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2016 Extra Class study guide: E2B - Amateur television

Posted: 18 Mar 2016 07:24 AM PDT
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E2B- Television practices: fast scan television standards and techniques;
slow scan television standards and techniques

Although we are called “radio� amateurs, we can also transmit and receive
television signals. There are several ways that amateurs communicate by
television. Perhaps the two most popular ways are standard fast-scan
television and slow-scan television (SSTV).

The video standard used by North American Fast Scan ATV stations is called
NTSC.(E2B16) The NTSC, or National Television Systems Committee, is the
body that set standards for the analog television system that was used in
the U.S. and many other parts of the world. After nearly 70 years of using
the analog NTSC system, U.S. broadcasters switched over to a digital
broadcasting system on June 12, 2009.

A fast-scan (NTSC) television frame has 525 horizontal lines (E2B02), and a
new frame is transmitted 30 times per second in a fast-scan (NTSC)
television system. (E2B01) NTSC systems use an interlaced scanning pattern.
An interlaced scanning pattern is generated in a fast-scan (NTSC)
television system by scanning odd numbered lines in one field and even
numbered ones in the next. (E2B03)

In order for the scanning beam to only show the picture, a technique called
blanking is used. Blanking in a video signal is turning off the scanning
beam while it is traveling from right to left or from bottom to top. (E2B04)

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)

Amateurs can transmit color TV as well as black-and-white TV. The name of
the signal component that carries color information in NTSC video is
chroma. (E2B07)

There are a number of different ways to transmit audio with an NTSC signal.
The following are common methods of transmitting accompanying audio with
amateur fast-scan television:

Frequency-modulated sub-carrier

A separate VHF or UHF audio link

Frequency modulation of the video carrier

All of these choices are correct. (E2B08)

Because of the bandwidth requirements, amateurs can only transmit fast-scan
TV above 440 MHz. FM ATV transmissions, for example, are likely to be found
on 1255 MHz. (E2B18) In fact, one special operating frequency restriction
imposed on slow scan TV transmissions is that they are restricted to phone
band segments and their bandwidth can be no greater than that of a voice
signal of the same modulation type. (E2B19) The approximate bandwidth of a
slow-scan TV signal is 3 kHz. (E2B17)

SSTV images are typically transmitted on the HF bands by varying tone
frequencies representing the video are transmitted using single sideband.
(E2B12) The tone frequency of an amateur slow-scan television signal
encodes the brightness of the picture. (E2B14)

128 or 256 lines are commonly used in each frame on an amateur slow-scan
color television picture. (E2B13) Specific tone frequencies signal SSTV
receiving equipment to begin a new picture line. (E2B15)

There are a number of different SSTV modes. The function of the Vertical
Interval Signaling (VIS) code transmitted as part of an SSTV transmission
is to identify the SSTV mode being used. (E2B11)

Digital Radio Mondiale is one way to send and receive SSTV signals. No
other hardware is needed, other than a receiver with SSB capability and a
suitable computer, is needed to decode SSTV using Digital Radio Mondiale
(DRM). (E2B09) Just like any SSTV transmission, 3 KHz is an acceptable
bandwidth for Digital Radio Mondiale (DRM) based voice or SSTV digital
transmissions made on the HF amateur bands. (E2B10)

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