Tutorial DVB S S2

Tutorial: DVB-S, DVB-S2 and DVB-S2X (satellite TV)

What it is. DVB-S, DVB-S2 and DVB-S2X are the satellite television standards. You receive them with a dish and an LNB (the block at the dish's focus), and the radio sees the LNB's output, the intermediate frequency (IF) in the L-band, not the 10 to 12 GHz signal itself. OnAir measures the carrier, finds the symbol rate and the MODCOD, decodes the stream and plays the services in the TV tab. It is also useful for amateur DATV on QO-100 (see QO-100).

What you need

• A satellite dish aimed at your satellite and an LNB. A standard Universal LNB converts 10.7 to 11.7 GHz with an oscillator at 9750 MHz and 11.7 to 12.75 GHz at 10600 MHz. The IF is the downlink frequency minus the oscillator. Example from the app's own help: a transponder at 11.727 GHz vertical lies at 11727 - 9750 = 1977 MHz IF.
• A power supply for the LNB. The LNB needs about 13 V (vertical) or 18 V (horizontal), plus a 22 kHz tone for the high band. OnAir cannot switch this itself: the radio's bias-tee gives only about 5 V. Use a power inserter, a satellite finder or a switch. The tuner has an LNB supply setting so OnAir can warn you if the transponder and the LNB polarisation do not match.
• A radio that reaches the IF (950 to 2150 MHz for a Universal LNB). The mode accepts a sample rate of 2 Msps and up and asks for 10 Msps. A HackRF sees about 17 MHz at 20 Msps, which is a carrier of up to about 15 Msym/s. Wide transponders (27.5 Msym/s and more) do not fit; use a wider radio or a recording.
• A DC block in line with the radio's input if the LNB power inserter does not already give one.

Before you start

• Satellites have narrow beams; aiming the dish is the hardest part. Use a satellite finder and a published transponder list.
• Gain: LNB output is strong. Start low and use Auto-tune or Optimise gain.
• The default start frequency is 1500 MHz (the middle of the IF band); type the IF of the transponder you want.

Step by step

1. Aim the dish, connect the LNB to the radio through the power inserter and DC block, and power the LNB.
2. In the mode list open TV and choose DVB-S/S2 (second line Satellite).
3. In the tuner, set Symbol rate to Auto (measured from the carrier width) or untick Auto and type the rate in Msym/s. Set Standard to Auto, DVB-S only or DVB-S2 only. Optionally set Transponder (the polarisation you want) and LNB supply (what your LNB is switched to).
4. Type the IF frequency and press Start. A flat-topped block should appear in the spectrum.
5. Watch the lamps in the status bar: Carrier, Timing, Framing, FEC, TS lock.
6. Open the TV tab and pick a service.

What you should see

• A flat-topped carrier with sloping edges (the roll-off). Its width in Msym/s is shown as the symbol rate.
• Readouts: state, standard, symbol rate, mode (the MODCOD, e.g. QPSK 3/4 or 8PSK 2/3), Es/N0, margin, carrier offset, frames, Reed-Solomon (DVB-S) and packets. Margin is measured against the ideal-demodulator Es/N0 of EN 302 307-1 table 13, so a real receiver needs a little more.

Reading the screen

• The lamps run in order: carrier found, timing locked, frame sync, FEC decoded, transport stream locked.
• NOTES at the bottom of the receiver panel explain what the receiver sees. After ten seconds with no carrier it tells you: most often the LNB is on the other polarisation (13 V vertical, 18 V horizontal) or the other band (22 kHz tone), or the dish is off target.
• DVB-S2X: the MODCODs of EN 302 307-2 table 17a and the very-low-SNR frames of table 18a (set 1 and 2) are decoded; the low roll-offs 0.15, 0.10 and 0.05 are followed. Superframes (Annex E) and bundled channels are not decoded.

Options and settings

• Compute (CPU, GPU, Auto): where the LDPC (DVB-S2) and Viterbi (DVB-S) decoders run. The stream is the same either way.
• Stream tab: record, UDP/RTP, network tuner.
• The test signal has controls for standard, modulation, rate, symbol rate, roll-off, short frames, pilots, inverted spectrum, Es/N0 and carrier offset.
• The Spectrum explorer has a button Open in DVB-S/S2 that fills in the frequency and symbol rate of a carrier you picked there (see Spectrum explorer).

Troubleshooting

• No carrier. Check LNB power, polarisation and band, then aiming. Use the spectrum to look for the transponder first.
• Carrier, no timing. The symbol rate is off. Set Auto or type the right rate; very low rates need a narrow filter.
• Timing, no FEC. Es/N0 too low (small dish, rain, wrong polarisation skew) or the standard hint is wrong. Try DVB-S2 only or DVB-S only.
• TS locks but no picture. The service is encrypted. OnAir does not decode scrambled services.
• Everything is mirrored. Some LNBs and converters invert the spectrum; the inverted option in the test signal shows what that looks like; the receiver handles inverted signals.

Tips

• Start with a strong, wide-known transponder to confirm the chain works, then try weaker ones.
• Checked with generated signals and impairments; recordings of real signals are welcome.

Legal and privacy notes

Receiving free-to-air broadcasts is legal in most countries. OnAir cannot decode encrypted services and does not try to. Check local rules for dishes on buildings.

Under the hood

DVB-S (ETSI EN 300 421): QPSK, Reed-Solomon (204,188), convolutional interleaving and a punctured convolutional code. DVB-S2 (ETSI EN 302 307-1): QPSK, 8PSK, 16APSK and 32APSK, LDPC with BCH, physical-layer framing (PLHEADER, pilots), roll-offs 0.35, 0.25, 0.20. DVB-S2X (EN 302 307-2) adds more MODCODs and lower roll-offs.

Related

Mode page: DVB-S/S2 | QO-100 | Spectrum explorer | DVB | Supported radios | Troubleshooting