The Hy-Gain 18AVQII is an omni-directional, vertical radiator that operates on the 10, 15, 20, 40, and 80 meter amateur bands. The system will work against earth ground or a resonant radial system when mounted above ground. You can make your own radial system following the manual, or use the Hy-Gain RRK-88 Radial System Kit available at your Hy-Gain dealer.
The antenna can be used for either Phone or CW with either a ground or roof mount. It can also be tuned to mid-band for use with either Phone or CW.
In either case, the SWR bandwidths of the antenna are broad enough that the antenna will operate at an SWR of 2:1 or less on the 10, 15, 20 40 and 80- meter bands. The 18AVQII is supplied with stainless steel hardware and element clamps for all electrical and most mechanical connections.
Theory of Operation
The use of heavy duty "Hy-Q Traps" provides automatic band selection. The Hy-Q Traps are parallel resonant circuits that isolate the various sections of the antenna and give quarter wavelength
resonance on all bands. The top-loading coil is used for operation on the 80-meter band while the overall height of the antenna remains less than 20 feet.
WARNING: When installing your antenna, take extreme care to avoid any accidental contact with power
lines or overhead obstructions. Failure to exercise this care could result in serious or fatal injury
For maximum lightening protection we recommend the use of a lightening arrestor installed on the feedline along with a properly installed ground rod.
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.
However, it presents a 50-ohm load impedance to RF energy.
Choosing a Site
The 18AVQII can be mounted on the ground, on a rooftop, or on a mast. The antenna must be secured using non-conducting guy ropes. When choosing an installation site be sure to allow sufficient space for these guy ropes.
Radial System and Grounding
For best performance, the 18AVQII should be ground-mounted, clear of buildings and other structures. When the antenna is ground-mounted, a radial system is sometimes not needed. In most areas, where soil surface conductivity is poor and a good ground plane is not possible, lay out ground radials to improve the efficiency of your antenna.
When mounting the antenna more than three feet above ground, a resonant radial system must be used, such as Hy-Gain's RRK-88 Radial System Kit. If the antenna is roof mounted and 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.
Important: This antenna must be guyed for support. Non-conducting U-V proof guy rope (not included) should be secured between the tubing clamps (item #17) located below the 80-meter loading coil shown in Figure 2. The ends of the guys should be sufficiently anchored to the ground with stakes or another sturdy support.