Hi,
I need some advice on a wire beam I built for field day and special
events. It has two fiberglass poles 22' long spaced 45' with a wire
Moxon for 40 M on the outside and a two element 20 meter beam between
the 40 meter Moxon. It has there is little interaction between the
beams either by model of by measurement. It is fed with two lengths
of RG-58 through 1:1 baluns at the antenna. I designed it using
EZNEC, and optimized it for gain with an eye on F/B ratio and
impedance. A few days ago I hosted it to 21' for a test. The design
was for 30' which will be the actual height in operation. I have a
chance to trim it before moving it to the special event location and
hoisting it to 30'. Measurement vs EZNEC values for Fo and Zo are as
follows at 21' and 30'.
Fo model: 7.26 MHz at 21', 7.19 MHz at 30'
Zo model: 41.85 Ohms at 21', 35.6 Ohms at 30'
Fo actual: 6.93 MHz, at 21'
Zo actual: 50 Ohms, at 21'
Fo model: 14.2 MHz at 21', 14.235 at 30'
Zo model: 35.2 Ohms at 21', 50 ohms at 30'
Fo actual: 13.99 MHz at 21'
Zo actual: 65 Ohms. at 21'
My question is, should I reduce the length of all wires in each beam
the % that the frequency is off in each beam and leave the spacing
alone, or should I reduce everything? It seems the frequency is off
because the model doesn't take into account all of the end effects,
but the spacing is not subject to end effects and should be left
alone. I have no way to measure accurately measure the elevation
angle, gain and F/B ratio.
The .ez files are available for the asking to individuals.
Tnx for your time.
Chs, W1CG
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