omniangle oa-222 - PAR Electronics

OMNIANGLE
OA-222
1.25M HORIZONTALLY POLARIZED
OMNIDIRECTIONAL ANTENNA
PARTS LIST
PART NO.
QTY DESCRIPTION
SUB22201
22202
22203
SUB22202
14404
14405
14406
14407
14408
14409
14417
14410
14411
14418
14412
22213
1
1
1
2
1
2
2
1
2
2
2
2
2
2
1
1
1.25 METER MATCHBOX
3/4” SQUARE RADIATOR LEFT
3/4” SQUARE RADIATOR RIGHT
1/4” ALUMINUM ROD ASS’Y
FIBERGLASS ANGLE
PLASTIC END CAPS
4-40x3/8” STAINLESS SCREW
ALUM. BACKUP PLATE
S.S. 10-32X1 1/2” SCREW
S.S. 1/4-20X2” HEX HEAD BOLT
#10 S.S. SPLIT RING LOCKWASHER
S.S. 1/4-20 HEX NUT
S.S. 1/4” FLATWASHER
S.S.1/4” SPLIT RING LOCKWASHER
5/8” X4” SQ. DIELECTRIC SPACER
OA-222 INSTRUCTION SHEET
202
B22
SU
SUB22201
222
02
FIG. 1
3
20
22
ASSEMBLY
1. Refer to Fig. 2 . Select the fiberglass angle (14404) and the (2) 2 ” hex head bolts (14409). Insert
the bolts through the 1/4” holes in the direction shown.
NOTE: The supplied bolts are satisfactory for support masts up to 1 1/4” diameter. Substitute 2 1/2”
stainless bolts for a larger mast up to 1 1/2”.
2. Locate the (2) 3/4” square radiators (22202) and the dielectric spacer (14412). Refer to Fig. 3 and
Fig. 4. Insert the spacer into the the radiators and line up the holes. Place #10 lockwashers onto each
#10 screw.Use the (2) 10-32 screws to join the radiators, angle and matchbox in that order. Tighten
the screws in equal steps. Screws should turn in easily. Securely tighten the screws but avoid
overtightening.
3. Locate (2) 12”X1/4” rod assemblies (SUB22202). Refer to Fig. 1. Loosen the (2) 4-40 screws
that are at the ends of the square radiators enough to allow the rods to pass through. Insert the rods
from the same side the matchbox is on. Allow approximately 5/8” of 1/4” rod to extend out the back
side. Lightly tighten each screw just enough to hold the rods in place.
4. Refer to Fig 1 and Fig. 4. Assemble the back plate (14407) onto the 1/4” bolts with (2)
flatwashers (14411), (2) lockwashers (14418) and (2) 1/4-20 hex nuts (14410). Slip the backup plate
over the support mast and tighten the nuts equally. As you tighten, adjust the antenna and backup
plate square to the mast. Do not overtighten, this will only warp the fiberglass angle and backup
plate.
TUNEUP
1. Mount the antenna in the clear. If mobile mounting, try to mount the antenna 20” or more above
the vehicle roof. This will ensure maximum gain close to the horizon and an impedance match close
to that of free space. Connect an antenna analyzer, VHF V.S.W.R. bridge or VHF wattmeter through
a short length of coaxial cable. If using a transmitter, we suggest using low power for tuneup until
you get the antenna adjusted.
Note: All horizontal omni antennas we are familiar with tend to detune when subjected to rain or
even foggy conditions. Those tested became unusable under these conditions because of high
V.S.W.R. The Omniangles have virtually eliminated this problem by virtue of their wide bandwidth
and plastic coatings. However, a small amount of detuning may still occur. We suggest that the
antenna be tuned 200 to 300 KHz above the normal operating frequency. As an example, if
operation at 222.100 MHz is the most used frequency , tune the antenna to 222.4 MHz. This will
result in a match of perhaps 1.25:1 at 222.100 MHz.- this will not affect antenna performance and
will allow wet weather use with a low V.S.W.R.
2. The resonant frequency is adjusted by lengthening or shortening the 1/4” rods- Lengthening the
rods will lower the resonant frequency. Lightly tighten the 4-40 screws after each adjustment.
Note: Be sure to lengthen or shorten the rods in equal increments. We suggest moving in 1/16”
increments.
3. When tuning is complete, tighten the 4-40 screws 1/4 turn after you feel the screw contact the 1/4”
rod assembly.
HOW THE ANTENNA WORKS
Halo or loop antennas attempt to achieve an omni pattern by shortening a half wave dipole and
forming it into a loop. Resonance is restored by capacity loading the far ends of the loop. The intent is
to equally distribute current throughout the length of the antenna. Still, the current diminishes towards
the end resulting in an egg shaped pattern. The other side effect of shortening is a severe reduction in
usable bandwidth and a susceptibility to detuning with rain.
The Omniangle antennas are approximately 30% longer than a half wave. It is this electrical length in
combination with the isosceles triangle shape that yields a near perfect omnidirectional pattern, much
wider bandwidth, and considerably less rain detuning.
Because the antenna is longer than a half wave, it is no longer resonant. The matchbox efficiently
converts the feedpoint impedance (approximately 10 +J90 Ohms) to 50 Ohms resistive. Finally, a
teflon current mode balun ensures equal current to both sides of the antenna.
Fig. 2
Fig. 3
Fig. 4
V.S.W.R.
SPECIFICATIONS
Polarity:
Pattern:
Design Z:
V.S.W.R. Bandwidth:
Power Handling:
Weight:
Size:.
Materials:
Suggested Stacking Distance
Hardware:
Connector:
Horizontal
Within +/- 0.8 dB omnidirectional
50 Ohms
See Analyzer Plot
160W
1 lb
8” X 12”
6061-T6 Aluminum, Fiberglass
36”
Stainless Steel
Silver/Teflon SO-239
PAR ELECTRONICS
P.O. Box 645
Glenville, NC 28736
Voice: (828)743-1338
FAX (828)743-1219
E-Mail par@parelectronics.com