WHAT CAN YOU PUT ON ATV?
Any Technician class or higher radio amateur can transmit
ATV to other amateurs on amateur frequencies above 420
MHz, and Novices on 1270-1295 MHz. Besides showing you
and your gear in the shack, you can show and describe your
latest projects in detail, copy schematics, help debug
computer programs, put on your own home video tapes and
movies, computer graphics & games, repeat Space Shuttle
video from the NASA Select satellite channel, repeat SSTV,
RTTY, Packet, etc. to ATV. You can repeat computer
generated weather radar or satellite video for skywarn and
emergency amateur radio groups. Transmit the local radio
club meeting to those that physically can’t make it. Virtually
any non-commercial video from your camera, VCR or NTSC
compatible computer is simply plugged into the video in jack
and sent exactly as you would see it on the local monitor.
ATV is a big help for getting an overview of an operational
situation during parades, races, search and rescue, major
fires, and other disasters. Public service is a great way to
have fun with your ATV gear. Your transmissions must be
controlled by licensed hams, and directed primarily to another
ham. ATV has been used for public service in vehicles,
portable, boats, airplanes and helicopters. For portable, the
TC70-20 can be carried in a knap-sack, a short coax run to
a 1/4 wave ground plane clipped onto a headset/mic, and
plugged into a 6 Amp/hr gel cell battery. The OAL 5L-70cm
beam is only 31” long, 8 dB gain and its >60 degree
beamwidth cuts down the multipath ghost problem from
reflected RF coming in from the sides and back at the receive
site. 2 Radio Shack 5 ft mast sections and tripod fit easily in
the car with the beam for portable operations.
If used in an aircraft for fun or remote damage assessment
with emergency service groups or CAP, run RG400 (available
at businesses that do cellular telephone installation in cars)
or RG142 coax instead of RG58 coax to the antenna.
Ordinary coax will put noise in the picture due to vibration
modulation - there is enough attenuation change as the ohmic
contact between adjacent strands of the coax shield rub back
and forth. Use only a stiff quarter-wave spike on the bottom
of the aircraft to minimize radiation nulls as the plane banks
- do not use gain antennas. FAA certified antennas for the
amateur bands are available from Comant (562) 946-6694.
Snow free line of sight DX with the quarter wave on the belly
to a 9-10 dB omni (F718) on the ground is 25 miles.
WHAT CAN’T YOU DO WITH ATV?
All the FCC rules and regs in part 97 apply (47 CFR). The
ARRL FCC Rule Book is a good reference that explains all
these by practical examples. All amateur transmissions must
be directed to another amateur with few exceptions for con-
trol, tests or emergencies (97.111, 97.215, 97.401 to 97.405).
Therefore ATV cannot be used for surveillance purposes for
personal, business or law enforcement. You cannot “broad-
cast” (97.113) to a non-amateur or retransmit any other radio
service (except Space Shuttle Video and audio) or music.
ATV cannot be used as a cheap link for local cable or public
access community TV systems, church services, video or
movie production directly or indirectly. Basically you cannot
use Amateur radio to further any business purpose, profit or
non-profit or activity contrary to Federal, State, or local law .
There are other frequencies and licensing for these purposes.
LIGHTS, CAMERA, ACTION.
Proper lighting makes a big difference in picture contrast
quality. It is best to have a light at, or just behind, the camera
directed at the subject to remove shadows caused by the usual
overhead lights. Do not crank up the video gain control to
bring up dark areas as the bright areas will over modulate
giving sync buzz, instability and may splatter the band.
With color cameras, try to use only one type of lighting...do
not mix sun light through a window, incandescent and
florescent lamps with each other or the colors will shift as you
swing the camera. Set the color camera white balance every
time you first turn on the camera by aiming at an all white
sheet illuminated by the same type of light in the scenes you
will be showing. For outdoors, especially public service events,
CCD or MOS cameras are preferred over vidicon types as
they will not normally be damaged if accidentally aimed at
the sun.
Since a picture is worth a thousand words, you will note
that you will run out of subject matter faster than voice modes.
So the more people you can get on ATV, the greater the things
to show. Pick an ATV net night and publicize it at your local
radio club by having them include the time, video and 2 meter
talkback frequency in the club newsletter. Better yet start off
by giving them a talk/demo. Once they see their first picture
they are usually hooked - this can be as simple as connecting
an outside 440 MHz antenna of the same polarity you are
using to a cable ready TV set to cable channel 57 through 60
- these cable channels correspond to frequencies between
421.25 to 439.25 MHz and are different than over the air
broadcast channels. To keep the net interesting vary each
net night of the month with a theme: everybody has to show
a family member, a project, wear a hat, make a new call ID
sign, a pet, 1-2 minute personal video tape, etc. - ENJOY!
For more general or background information on ATV check
out page 12.46 in the 1995-2000 ARRL Handbook and
Amateur Television Quarterly Magazine. There are also ATV
remailers on the internet - contact us at: [email protected]
for the latest internet addresses and ATV repeater group web
pages. Our web site: www.hamtv.com
STATION IDENTIFICATION.
You must identify with your call letters every 10 minutes
and at the end of every transmission (97.119). This can be
done by voice on the sound subcarrier or by call letters on the
screen. If done on video, the letters must be large enough to
be easily seen in the picture. Many just put up a large call
sign with black letters on white board on the shack wall in
normal camera view. You can get fancy by overlaying your
call letters over the camera video with a GVID board in the
video line, or computer generated special effects. In weak
signal conditions, it has been found that large, fat black letters
on a white background which fill the whole screen show up
best in the snow. Others use a computer and switch between
the camera and a generated graphic call sign.
Teachers who are licensed radio Amateurs can transmit to
another amateur, classroom to classroom, or to other schools
as long as it is used to demonstrate Amateur radio or radio
communications or for fun between school radio clubs. They
cannot, however, transmit normal lessons, broadcast school
sporting events or other school business.
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(c) 2000 P. C. Electronics