Figure A Six-element Yagi Beam for 6 Meterr This antenna desagned by Wl JR proiddes a power gain of 10.2 dB over a dipole It is built on a 24 foot long boom).
The parasitrc elements are lnsulated from the boom by small phenolic blocks hetd to the boom with U-bolts. The driven element is attached to the bopm dlreetly The length of the driveri.element may be adjusted to aehleve torvest SWt; after the initial adjustments are made to the tength of the gamma matching rod Gain of this dessgn drops off qt,ta quickly on the high side of the desrgn frequency but much more slowly. on the low-frequency side Plan vtew of the entenna is shown. in A and details of the gamma mazching section are shown at B.
Figure B L-P Yagi Antenna for six Meters c This design combines bandwidth of log-periodic strudure with gain of Yagi antenna. L-P Yagi may be built on h" (4.0 i cm) diameter boom, about 19' (5.8 m) long. L-P elements are insulated from boom by mounting on insulating blocks. Yagi elements are grounded to boom at their center point. The antenna is fed with a balanced 70-ohm ribbon line at the feedpoint and the L-P transmission line is made up of No. 8 aluminum clothesline wire, criss-cross conneded between the elements.. Rear element is shorted with 6" loop of aluminum wire. The spacing between the inner tips of the L-P elements is 3.5" (8.9 cm).
Figure C The J-Pole Antenna for 50 and 144 MHz The half-wave
vertical antenna is a popular omnidirec- tional installation for the vhf bands.
A-50 MHz J-pole antenna. The coaxial cable is brought up inside the aluminum
pipe, which serves as antenna and mast. The outer shield of the line is grounded
to the pipe 6" above the mounting clamp for the matching sedion. The inner
condurtor is tapped on the matching sedion as shown. B-144 MHz J-pole antenna. A
coaxial receptacle is mounted on the shorting bar. The inner terminal is
tapped on the vertical radiator through a 20-pf variable capacitor. Adjustment
of the capacitor and the tap point (about 2" above the bar) permit a very low
value of SWR to be achieved on the transmission line. This is a simple version
of the gamma match.