Tutorial Analog TV

Tutorial: Analog TV (PAL, SECAM, NTSC)

What it is. Analogue television is switched off in most countries, but it still lives on cable networks, in test equipment, in CCTV and drone video links (FPV), and in vintage and hobby setups (including NBTV and mechanical television). OnAir finds the vision carrier, detects the line standard and the colour system, and shows the picture with its FM sound.

What you need

• A radio that samples at 8 Msps or more (the mode asks for 10 Msps). See Supported radios.
• An antenna for the band you are interested in, or a direct feed (a modulator, a camera transmitter, a cable). The mode table covers 45 to 6000 MHz; the default start frequency is 600 MHz.
• Systems covered: B/G, I, D/K, M, N, H, K', positive-modulation A (405 lines), C, E (819 lines), L, L', plus NBTV and mechanical TV. Modulation choices: AM (broadcast), FM video (FPV), and NBTV / mechanical in AM or FM.
• A frequency: this mode has no entries in the frequency database. For terrestrial broadcast use your national channel plan; for FPV use the video-link frequency of your equipment (5.8 GHz and 1.2 GHz are named in the app's help).

Before you start

• Tune the centre of the channel: the vision carrier is found by itself. NICAM and two-carrier sound are not decoded; the FM sound carrier is.
• Do not overload the radio; the sync tips flatten and the picture loses contrast.
• Interference from digital TV on neighbouring channels is common; a good channel filter in front of the radio helps.

Step by step

1. In the mode list open TV and choose Analog TV (second line PAL, SECAM, NTSC).
2. In the tuner (left, section CHANNEL) set Modulation: AM for broadcast TV, FM video for FPV. Leave System on automatic; pick the system by hand only if detection is wrong. Leave Colour on automatic too.
3. Type the frequency and press Start.
4. Open the Video tab. The picture builds up as the receiver locks to line and field sync.

What you should see

• A vision carrier with a sound carrier above it in the spectrum.
• The Video tab shows the picture; the controls under it include Weave and Bob (two ways of putting the two interlaced fields together; Weave for still pictures, Bob for motion), Colour, Envelope detector, Saturation and Tint.
• The status block reads: state (searching, carrier and line sync, locked, decoding), system, colour system (with a note when the colour burst is too weak), raster (lines and field rate), detector (synchronous or envelope), the vision and sound carriers in MHz, SNR and the line and field sync quality.

Reading the screen

• Line (composite): one line of video as a waveform: sync tip, back porch with the colour burst, picture. Use it to judge levels and noise.
• Standard block: system, colour system, raster.
• Carriers: vision and sound frequencies.
• FM video block (in FM mode): which end of the frequency range the sync tip is on, and the video SNR. Sound is not decoded in FM video mode.

Options and settings

• Modulation: AM (broadcast), FM video (FPV), NBTV / mechanical (AM or FM). In NBTV mode you also get Lines, Pictures/s and a NBTV 32 preset (the 32-line standard).
• Envelope detector: switches from the synchronous detector to a simple envelope detector; try it on a weak or distorted signal.
• The test signal can generate any of the supported systems with C/N, carrier offset, hum, ghost echoes and sync compression.

Troubleshooting

• Picture rolls or tears. Weak signal or wrong system. Choose the system by hand.
• Black and white only. The colour burst is too weak (the status says so) or the colour system is wrong; set Colour by hand or raise the SNR.
• Inverted picture. Positive and negative modulation standards differ (A, C, E, L are positive modulation); pick the right system.
• No sound. The sound carrier may be NICAM or a second carrier; only the FM carrier is decoded.
• Nothing at all. Check the frequency and the sample rate; analogue channels are 6 to 8 MHz wide.

Tips

• Checked with generated signals and impairments; recordings of real signals are welcome.
• A recording of a VHS tape player's RF output is a good test source.

Legal and privacy notes

Receiving broadcasts is legal in most countries. Some places restrict receiving drone video links or private video transmissions; check your local rules.

Under the hood

Vision carrier with vestigial sideband (VSB-AM, negative modulation in most standards), FM sound carrier at 4.5 to 6.5 MHz above it depending on the system, composite video with line and field sync, PAL/NTSC colour subcarrier phase or SECAM FM colour. FPV video links use FM video.

Related

Mode page: Analog TV | MAC | Spectrum explorer | Supported radios | Troubleshooting