At 01:04 PM 6/26/2009, Dennis wrote:
>Of course I need this antenna to work for Field Day so Murphy Strikes again
>at the worst possible time ! )
In my personal experience, the dimensional control of the shorting
bars for the EF-240 is so loose that it is unlikely dimensions from
one installation will work at another, even at exactly the same
height. There's also the question of how taut or loose the linear
loading wires are, in case you want to add another variable.
What I did here was to feed a weak signal source - my MFJ259B -to 3
feet of wire about 300 feet from my EF-240S, using an RX antenna
feedline. Then I changed the frequency of the MFJ and turned the
antenna until I experimentally found the frequency of maximum F/B
ratio. My first time around, it was too high, and by moving the MFJ
to the bottom of the band I could determine that the pattern of the
antenna actually reversed, as the reflector turned into a
director. It took two adjustments to get maximum F/B at around 7025,
but that's where it wound up, and I'm quite satisfied with the pattern.
If you have a way of tilting the antenna down so you can get to the
reflector shorting bars, I'm convinced this works better and takes
less fussing than the "cookbook" method.
73, Pete N4ZR
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