As planned, I installed the 40-2CD on Saturday morning with the
shortened reflector tips (about 2.57 inches less than the CW dimension
listed in the manual). The antenna has exactly the SWR curve (measured
at the antenna) predicted by EZNEC, which means, for one thing, that the
coil losses I used in the model are in the ballpark. I have not done
enough testing to verify the F/B ratio, as the band has been quite noisy
the past few nights. The antenna certainly has a lot of gain compared to
just the driven element. I need to recruit a local to provide a signal
source, then measure the F/B across the band the *correct* way (with the
AGC off and a calibrated step attenuator in line).
As LB Cebik has observed, there are pitfalls in modeling antennas like
the 40-2CD. This is not an easy antenna to verify or optimize with the
software tools commonly available to amateurs. However, from the SWR
curve correlation, I have at least some confidence that I've achieved
the desired result; the longer-term performance tests will tell the rest
of the story.
A couple of people have noted that a 40-2CD tuned for the CW part of the
band has lousy performance in the SSB segment. If you've also had this
or related experiences, please post them to the reflector.
--73, Rus, NJ2L
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