What is amateur TV?

        Presented by Amateur Television Network (www.atn-tv.org)

SECTIONS

1.   What is ATV       4.   Transmitters
2.   Operation         5.   Antennas
3.   Receivers         6.   Repeaters

Section 1: What is ATV?
Amateur Television (ATV) is divided into two primary types: Slow
Scan - a system used on the HF bands occupying the audio bandwidth
of an amateur station to transmit a few still pictures per minute
to another station usually over long distances and Fast Scan - a
system of sending broadcast quality full motion pictures over
shorter distances on the UHF and microwave bands.

In this presentation we will examine the Fast Scan version of ATV.
Back in the late 1940's hams in many parts of the country helped
develop commercial television. The old Amateur 5 meter band was
used for this mission. They were very helpful evaluating
reception of different system types and many engineers were also
hams using their vast technical knowledge for television
development. The hams - being hams - decided to build their own
stations. In the early days it was home brew or converted war
surplus UHF equipment.

By the 1960s home brew and converted UHF two-way radios were used.
By the 1970s technology changes were afoot with modulator and
downconverter kits and completed boards followed a few years later
by a complete ATV station in a box were available from PC
Electronics and other manufacturers. By the mid 1970s Metrovision
in Washington DC was the group that had built and licensed the
first ATV repeater in America. By 1979 WA6SVT had built the first
wide coverage repeater in California on top of Mt Wilson.
Over the years a group called Amateur TV Network (ATN) was formed
to support the repeater and many more repeaters soon followed.
ATN now has six state chapters across the country.

Today it is easier than ever to get on the air with ATV for less
than $700 for all new equipment and less than $100 for the
builder. The oldest and most widely used mode of ATV is AM and a
related modulation - Vestigial Sideband (VSB). A cable ready TV
set can directly pick up ATV on the 420 MHz band. A downconverter
is needed for the higher bands. Your camcorder can be used for
your ATV camera. All that is needed is a transmitter and antenna
and you are on the air!

FM ATV is one of the fastest growing modes of ATV. FM ATV uses 4
MHz deviation (the terrestrial commercial TV standard used for
studio to transmitter links and ENG) in the 0.9, 1.2, 2.4 GHz and
higher bands. A few ATVers use the satellite (TVRO) standard of
11 MHz on the 3.3 GHz and higher microwave bands. FM ATV using
converted part 15 TV room to room links - such as the WAVECOM
units - is available from ATV vendors. FM ATV is the preferred
mode in Europe on 1.2 and 2.4 GHz bands.

Digital ATV is just starting out by converting analog video to
MPEG-2 bit stream with QPSK, 8-VSB, and DVB modes of digital
modulation. Most of the research to date is done in Germany by
the DATV group using standard definition DTV on 434 MHz using
2 MHz of occupied bandwidth and HDTV on 1.2 GHz using 6 or 7 MHz
of bandwidth. In this country ATN has started experiments using
the methods above and using internet pipelines to link distant ATV
repeaters (see http://www.atn-tv.org) and look under ATN on the
internet for more details). The HSMM group is experimenting with
multimedia formats including ATV using 802.11b and WiFi part 15
equipment occupying 22 MHz in the 2.4 GHz band.

Section 2: Operation
ATV is unique in that it enables a ham to show and tell another
ham in real time his shack, latest project, field day, home video
of the family's vacation, and other events. ATV for public
service allows pictures in real time to be sent to emergency
operation centers to report storms and damage assessment.

Most ATVers use a 2 meter calling and coordination frequency to
set up ATV contacts. 144.34 MHz is popular in the Midwest and
some areas of the East Coast. 146.43 MHz is popular in the west.
Most ATV repeaters have a 2 meter receiver on site to mix in the
calling channel audio with the TV audio. On the 420 MHz band
polarization is usually vertical with areas that use 434 MHz and
horizontal in areas that use 439.25 MHz and areas with inband
421.25 MHz out and 439.25 MHz in repeaters. Most cross-band
repeaters use vertical polarization on both bands.

Lighting is important for good ATV pictures. More detail is
available in "Advancing the ATV Art Workshop" produced by ATN.
A camcorder, CCTV camera and most analog output computer cameras
work well for ATV. Antennas should be above the tree line for
good DX on simplex and operation to far off ATV repeaters.
Low loss feedline should be used. A low noise preamp is a good
idea if you use a cable ready TV or an older downconverter.
At least 10 watts is needed for good ATV distance and 100 watts or
more for long haul DX work.

ATVQ magazine (http://www.atvquarterly.com) is a good resource for
information on what is happening in your area on ATV, projects you
can build, ATV group information and advertising for the latest
ATV gadgets for sale by reputable ATV vendors and manufacturers.

Section 3: Receivers
The simplest ATV receiver for AM or VSB is the standard TV set
using a 6 MHz wide channel. A cable ready TV can receive the 420
MHz band ATV signals - just add an antenna (and preamp for even
better performance) and you are ready to receive ATV! For a non-
cable ready TV add a downconverter and for the higher bands a
downconverter is needed for all TV sets.

FM ATV needs a TV with A/V inputs or a video monitor, both
requiring a full FM TV receiver. Low cost Part 15 domestic units
work well on 2.4 GHz and imported Part 15 type units work well for
1.2 GHz or 2.4 GHz bands. A satellite receiver can work on 0.9
and 1.2 GHz bands for FM TV but are set up for wideband FMTV and
need a preamp and filter for better operation. They work well for
Wideband ATV with a downconverter on the 3.3 GHz band and above.

Section 4: Transmitters
It used to be said that AM TV on the 420 MHz band was the easiest
way to get on ATV and that is still probably true but the Part 15
FM TV units are also simple to use on 2.4 GHz. Most ATVers use
off the shelf transmitters or a transmitter with a built in
downconverter. Transmitters use crystal control or PLL to set
frequency and AM modulate the carrier directly with video.
Audio is modulated on a 4.5 MHz subcarrier and mixed in at the
video modulator. The transmitter is double sideband occupying
9 MHz. The easiest way to build a VSB ATV transmitter is to
either add an external RF 6 MHz wide bandpass filter to your
existing AM transmitter or use a CATV Modulator.

CATV modulators are rack mountable and are much more
sophisticated. They modulate a 45.75 MHz IF with video then
filtered though a VSB 5 MHz wide IF filter. The audio is
modulated on a 41.25 MHz carrier at 25 KHz deviation. Usually the
aural carrier is phase locked to the visual carrier maintaining a
precise 4.5 MHz difference. The aural and visual carriers are
mixed to the final output frequency and amplified. Most CATV
modulators can produce an output to 550 MHz making them suitable
for the 420 MHz band. The modulator output is in the 10 to 20 m/w
level requiring amplification with a class AB RF power module.

The easiest FM ATV transmitter is a Part 15 TV unit on 2.4 GHz.
The frequency chip can be changed to put all four channels into
the ham band on coordinated ATV frequencies. Amplifiers are
available from ATV vendors. Imported Part 15 type TV units for
1.2 GHz band are available from ATV vendors.

Section 5: Antennas
The antenna system and its placement is one of the most important
items in designing any ham station. In ATV we need more signal as
compared with voice modes due to our larger bandwidth.
Base stations should use a directional 13 dbd or better gain
antenna to get as much signal as possible and to reduce co-channel
QRM and multipath. The polarization is dependent on what is used
in your area. Stacking yagis or using larger microwave dish
antennas will give better DX on ATV.

The best location for your antenna is above the roof line and
trees. Stay away from RG-58, RG-8 and other HF-VHF feedlines.
They have too much loss at UHF and even more on microwave.
The same goes for the PL-259 connector. Use type N or other
quality connectors. LMR-400, 9913 and heliax are preferred
feedlines for ATV. Try to keep losses under 3 dB. Waveguide is
used for the 5 and 10 GHz bands. DX can reach 50 to 100 miles
with good antenna systems and several hundred miles with tropo
ducting. KH6HME's ATV transmission from Hawaii was received by
ATV stations 2500 miles away in California in full color with
tropo ducting.

Section 6: Repeaters
ATV repeaters are fast becoming popular for ATV activity.
Today many hams are finding themselves in antenna restricted
communities reducing simplex ATV to about 10 miles but an ATV
repeater on a high tower or mountain top allows longer distant ATV
contacts. Many ATV groups and individuals have built ATV
repeaters. ATN has a linked network of interstate repeaters
allowing ATV contacts over hundreds of miles.

The two types of repeaters are:

Inband where both the input and output are in the same band
(popular in the Midwest since existing ATV simplex stations do not
require additional equipment to use the repeater) and

Cross band repeaters have the input and output in different bands
allowing the sending station to see his own picture, make
adjustments to his station and hear distant stations talk back to
him over the repeater via the ATV 2 meter calling channel audio
mixed at the repeater. A separate antenna and downconverter or
transmitter is needed compared to simplex operation.

The Microwave Experimental Television Society (METS) uses a
wideband FM input on 10.4 GHz using Gunplexers to transmit and
slightly modified domestic C band satellite receivers to receive
their 3.4 GHz wideband FM TV repeater output.

ATV repeaters are located in a high centrally located area and use
omnidirectional antennas. The repeater's transmitter is keyed up
upon detection of horizontal sync on the repeater receiver. ID is
usually done visually by momentary interruption of the received
ATV signal by an ID screen or done via video overlay.
Some repeaters have two inputs: one is the old 420 MHz channel and
the 2nd is a 2.4 GHz FM TV channel.

MPEG-2 Motion Picture Engineering Group's broadcast digital video
    standard
DVB   European HDTV and DTV standard
QPSK  Quadature Phase Shift Keying
8-VSB  8 Level digital Vestigial Sideband, the US HDTV and DTV
    standard