E2B: Television and SSTV

E2B covers amateur fast-scan television (ATV) and slow-scan television (SSTV): NTSC scanning standards, vestigial sideband modulation, digital television using DVB-T, SSTV color encoding, the Vertical Interval Signaling (VIS) code, and Digital Radio Mondiale (DRM) reception.

The Extra exam tests specific technical facts about how both analog and digital TV signals are structured, and how SSTV encodes image data in the audio frequency domain.

NTSC Fast-Scan Television

NTSC (National Television System Committee) is the analog fast-scan television standard used in North America. An NTSC television frame is composed of 525 horizontal lines. The frame rate is approximately 30 frames per second, with each frame divided into two fields at 60 fields per second.

The 525-line figure is a specific exam fact. The other choices — 30, 60, and 1080 — correspond to frame rate, field rate, and HDTV resolution, respectively. NTSC specifically uses 525 lines per frame.

Interlaced Scanning

NTSC uses an interlaced scanning pattern to increase apparent frame rate without doubling the bandwidth. In an interlaced system, each frame is divided into two fields:

This is not simultaneous scanning of two fields, not bottom-to-top scanning, and not alternating left-to-right with right-to-left directions. The defining characteristic is odd lines in one field and even lines in the next.

Vestigial Sideband Modulation

Vestigial sideband (VSB) modulation is a technique in which one complete sideband and only a portion (the "vestige") of the other sideband are transmitted. In analog TV, this means one full sideband carries the full video information, while a portion of the other sideband is retained to improve fidelity at low video frequencies.

The effect of vestigial sideband in analog fast-scan TV is to reduce the total bandwidth required while increasing the fidelity of low-frequency video components. The low-frequency components of a video signal — which carry large-area detail and slow luminance changes — benefit from the partial double-sideband transmission at low frequencies, giving better rendition of those components without requiring the full double-sideband bandwidth across the entire video spectrum.

Vestigial sideband does not carry audio, does not contain chroma information separately, and does not provide high-frequency sharpening. Its function is specifically bandwidth reduction with preserved low-frequency fidelity.

Digital Television: DVB-T

Amateur television operators can use the DVB-T (Digital Video Broadcasting — Terrestrial) standard for digital fast-scan TV. DVB-T uses two types of modulation:

DVB-T does not use FM, FSK, AM, or OOK. The combination of QAM and QPSK is the defining characteristic of DVB-T modulation.

Digital TV Coding Rate

In digital television, a coding rate of 3/4 means that for every 4 bits transmitted, 3 bits are actual data and 1 bit is forward error correction (FEC) data. Expressed differently: 25% of the total transmitted data is FEC overhead, and 75% is payload data.

The notation "3/4" represents the ratio of information bits to total bits — not data compression, not guard interval fraction, and not a word-length description. A higher coding rate (closer to 1) means less redundancy and more throughput; a lower coding rate means more redundancy and more error correction capability.

70-Centimeter ATV

A technique that allows commercial analog TV receivers to be used for amateur fast-scan TV on the 70-centimeter (440 MHz) band is transmitting on channels shared with cable TV. Cable TV uses the same channel frequency plan as over-the-air TV but distributed through coaxial cable. By transmitting on these cable channel frequencies at 70 cm, an unmodified cable-ready TV receiver can tune to the amateur ATV signal directly.

SSTV Color Encoding

In analog SSTV (Slow-Scan Television), color information is sent by transmitting color lines sequentially. The image is broken into its color components (typically red, green, and blue channels), and each color line for the full image width is sent one after another before moving to the next line. This sequential method is what distinguishes analog SSTV color encoding from other approaches.

SSTV does not use a 2.8 kHz subcarrier (that is a different digital mode parameter), does not send a color burst at the end of each line (that is an NTSC technique), and does not amplitude-modulate color onto the FM intensity signal.

SSTV Brightness and Line Sync

In analog slow-scan television, the brightness (luminance) of a picture element is encoded as a tone frequency — not tone amplitude. Brighter pixels correspond to higher audio frequencies within the SSTV audio signal; darker pixels correspond to lower frequencies. This frequency-modulated brightness encoding is the fundamental mechanism of all analog SSTV modes.

New picture lines are signaled to SSTV receiving software by specific tone frequencies. A sync tone at a defined frequency outside the normal image-data range tells the software to begin a new line. Timing alone is not used — the specific tone frequencies carry the synchronization information.

VIS Code

The Vertical Interval Signaling (VIS) code is a short digital code transmitted at the beginning of each SSTV image, during what would be the vertical blanking interval in conventional TV. The function of the VIS code is to identify the SSTV mode being used — it tells the receiving software which scan rate, color system, and synchronization format the transmitting station is using. Without the VIS code, the receiving software could not know which of the many SSTV modes (Martin, Scottie, Robot, etc.) to apply for decoding.

The VIS code does not lock the color burst oscillator, does not provide vertical synchronization timing, and does not transmit the operator's call sign.

DRM SSTV Reception

Digital Radio Mondiale (DRM) is a digital broadcast standard, but when DRM protocol is used for SSTV transmission, the receiver required is an SSB receiver. The DRM signal is demodulated as an SSB audio signal and then processed by software to decode the DRM-encoded image data. An SSB receiver provides the audio-frequency output that DRM decoding software requires; a dedicated CDMA, AREDN, or AM receiver is not appropriate for this application.

E2B Practice Questions