TELE-TECH & - AmericanRadioHistory.Com

9
Antenna Arrays
(Continued from page 205)
magnitude evaluation is then made
and the array efficiency in field
strength computed and assigned as
previously.
Examples
(a) An array of two 60 radiators
spaced at 90 °. I;, = 1.0 /0 and I,,
0.9 / -150. The pattern shape is derived
from the above, and the RMS
value in reference units is 1.033.
From an impedance analysis it is
found that L, 8.31 a. and I,,
7.48 a., assuming a total power of
1 kw. Hence 1.033 is equivalent to
8.60 a.
A 60° radiator alone radiates 181
my -'m at one mile, has a base impedance
of 14 -- j 76, and thus a
base current of 8.45 a. for 1 kw.
Therefore the array RMs in field
strength is (8.60/8.45) x 181 = 184
my /m at one mile. See Fig. 1.
(b) An array of two 60° radiators
spaced at 210 °. I = 1.0 /0 and I -
0.9 / -10. The pattern shape is derived
and the RMS value in reference
units is 1.055.
From an impedance analysis it is
found that Ie = 7.21 a. and Il, _
6.49 a., assuming a power input to
the array of 1 kw. Hence 1.055 is
equivalent to 7.60 a.
As previously, the array RDAs in
field strength is (7.60/8.45) x 181 =
163 my /m at one mile. See Fig. 2.
(c) An array of two radiators A
= 90° and B = 60° and spaced at
210 °.I, = 1.0 LI and II, =0.9 / -10.
The pattern shape is derived and
the RMS value in reference units is
1.055.
From an impedance analysis it is
found that I, = 3.54 a. and II, = 6.61
a., assuming a power input to the
array of 1 kw. It is also found that
P° = 515 w. and P,, = 485 w. Since
A is 90° with an omni field of 190
my /m and B is 60° with an omni
field of 181 my /m, then Ea = 136
my /m for 515 w. and E1, = 126 my /m
for 485 w. The Rss for Ea and El,
combined is 185.5 my /m. This value
is equivalent to a 75° radiator with
a base impedance of 27.5 + j0 and a
base current of 6.03 a. for omni
operation.
Assume then that the array is of
two equivalent radiators 75° in
height and spaced at 210 °. The parameters
are as above and the RMS
value is 1.055.
From an impedance analysis (75°
radiators) it is found that L, = 5.17
(Continued on page 208)
lì
Quality- Minded Engineers
Specify
CONRAC MONITORS
Conrac Monitors are designed for continuous, trouble -free
service. Engineered to prevent costly repair bills, down time
and to save valuable man hours, Conrac Monitors are found
wherever exact monitoring is needed. You'll see them in use at
all of the major networks and a majority of stations.
Color Monitor CH 21 is a self -
contained picture monitor that can be operated
from NTSC encoded color video signals or
from simultaneous red, green and blue video
signals. It employs a three -gun tri -color picture
tube -type 2IAXP22. All operating and set up
controls, as well as o test po.nt for Y, 1, Q,
R, G and B, ore accessible from the front.
Schematic, engineering doto and specifications
fui nished on request.
Monochrome Monitors- Conrac manufac-
tures three monochrome monitors: the CB 17 -A,
a professional monitor of the highest quality
and the CF and CG Series general purpose
mon tors.
The CB 17 -A, designed for control room and
on -stage use, employs a 17" aluminized rectangular
picture tube. It may be rack mounted
in o standard 19" relay rack (No. CB 17A /R),
or furnished in utility heavy gauge steel cabinet
with carrying handles (No. CB I7A /C).
The CF and CG Series of video monitors are
general purpose monitors intended for broadcast
or industrial use. They present bright,
high definition pictures in continuous operation
with a minimum of maintenance.
The CF Series uses a 70° deflection system for
both 17" and 21" kinescopes. The CG Series
has a 90° deflection system for 24" and 27"
kinescopes. All chassis are supplied with picture
tube. The CF 17 is available for 19"
relay rock mounting, in a utility cabinet or
os a chassis. Model numbers ore os follows:
CF 17 -N CF chassis with 17" picture tube.
CF 17 -R CF chassis with 17" picture tube in
mounting for standard 19" relay rack.
CF 17 -C CF chassis with 17" picture tube in
steel housing equipped with carrying handles.
CF 21 -N CF chassis with 21" picture tube.
CF 21 -C CF chassis with 21" picture tube in
steel housing equipped with carrying handles.
CG 24 -N CG chassis with 24" picture tube.
CG 27 -N CG chassis with 27" picture tube.
Schematics, engineering dota and specifications
available upon request.
Audio -Video Tuner
The AV -12A is designed especially for re- broadcast applications -both
color and monochrome. It tunes any 12 channels. The AV -12A is ideal
for unattended operation because any one channel may be crystal
controlled, which prevents drift even under extreme conditions. Schematics,
engineering data and specifications furnished on request.
CONRAC, INC
S I N C E 1
3 9
GLENDORA, CALIFORNIA
Tele -Tech & ELECTRONIC INDUSTRIES June 1956 For product information, use inquiry cord on pages 209 -210. 207