Hy-Gain 18 Instruction Manual

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General Description
Theory of Operation
Specifications
Choosing a Site
INSTRUCTION
MANUAL
ORDER NO. 386-A
Model 18 AVT/WB-A Vertical
Radiator, Amateur Antenna
PN 801270
The Hy-Gain 18AVT/WB-A is an omnidirectional, self-supporting, vertical radiator that
operates in the 10- to80-meter amateur bands. The system will work against earth ground
or a resonant radial system when mounted above ground. You make your own radial
system following the manual, or you can use the Hy-Gain 14RMQ radial system kit.
Performance of the antenna can be optimized for either phone or CW with either a ground
or roof mount. Regardless of the optimization, the VSWR bandwidths of the antenna are ,
broad enough for the antenna to operate at a VSWR of 2:1 or less from 10 to 40 meters.
The bandwidth for 80 meters'is sharper, because the antenna is top loaded.
Heavy-duty "Hy-Q Traps" give automatic band selection. The Hy-Q traps are parallel
resonant circuits which isolate the various sections of the antenna. This provides true
quarter-wavelength resonance on ail bands. The top hat and 80-meter resonator extends
coverage to 80 meter by top loading.
Mechanical
Overall: height 3... ota sees Sd oe eens eas da and Psa tl de 21' nominal (6.401 m)
Mast fact es teak crete eins at ei nok ke aaah eee, accepts up to 1%" (4.1 cm)
Wind survival ic. 3..0eed ce ie bel fais dale Laas ee Aa ee ls 80 mph (129 kmph)
Electrical
Frequency ..............002- 02 eee 80-, 40-, 20-, 15-, and 10-meter amateur bands
Input IMPEdance ... 6... eet eee eee ene n een es 52 ohms
SW at resonance: ioe kes fees eat Actin nla wae a intern less than 2:1
Power Capabilities 00... cece cent ene n eens 2 kW PEP*
Lightning protections ccs cies ia ea kinde ae elo wees now haa beat DC ground
INPUt. COMMECION 2.6 .8o ieee eta ban | oede Mae aada aes Picea ated os SO-239
"Maximum power on 80 meters is 1 kW PEP
NOTE: If the terminals of the input connector are checked with an ohmmeter, they will
show a direct short. This is normal! The matching coil in the antenna base puts the entire
system at DC ground, but presents a perfect 52-ohm impedance to RF energy.
A good ground is imperative for any vertical antenna system.
The 18AVT/WB-A can be mounted on the ground, on a rooftop, or on a mast. When
mounting the antenna above ground, remember that you must also install a ground plane
radial system. When the antenna is ground-mounted, a radial system is usually not
needed. But in some areas, where soil surface conductivity is poor and a good ground
cannot be made using the method shown in Figure 4, you will neéd to lay out ground
radials to improve the efficiency of your antenna.
If you mount your antenna on a roof and find the roof space is too small for a radial system,
you can droop the radials over the edge of the roof at almost any angle without seriously
changing the performance of the antenna. The radial system must be insulated from the
roof and connected to a good ground for lightning protection.
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