder and sound modem workflows, it needs no separate program, no Virtual Audio Cable, and no output stream — SkyRoof feeds the Doppler-corrected receiver passband straight to the decoder.

The panel is opened from the View / Telemetry menu. Its optional outputs — saving to a file, sharing over a KISS server, and uploading to SatNOGS — are configured as described in Setting Up Telemetry Decoding.

Supported Signals

The decoder supports the FSK, GFSK, MSK, GMSK, AFSK, BPSK and DBPSK modulations with the framing formats used by the supported satellites. The modulation, baud rate, and framing are looked up automatically from the transmitter description in the satellite database, so there is nothing to configure for the signal itself — you only have to select the right transmitter.

The panel also decodes SSTV images from satellites that transmit them over an FM downlink. This is covered separately in Receive SSTV Images; the rest of this page describes telemetry frame decoding.

If the selected transmitter uses an unsupported modulation, or its parameters are unknown, the panel reports format not supported, and no decoding takes place.

Decoding a Pass

1. Open the Telemetry panel from the View / Telemetry menu.

2. Select the satellite in the Satellite Selector on the toolbar.

3. Select a data transmitter for that satellite. The decoder follows the transmitter selection, so pick the transmitter whose telemetry you want to decode. You can select it in the Satellite Transmitters panel, or by clicking on its label on the frequency scale. The panel header shows the satellite name and the selected transmitter; hover over it to see the resolved signal parameters.

   Many satellites have several transmitters on the same frequency, and only some of them may be supported by the decoder - for exmple, a CW beacon and a GMSK telemetry. The label you click on the frequency scale is not necessarily the one that gets selected, so after clicking check that the right transmitter is highlighted in the Satellite Transmitters panel.

   Some satellites can transmit their telemetry at different Baud rates, selected by the ground station. Such satellites have multiple transmitters in the database, one per Baud rate. To switch to a different rate, just select the right transmitter.

4. Make sure the SDR is running and tuned to the satellite. The decoder uses the same Doppler-corrected passband as the receiver, so the satellite's signal must be visible on the waterfall at the tuned frequency.

That is all that is needed to start decoding. When the satellite is above the horizon and a supported transmitter is selected, frames are decoded automatically and appear in the panel.

Layout

• The header at the top shows the selected satellite and transmitter. Hover over it to see the resolved signal parameters (modulation, baud rate, framing). The gear button to its right opens the Signal Details dialog.

• The status line below the header shows the current state of the decoder, in color:

  • satellite below horizon — the format is supported and the decoder is waiting for AOS; decoding starts when the satellite rises above the horizon;
  • ready to decode — the satellite is up and the decoder is listening;
  • DECODING... in green — a burst is being processed;
  • format not supported in red — the transmitter's modulation or framing is not supported;
  • terrestrial, not decoded in red — a terrestrial link is selected, which the decoder does not handle.

• The tree on the left lists the decoded passes and frames.

• The detail pane on the right shows the contents of the pass or frame selected in the tree.

Signal Details

For most satellites the signal parameters resolved from the database are correct and there is nothing to do here. Occasionally a transmitter is described incorrectly in the database, or its description is incomplete, and the decoder needs a hand. The gear button in the header opens the Signal Details dialog, which shows the parameters actually in use for the selected transmitter and lets you override any of them:

• Modulation and Framing — the modulation and framing format of the signal;
• Baud rate — the symbol rate;
• Deviation, Hz — the FSK deviation;
• AF carrier, Hz — the audio carrier frequency for AFSK downlinks;
• Manchester and Precoding (diff.) — the line coding and the differential precoding. These are tri-state: Auto leaves the decision to the decoder, On and Off force it;
• Telemetry format — the definition used to parse the decoded frames into named telemetry values. It is normally chosen from the satellite's NORAD number; select a different one here when the frames decode but their values do not. The field is empty, as in the picture above, when SkyRoof has no telemetry definition for the satellite — its frames are then shown without a PAYLOAD section.

To undo a single override, right-click the field and choose Reset to database value — the field goes back to the value the database gave it, leaving your other overrides in place. Cancel discards every edit you made since opening the dialog.

Click OK to apply your changes. A change to any of the demodulator fields rebuilds the decoder immediately, so it takes effect on the next burst. A change to the telemetry format applies to frames decoded from that point on and does not re-parse the frames already in the tree.

Overrides are remembered per transmitter for the current session only. They are discarded when you select a different transmitter, and they are not saved between runs.

Where a Value Came From

The dot to the right of each field shows where its value came from:

• no dot — the value from the satellite database, unchanged;
• orange — a value you edited that has not yet produced a frame;
• green — an override that has produced a valid frame, or a value the decoder itself discovered at run time (it locks the baud rate, deviation, and precoding as it decodes).

An orange dot that turns green is the confirmation that your override was right. One that stays orange means no frame has decoded with it yet.

The gear button's own color mirrors the dots, so you can see the state of the overrides without opening the dialog: gray when there is nothing to show, orange while an override is waiting for a confirming frame, and green once every override has produced one.

Passes and Frames

The frames are grouped by pass. Each top-level node in the tree is one pass of one transmitter, labeled with the start time, satellite name, and transmitter description. A pass node is created as soon as the first burst is detected and stays grayed out until the first valid frame is decoded.

Each child node is a single decoded frame, labeled with the time of arrival, the frame length in bytes, and, for AX.25 frames, the source and destination addresses. The newest pass is expanded automatically, and the view scrolls to follow new frames as long as the latest frame is selected.

Select a pass node to see a summary in the detail pane: the start time, satellite, transmitter, orbit number, the number of bursts, frames, and images decoded, and the signal parameters.

Select a frame node to see its full contents:

• TELEMETRY — the named telemetry values decoded from the frame (battery voltage, temperatures, and so on), shown only for satellites that SkyRoof has a telemetry definition for;
• ASCII — the frame bytes rendered as text;
• HEX — a hex dump of the frame bytes;
• META — the carrier frequency offset (CFO), signal-to-noise ratio (SNR), CRC check result, and the number of corrected bits and erased bytes from forward error correction.

Sharing the Frames

As each frame is decoded it is also, depending on the decoder settings:

• appended to a log file in the TelemetryDecodes subfolder of the data folder;
• sent to any client connected to the KISS-over-TCP server;
• uploaded to the SatNOGS DB.

Clearing the List

Right-click anywhere in the tree and choose Clear All to remove all passes and frames from the panel. This clears only the display; frames already saved to file or uploaded are not affected.