The use of fiberglass for the manufacture of collinear VHF antennas. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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The use of fiberglass for the manufacture of collinear VHF antennas and "square" spacers is a common phenomenon. Often, fishing rods are used for these purposes, which at the end of the season are not so expensive compared to duralumin pipes (non-ferrous metal!). In addition, the rods have a good "action" in terms of bending mechanics, since, in addition to being telescopic, there is also a slight taper.
I propose (maybe my idea is not original) to use them as carriers for Yagi-type HF antennas. Inside these fiberglass tubes should be placed duralumin (copper) wire, which is, in fact, the shoulder of the vibrator, director or reflector. Since the conductive element is thin, its required length will be close to the calculated one. In addition, the influence of the boom and the need to adjust for its influence will be greatly reduced, since the elements are isolated.
According to a reasonable remark by Viktor Pronin (UA4HBW), the latter circumstance makes it possible to implement LOG-YAGI type antennas with less problems, where it is necessary to isolate the elements from the boom. The antenna elements are protected from the weather. Antenna tuning can be carried out using ordinary side cutters by simply biting off the wire.
To reduce the influence of the dielectric (fiberglass) on the parameters of the antenna and eliminate mechanical rattle, the vibrators are fixed in several places inside the tubes with foam rubber "washers" (pieces of foam rubber) - as in collinear antennas. The antenna turns out to be light and strong and does not need additional extensions from the boom side, which, as a rule, need to be broken with insulators (bends, but does not break). It becomes easier to implement a Yagi type antenna for 40 and even 80 meters (there are long rods!).
Of course, in industrial conditions, the design of the tubes can be specially designed.
Literature
- HF and VHF radio amateur, 3/2001
Publication: N. Bolshakov, rf.atnn.ru
See other articles Section HF antennas.
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