In digital television, a coding rate of 3/4 refers to the ratio used in forward error correction (FEC), a method applied to ensure the reliability of data transmission. The coding rate is a fraction that represents the proportion of useful data in the transmitted signal. Specifically, a coding rate of 3/4 means that for every 4 bits transmitted, 3 bits are actual data, and 1 bit is used for error correction.

Last edited by berham. Register to edit

Tags: none

NTSC color encoding is used with the System M television signal, which consists of 29.97 interlaced frames of video per second. Each frame is composed of two fields, each consisting of 262.5 scan lines, for a total of 525 scan lines.

483 scan lines make up the visible raster. The remainder (the vertical blanking interval) allow for vertical synchronization and retrace.

The NTSC selected 525 scan lines as a compromise between RCA's 441-scan line standard (already being used by RCA's NBC TV network) and Philco's and DuMont's desire to increase the number of scan lines to between 605 and 800.

Source: Wikipedia

Last edited by perfect_disturbance. Register to edit

Tags: arrl chapter 8 arrl module 8e

Fast-scan television systems have two modes: progressive and interlaced. In progressive systems, the frame is scanned out completely, line-by-line. In interlaced systems, the odd-numbered lines are scanned out in one field, then the even-numbered lines are scanned out in the next field. When these two fields are interlaced back together, they make a complete picture.

Last edited by ka0s. Register to edit

Tags: arrl chapter 8 arrl module 8e

This question seems to exist to see if you will confuse fast-scan (or "normal") TV with slow-scan TV.

The easiest way to remember the answer is to remember that analog SSTV is pretty simple, so pick the simplest answer which is Color lines are sent sequentially.

From the Wikipedia page on SSTV:

A transmission consists of horizontal lines, scanned from left to right. The color components are sent separately one line after another. The color encoding and order of transmission can vary between modes. Most modes use an RGB color model; some modes are black-and-white, with only one channel being sent; other modes use a YC color model, which consists of luminance (Y) and chrominance (R–Y and B–Y). The modulating frequency changes between 1,500 and 2,300 Hz, corresponding to the intensity (brightness) of the color component. The modulation is analog, so even though the horizontal resolution is often defined as 256 or 320 pixels, they can be sampled using any rate. The image aspect ratio is conventionally 4:3. Lines usually end in a 1,200 Hz horizontal synchronization pulse of 5 milliseconds (after all color components of the line have been sent); in some modes, the synchronization pulse lies in the middle of the line.

Hint: SS in SSTV ... SS in "sent sequentially"

Last edited by tyrin. Register to edit

Tags: none

NTSC signals are amplitude modulated (AM) signals, but use a technique called vestigial sideband modulation. Vestigial sideband modulation is amplitude modulation in which one complete sideband and a portion of the other are transmitted. The reason that NTSC TV uses vestigial modulation is to conserve bandwidth. Even using this technique, an NTSC signal is 6 MHz wide. One advantage of using vestigial sideband for standard fast- scan TV transmissions is that vestigial sideband reduces bandwidth while allowing for simple video detector circuitry.

Hint: Only the correct answer has 2 "V"s in it "V"estigial and "V"ideo

Hint: Most of the answers on this exam that have to deal with bandwidth aim to reduce the amount of bandwidth used. This question is no exception. The only answer that mentions a reduction in bandwidth is the correct answer.

Last edited by senfo. Register to edit

Tags: arrl chapter 8 arrl module 8e

NTSC signals are amplitude modulated (AM) signals, but use a technique called vestigial sideband modulation. Vestigial sideband modulation is amplitude modulation in which one complete sideband and a portion of the other are transmitted. (E2B06) The reason that NTSC TV uses vestigial modulation is to conserve bandwidth. Even using this technique, an NTSC signal is 6 MHz wide. One advantage of using vestigial sideband for standard fast- scan TV transmissions is that vestigial sideband reduces bandwidth while allowing for simple video detector circuitry. (E2B05)

Hint: Vestigial means a small part or portion of something larger.

Last edited by wileyj2956. Register to edit

Tags: arrl chapter 8 arrl module 8e

QAM (Quadrature Amplitude Modulation) and QPSK (Quadrature Phase Shift Keying), as used in DVB-T (Digital Video Broadcasting - Terrestrial) for amateur television, are preferred over other forms of modulation due to several advantages.

1. Efficient Use of Spectrum: Both QAM and QPSK make efficient use of the available spectrum. They are capable of transmitting more bits per Hertz compared to simpler forms of modulation like AM (Amplitude Modulation) or FM (Frequency Modulation). This efficiency is crucial in environments where bandwidth is limited.

2. Robustness in Different Conditions: QPSK, being a phase modulation scheme, is particularly robust against signal degradation caused by noise and other disturbances. This makes it suitable for various transmission conditions, including those encountered in amateur television broadcasting.

3. Higher Data Rates: QAM, especially in its higher orders like 16QAM and 64QAM, can carry more bits per symbol compared to simpler modulation schemes. This allows for higher data rates, which is essential for transmitting high-quality video and audio content in digital television.

4. Compatibility with Digital Systems: Both QAM and QPSK are well-suited for digital transmission systems. They integrate seamlessly with other digital processing techniques, such as error correction and compression, which are integral parts of digital television broadcasting.

5. Flexibility and Adaptability: DVB-T allows for adaptability in transmission parameters, including modulation schemes, to suit different reception conditions. This flexibility ensures that the transmission can be optimized for different environments, from urban areas with high signal strength to rural areas where signals might be weaker.

6. Better Error Performance: With the incorporation of FEC (Forward Error Correction) and COFDM (Coded Orthogonal Frequency-Division Multiplexing), systems using QAM and QPSK can better handle bit errors due to noise or signal reflections. This results in a clearer and more consistent signal, which is vital for television broadcasting.

These advantages make QAM and QPSK highly suitable for the needs of digital television, particularly in amateur settings where efficient use of bandwidth and robustness against various transmission challenges are essential.

Last edited by berham. Register to edit

Tags: none

In the United States, the amateur 70cm band allocation is 420 to 450 MHz. It just so happens that US CATV frequencies for hyperband channels 57-61 (UU to YY) fall into this range.

Therefore, if you happen to have a CATV receiver, it is possible to connect it to an appropriate 70cm antenna instead of a CATV cable network and receive these amateur CATV transmissions over the air.

So Transmitting on channels shared with cable TV is the easiest way to fit fast-scan (regular video) TV transmissions into the amateur frequency allocations.

The other answers make no sense because: a satellite TV dish is made for a much higher microwave frequency and will not be helpful; transmitting on lowband VHF TV channel 2 (which is not really abandoned) is illegal with only an amateur license; and using USB modulation with a sound card lacks sufficient bandwidth for fast-scan TV (this is only used for SSTV).

More information is available here.

Last edited by ironcal67. Register to edit

Tags: none

SSTV (Slow Scan TV) is a digital mode used for sending still images to one another. This is done in the phone portion of the band using Single Side Band (SSB).

See the SSTV wiki for more info.

Hint: SSTV uses SSB

Last edited by liewo. Register to edit

Tags: none

The tone frequency of an amateur slow-scan television signal encodes the brightness of the picture.

SSTV (Slow Scan Television) uses analog frequency modulation, in which every different value of brightness in the image gets a different audio frequency. In other words, the signal frequency shifts up or down to designate brighter or darker pixels, respectively.

Color is achieved by sending the brightness of each color component (usually red, green and blue) separately. This signal can be fed into an SSB transmitter, which in part modulates the carrier signal.

Last edited by kt4obx. Register to edit

Tags: arrl chapter 8 arrl module 8e

Trick to remember: VIS CODE identifies MODE

From Wikipedia here https://en.wikipedia.org/wiki/Slow-scan_television

A calibration header is sent before the image. It consists of a 300-millisecond leader tone at 1900 Hz, a 10 ms break at 1200 Hz, another 300-millisecond leader tone at 1900 Hz, followed by a digital VIS (vertical interval signaling) code, identifying the transmission mode used. The VIS consists of bits of 30 milliseconds in length. The code starts with a start bit at 1200 Hz, followed by 7 data bits (LSB first; 1100 Hz for 1, 1300 Hz for 0). An even parity bit follows, then a stop bit at 1200 Hz. For example, the bits corresponding to the decimal numbers 44 or 32 imply that the mode is Martin M1, whereas the number 60 represents Scottie S1.

Vertical synchronization is not relevant, as slow-scan television only transmits one frame and so does not need a vertical sync component to start a new frame.

It is not for the call sign, as this is contained in the contents of the image that is sent.

Last edited by ky1ff. Register to edit

Tags: arrl chapter 8 arrl module 8e

SSTV (Slow Scan Television) transmits images by sending a series of audio tones. Each line of the image starts with a specific "sync pulse" tone (frequency), which tells the receiving software that a new line of the picture is beginning. This pulse ensures that the software can correctly align the image lines as they come in.

In summary, the receiving software detects these specific tones to synchronize and begin drawing each new picture line.

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 8 arrl module 8e