Tutorial ATSC

Tutorial: ATSC 1.0 (8-VSB)

What it is. ATSC 1.0 is the digital television standard of the United States, Canada, Mexico and South Korea. It uses 8-level vestigial sideband modulation (8-VSB) in a 6 MHz channel and carries an MPEG-2 transport stream with one or more services. In OnAir you tune a channel, the receiver locks its pilot and sync, and you watch the services in the TV tab. This is the older of the two ATSC standards; for NextGen TV see ATSC 3.0.

What you need

• A radio that samples at 8 Msps or faster: a 6 MHz channel does not fit an RTL-SDR (about 2.4 Msps). HackRF, Airspy, SDRplay, PlutoSDR, bladeRF, RX888 and similar work. See Supported radios.
• A TV antenna aimed at the transmitters (VHF-high and UHF). In most of the US the stations are on UHF.
• A frequency. The frequency database has the ATSC channel plan: channel 2 at 57 MHz, channel 3 at 63 MHz, channel 4 at 69 MHz, and so on in 6 MHz steps up to channel 36 at 605 MHz. The Band plan list on the Scan tab (pick your country) gives the ranges for your region.

Before you start

• Use a sample rate of 8 Msps. The synthetic test signal and recordings use the same rate.
• Do not overload the front end. Strong local stations are common in cities; if the signal looks flattened or the status bar shows overload, reduce the gain or use an attenuator. Auto-tune or Optimise gain finds a good level.
• 8-VSB has a pilot carrier at the lower edge of the channel; the receiver locks to that. A frequency error of several kHz is normal and is corrected.

Step by step

1. In the mode list open TV and choose ATSC (second line 8-VSB, North America).
2. Open the Scan tab, choose your Band plan, and press Start scan. The scan lists channels with state, services, SNR and load.
3. Pick a channel and press Start, or type a frequency in the top bar.
4. Wait for the status bar lamps Seg, Field and Eq (segment sync, field sync, equaliser) to go green.
5. Open the TV tab and click a service. Picture and sound start; the programme Guide is in the same tab where the broadcast provides one.

What you should see

• A rectangular spectrum 6 MHz wide with a small pilot spike at the lower edge.
• Lamps Seg, Field and Eq lit. On the Receiver tab (sub-view Sync): pilot carrier locked, carrier offset in Hz, symbol clock offset in ppm, segment sync with a correlation value, field sync, the equaliser state with the SNR measured from the known sync symbols, and the Reed-Solomon counts (clean, corrected, failed).
• A good signal shows very few failed Reed-Solomon packets; the corrected count is normal and just means the error correction is working.

Reading the screen

Tab	What it shows
Overview	Key plots and numbers.
TV	Player, service list, Guide, record, pause and live buffer.
Receiver	Sync, Signalling, FEC, Frame map, Channel.
Stream	Transport stream out (file, UDP/RTP, network tuner).
Scan	Channel scanner and the shared channel list.
Antenna	Direction finder for aiming the antenna.
History	The signal over time.

Options and settings worth knowing

• In Stream: remove null packets, record, stream to UDP (RTP if your player wants it) and share on the network.
• Fullscreen, pop out, on top, deinterlace, audio (track choice) in the TV tab.

Troubleshooting

• Pilot found but no field sync. Usually multipath or low SNR. Re-aim the antenna, try another position and watch the Channel sub-view.
• Locks and unlocks repeatedly. Check the lock-loss counter on the Sync sub-view. Reduce the gain if the signal is strong; otherwise raise it.
• Nothing found by the scanner. Confirm the radio really reaches the band (some radios stop at 1 GHz or have a gap) and that the sample rate is at least 8 Msps.
• Dropped samples in the status bar. The USB link or the computer cannot keep up; lower the rate if the channel still fits, or use a USB 3 port.
• A service lists but shows no picture. Check whether it is a subchannel with audio only, or encrypted. OnAir cannot decode scrambled services.

Tips

• ATSC subchannels (for example 4.1, 4.2) share one transport stream, so one lock gives you all of them.
• Used and checked on real broadcasts.

Legal and privacy notes

Receiving free-to-air broadcasts is legal in most countries. OnAir does not decode encrypted services and does not try to. See Legal.

Under the hood

ATSC A/53 uses 8-VSB at 10.76 Msymbol/s: a randomiser, Reed-Solomon (207,187), a convolutional byte interleaver and a rate 2/3 trellis code, with a pilot, segment sync (4 symbols) and field sync (every 313 segments). The receiver chain is matched filter, pilot loop, symbol clock, field sync, per-field equaliser, trellis decoding, de-interleaving and Reed-Solomon.

Related

Mode page: ATSC | ATSC 3.0 | DVB | Supported radios | Troubleshooting | FAQ