I built one using a longer DE (55 ft) and changed the 402CD elements to a
director (old DE) and the reflector. The boom used was 3 inch OD x 42 ft.
Had I stayed in my old QTH, was going to use two 402CD DE’s with the longer DE
and build a reversible 3 el. By adding a 7 ft stub on each parasitic element
and a relay to open/short the center, it would become reversible. Probably
would put it on a 48 ft boom to improve performance. Did start some prototype
work and was seeing 20 dB F/B.
Biggest negative is the low Q coils Cushcraft used. Was told that if I used
these coils on all 3 elements, gain would not be good so I opted to make a
bigger (closer to full size) DE and raise the Q of those coils. Overall it
seemed pretty effective although F/B was not that good - required more
tweaking.
Good luck but do consider a 2 el Moxon as a better choice.
Regards,
Mark, K1RX
> On Mar 6, 2018, at 5:24 PM, Jim Brown <jim@audiosystemsgroup.com> wrote:
>
>> On 3/6/2018 1:57 PM, john@kk9a.com wrote:
>> I have OptiBeam 40m antennas and when playing with a model, adding an
>> element really did very little. I do not recall the details but I think
>> some things like SWR bandwidth were even worse. You are probably better
>> off using the aluminum to make a Moxon
>
> I agree. In general, for an optimized design, gain in a Yagi is largely
> related to boom length. To benefit from a third element, it would probably be
> necessary to lengthen the boom. AND -- I wouldn't expect more than a dB or so
> for a build-able (and stay-up-able) antenna. :)
>
> 73, Jim K9YC
>
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