The LA1IC COAX-FED SLOPING LONGWIRE
Simple, inexpensive and easy to erect, this antenna
provides directivity, low angle radiation and a small gain on a number
of HF bands.
Primarily designed as a point-to-point DX-radiator
for 10, 12 and 15M, this antenna also does a fair job on 17, 20 and 30M.
Its total length of 41 meters (134.51 Feet ,velocity factor of
PVC-insulated wire included), is determined by the number of electrical
halfwaves on it: eight on 10M, seven on 12, six on 15, five on 17, four on
20 and three on 30M. Exactly 2.9 meters (the square root of 2.5 x 3.35m)
from the end of the wire we (the author & fellow antenna
experimenters) have found a good compromise 200 ohm feedpoint for the
three higher bands.
Using low power, and with an SWR meter inserted in the feedline, make readings across the 10, 12 and 15 meter bands. If the 38.1 meter section is too long, the lowest SWR will be at the LF end of the bands so that this wire should be pruned a little. At this stage it is best to just bend the unwanted wire, say 5 cm (1.9 inches) at a time, back on itself without actually cutting it, and the SWR measurements can be resumed. Several attempts at this ‘cut and try’ technique will result in a antenna which has a low SWR at midbands (typically 1:1.1) and which will not rise to no more than 1:1.2 at the band edges on 12 and 15, and 1:1.5 on the broad 10M band. When the correct length has been found the excess wire can then be cut and removed. With this setting the antenna will also work satisfactorily on 17, 20 and 30 meters, so do nothing more!
These plans submitted by Rolf Brevig, LA1IC
(Age 73 - licensed radio amateur since 1949,
originator of the "Coaxfeed 6 Meter Extended Double Zepp Zip Cord Antenna" on Hamuniverse.com!
Click here to see it.)
Many thanks Rolf! 73
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