I read the papers N6RK mentioned, and think i understand what they're saying
about matching and losses.
KU7G's article in the July, 1984 QST "Limitations to Broadband Impedance
Matching" ends with
"The original goal put forth by Hall [network at antenna feed point to produce
reasonable impedance match over the entire 80m band] does not appear practical.
The Fano Limit tells us that we will not obtain a match over the entire
band with a traditional dipole. As Hall suggested, the answer probably lies
other antenna forms. Specifically, we need antennas with significantly reduced
to obtain a match over a 500-kHz bandwidth, even with special networks"
On page 7-27 of the 20th ed ARRL Antenna Book, where these antennas are called
"coupled resonators", they say the antennas are easily simulated with NEC. They
call out the special problem of the 80/75 antenna, because the driven element
element has low impedance at the higher frequency. What's different, is they
wide spacing is needed..i.e. 3 to 4 feet.
Mine has 6".
I did look again at the currents in the two elements, base on N6RK's feedback.
Both elements do have similar currents. This (I**2 R) seems to decrease
efficiency relative to a simple dipole?
I did look at the efficiency numbers 4nec2x was reporting.
Ignoring the feedline loss, with copper conductors, it reports efficiency is
at 3.9Mhz, and at 3.6Mhz.
Using ARRL TLW separately to look at feedline loss with RG-6, I'm only
.4db or so loss in the matching section.
Compared to a number of other broadband solutions for 80m in the ARRL antenna
book with <90% efficiency at the band edges, I'm thinking this is all
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