I have had others interested in the 40-2CD design so I will repeat what I
also said to them.
The 40-2CD is a real toss up compromise design, BUT IT WORKS!
If you improve the unloaded Q of the coils, performance (mostly gain) will
increase slightly. However, at the same time, the bandwidth may decrease
since the losses in the loading coils will be less and losses can actually
The so-called capacity hats, the 36" rods just outboard from the inductors,
help to increase bandwidth. Removing them will force you to increase the
inductance of the loading coils or the length of the elements (or both) and
will probably decrease bandwidth.
I am not the designer of the 40-2CD although I was very familiar with the
design. The actual designer was the late Lester Cushman, ex W1BX. He did
some of the design at his home in his backyard. As the story goes from what
Lester told me, he was close to completion on the final design but needed
more test time.
One Dayton HamVention weekend I think in April 1982 (Lester didn't go to
HamVentions in his later years), he had the Cushcraft lab, equipment and
motorized tower to himself. He worked feverishly all weekend testing
different designs on the motorized tower and finally completed the design
on Sunday afternoon after 47 different crank up and crank downs just as the
motor failed! The following morning, when the normal design crew returned
for the HamVention, they were infuriated that the motor on the crankup
tower as burned out.....but now you know the rest of the story!
At 09:50 PM 2/16/2003 -0500, W0YR@aol.com wrote:
>Does anyone have experience with converting a 2 element Cushcraft 40 Meter
>yagi to a 3 el antenna. Did you buy/build the coils? Spacing that worked
>for u? Results?
>F/B Gain results? Bandwidth?
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