sceiv

Arv
Number 13 on your Feedback card
Ham Television
8ill Brown WB8ELK
do 73 Magazine
70 Route 202 North
Peterborough NH 03449
The NTSC ATV Repeater
Members of NTSC (the North Texas
Synchronization Society) in the Dallasfl.
Worth area have bullt a rather
unique ATV repeater system. Located
on a commercial TV lower (K TVT
channel 11) at the 1270-1001 level
(AG L), the coverage around the area
is tremendous. The NTSC group
chose an output on 421.25 MHz (horizontally
polarized) 10 make it easy for
those who had cable-ready TVs or
VCRs 10 lune in via cable channetS?
Since most 01 the commercial TV stations
are located near the NTSC site,
area residents with outside TV antennas
already have their antennas pointed
In thaI direction, As a resu lt. Its
very easy for ATV newcomers, Of
those cuneus about the mode, to tune
in to the action without having to buy
specialized downconverters or antennas.
A large viewing audience is possible
since there are several hundred
thousand people with horizontal TV
antennas and cable-ready TVs in the
region.
Doppler Rada r
The NTSC system has access to a
very fine Doppler radar system located
in Corsicana. This radar is owned and
operated by Weather Radar Waming
System, Inc. The Doppler radar system
is brought up during severe
weather and is used to look for storms
with tornado potential. Thanks to a
grant from me Tarrant County Firefighters
Association, NTSC was ab le
to purchase the equipment necessary
to bring the Corsicana radar output up
into the Dallas-Fl. Worth region. This
link consists of a TO systems CU·125
and a to-wen 915 MHz FM-TV transmitter
mounted in front of a Decibel
Prod ucts DB-495 comer renectcr antenna
at 60 feet. The link covers a 45­
nautical-mile path and is solid even
when the heaviest of storms pass
through the area. When not used for
weather radar, the 915 MHz FM-T V
frequency is used as the general user
input to the ATV repeater.
FM·TV Input
Since the input uses FM-TV. the
method of switching between the
weather radar and general purpose
users is rather unique. The repeater
receive antenna for the weather radar
Sell YOUR used gear
in 73 Classifieds. • .
Call Sue Colbert
1-800-274-7373
Micro Video Camera
Small size 1" x 2" x 3"
Light Weight < 4oz. Low!
Power 7 - 15 volts. @
85ma. Low Light @ 2 1
Lux. Camera comes com.'
plet in metal case with ,
RCA plug for video ou l .
and two plgtaled power
wires. Camera Is presently In use In RIC
airplanes. helicopters, cars, tanks and
rooots. Camera output Is .standard
NTSC at tv pop, 240 line resolution with
electronic Iris.
Full stock on hand.
Satisfaction Guaranteed!
Factory New, only $ 229.95 +$6
Sin For product information and
ordering. CallI (800)473-0538
MICRO VIDEO PRODUCTS
1334 So. Shawnee Dr. Santa Ana,
California. zip 92704 FAX (714) 545·K041
CIRCLE 30 ON RUOER SERVICE CARO
54 73 Amateur Radio Today. June, 1992
You
Can
Subscribe
to
73
by
phone.
Call
1-800­
289­
0388.
Photo A. The NTSC ATV repealer is situated at the 127(Hoot level of a commercial
TV lower near the Dallas-Fl. Worth area. Photo taken by Rabelt $kegg
VE7AII1W5 through a high-power lens.
is a vertieally polarized comer reflector.
The general user input antenna is
an 8-bay zig-za9 omni-direclional horizontal
antenna built by SIeve Fran klin
W85KG L , To change the leed between
general purpose users and the
weather radar, a touch-tone command
causes a relay to switch In one of the
antennas, The capture effect of FM­
TV allows the weather radar 10 run
continuously without interfering with
local users,
The Transm it Chain
The 421.25 MHz ATV transmitter
system consists Of a 2-watt exciter
built by Steve Fra nklin WB5KGL, A
Mirage D-100ATV, a 'r-pcle indigital fil-
ter buill by Artyn Stewart AA5BY, a
pair of cavities donated by Andy
Carstarphen WY5V and 45 feet of 112"
Heliax and connectors donated by
Merte Taylor WB5EPL
The antenna ertay (constructed by
Harold Reasnor K5SXKj consists of
four horizontally polarized dipoles
placed in a staggered arrangement
down the face of a 6-foot-long, 6' dtameter
secton of coaxial transmission
line donated by Sandy Sandberg
N5NBW. The staggered arrangement
of the dipoles achieves a cardioid type
pattern that favors the west, north and
south. This pattern was chosen to
avoid the possible mulfjpath effects of
the side-mounted antenna and to con-