Thursday, March 3, 2011

Quarter-wave vertical antenna for VHF


Quarter-wave vertical antennas are useful for local communications when size, cost and ease of  construction are important.

The antennas shown are built on a coaxial connector. Use UHF or N connectors for the fixed station antennas. BNC connectors are good for mobile and portable antennas. BNC
and N connectors are better than PL-259 connectors for VHF/UHF outdoor use because: (1) they provide a constant impedance over the frequencies of interest, and

(2) they are weatherproof when the appro priate connector or cap is attached. The ground-plane antennas require a panel-mount connector (it hasmounting holes to hold the radials).
If the antenna is sheltered from weather, copper wire is sufficiently rigid for the element and radials.

Antennas exposed to the weather should be made from 1/16- to 1/8-inch brass or stainless-steel rod.Radials may be made from 3/16-inch aluminum rod or tubing and mounted on an aluminum sheet. Do not use aluminum for the antenna elementbecause it cannot be easily soldered to the coaxial-connector center pin.Where the figures call for #4-40 hardware, stainless steel or brass is best. Use cadmium plated hardware if stainless steel or brass is not available.


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