PAR OMNIANGLE OA-144 User manual

OMNIANGLE OA-144
2M HORIZONTALLY POLARIZED
OMNIDIRECTIONAL ANTENNA
PARTS LIST
PART NO. QTY DESCRIPTION
SUB14401 1 2 METER MATCHBOX
14402 2 3/4” SQUARE ALUMINUM RADIATOR
14403 2 3/16 ROUND ALUMINUM RODS
14404 1 FIBERGLASS ANGLE
14405 2 PLASTIC END CAPS
14406 1 BLACK PLASTIC TUBE
14407 1 ALUM. BACKUP PLATE
14408 2 S.S. 10-32X1 1/2” SCREW
14409 2 S.S. 1/4-20X2” HEX HEAD BOLT
14410 2 S.S. 1/4-20 HEX NUT
14411 2 S.S. 1/4” FLATWASHER
14412 1 5/8” X4” SQ. DIELECTRIC SPACER
14413 1 OA-144 INSTRUCTION SHEET
SUB14401
14407
FIG. 1
14402
14403
14406

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 (14402) and the dielectric spacer (14412). Refer to Fig. 3 and
Fig. 4. Insert the spacer into the the radiators and line up the holes. 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) 3/16” round rods (14403) and the black plastic tube (14406). Refer to Fig. 1.Note that
each radiator has a mark 4” in from one end. Push and twist the plastic tube onto the rod up to the 4”
mark. This is most easily accomplished by placing the rod in a vice with the 4” mark even with the
vice jaws. The jaws then act as a stop. Do the same with the remaining radiator. If you push the tube
too far, slide one of the 1/4” flatwashers onto the opposite end of the radiator and move the tube
back.
NOTE: Tolerances in the plastic tube sometimes makes it more difficult to insert the rods. The
task can be facilitated by starting the tubing onto a rod and then heating the tube with a
hairdryer. Push straight onto the rod to avoid kinking the plastic tube.
4. Refer to Fig 1. Insert one of the round ends into one of the holes at the end of the square radiators.
Insert the rod until 1” extends out the far side of the square radiator.
NOTE: If the antenna is to be mounted on a tower leg ,insert the radiators from the opposit side
shown in Fig. 1. This places the tower leg to the outside of the antenna triangle.
5. While holding the square radiator assembly carefully push the remaining 3/16” rod into the other
square radiator until 1” extends beyond the square radiator. Gentle flexing of the rod will be
necessary .
6. Refer to Fig 1 and Fig. 2. Assemble the back plate (14407) onto the 1/4” bolts with (2)
flatwashers (14411) 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 144.200 MHz is the most used frequency , tune the antenna to 144.4 MHz. This will
result in a match of perhaps 1.25:1 at 144.200 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 3/16” rods- Lengthening the
rods will lower the resonant frequency. To move a rod; hold the square radiator with one hand while
grasping one of the 3/16” rods close in to the square radiator. Flex the 3/16” rod to relieve pressure

Fig. 3
on the mounting hole. At the same time slide the rod in or out as required. When unflexed, the rod
will stay put.
Note: Be sure to lengthen or shorten the rods in equal increments.
3. Refer to the specification section of this manual for optimum stacking distance.
Fig. 2
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. Recent independent anechoic chamber
testing confirms the superior pattern and gain of this design over traditional loops.
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.

SPECIFICATIONS
Polarity: Horizontal
Pattern: Within +/- 0.8 dB omnidirectional
Design Z: 50 Ohms
V.S.W.R. Bandwidth: See Analyzer Plot
Power Handling: 160W
Weight: 1 lb
Size:. 14” X 18”
Materials: 6061-T6 Aluminum, Fiberglass
Suggested Stacking Distance 60”
Hardware: Stainless Steel
Connector: Silver/Teflon SO-239
V.S.W.R.
PAR ELECTRONICS
P.O. Box 645
Glenville, NC 28736
Voice: [phone]
FAX [phone]
E-Mail [email protected]