Tutorial MAC

Tutorial: MAC (D2-MAC and D-MAC satellite TV)

What it is. D2-MAC and D-MAC were the hybrid analogue-digital satellite television systems of the late 1980s and 1990s, used for example in Scandinavia, France and Germany. The picture is sent as time-compressed analogue video lines and the sound and data as a digital burst, all on one FM-modulated carrier about 27 MHz wide. Few such transmissions remain, so this mode is mostly for recordings and historical interest. OnAir finds the line sync, decodes the picture, the channel name, the digital sound and the format (4:3 or 16:9), and detects EuroCrypt without descrambling it.

What you need

• A radio that samples at 16 Msps or more (the mode asks for 20 Msps, which sees most of the 27 MHz channel). HackRF, Airspy, PlutoSDR, bladeRF and similar. See Supported radios.
• A dish and LNB, as for DVB-S/S2, if you want to receive a live signal. The radio sees the LNB's IF; the default start frequency is 1200 MHz and the mode table covers 50 to 6000 MHz. This mode has no frequency database entries; take the transponder from a satellite list and subtract your LNB oscillator.
• Or, much more likely, a recording. See Signal samples.

Before you start

• Tune the centre of the FM channel.
• Gain: the LNB output is strong; keep the radio from overloading. The status line shows the input level.
• Not supported: B-MAC and C-MAC (the app says so).

Step by step

1. In the mode list open TV and choose MAC (second line D2-MAC, D-MAC satellite).
2. Open a recording (file source) or connect the radio and press Start at the IF of the channel.
3. Open the Video tab. The panel on the left (CHANNEL) lists the channel name and network as soon as the data arrives.
4. Watch the state: searching, line sync, frame sync and decoding.

What you should see

• A wide FM carrier about 27 MHz across.
• The Video tab shows the picture and the Line (baseband) and Data burst eye plots. A healthy eye is open.
• Readouts, grouped as Signal (state, system variant, data SNR, video SNR, offset, deviation in MHz/V, whether the spectrum is normal or inverted and corrected, input rate and level), Sync (line rate in Hz and ppm error, line sync quality, frame sync words found and frames, frame count, bit errors), Service (channel and network name), Packets and Sound.

Reading the screen

• Line (baseband): one video line with its time-compressed chrominance and luminance halves.
• Data burst eye: the duobinary data burst; open means a low bit error rate.
• EuroCrypt is reported when the conditional access is detected; the service is not descrambled.
• 16:9 marks widescreen services.

Options and settings

• The test signal can generate a clean D2-MAC or D-MAC signal with options for EuroCrypt, 16:9, C/N, offset and a picture to check the chain.
• Spectrum inversion (from some LNBs) is corrected automatically.

Troubleshooting

• No line sync. Wrong frequency, too narrow a sample rate (use the 20 Msps setting) or a weak signal.
• Picture without sound. The digital sound packets need frame sync; check the frame sync counts and bit errors.
• Scrambled picture. EuroCrypt or another conditional access: not descrambled.
• B-MAC / C-MAC. Not decoded.

Tips

• Recordings of real MAC signals are very welcome.
• The frequency database has no MAC entries; do not expect a live signal in most regions today.

Legal and privacy notes

Receiving free-to-air broadcasts is legal in most countries. Encrypted MAC services are detected, not descrambled.

Under the hood

MAC (ETSI/EBU specifications for the MAC/packet family): the 625-line picture is sent as separate time-compressed luminance and chrominance in each line period, followed by a digital burst (duobinary, about 20 Mbit/s for D-MAC and half that for D2-MAC) that carries sound, data and the service identification; the whole baseband frequency-modulates the carrier. The receiver demodulates the FM, finds line and frame sync words and reassembles the packets.

Related

Mode page: MAC | DVB-S/S2 | Analog TV | Signal samples | Supported radios