[TowerTalk] add a 3rd el to 40-2cd

[Mpridesti]

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 at audiosystemsgroup.com> wrote:
> 
>> On 3/6/2018 1:57 PM, john at 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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