Thanks to all for the leads on this question. In going back to my ARRL
antenna Book, and borrowing a newer edition, I find that the 4-element
Quasi-LPDA should work, and if it ismade into a 5-element array, it
becomes (almost) a "true LPDA"...
One of the things pointed out is either called a "Design Constant" or the
"Slope". This is the arbitraily-picked number, smaller than 1.0, that
one multiplies (or divides) the lengths and the resonances to generate
the periocity(???) in the array. If you caluculate out the ratios
between the center frequencies in the 17, 15, 12 and 10 Meter band, they
all fall at 0.86, plus/minus 0.02. This is close enough for me. The
spacings between elements is not as clear, falling between 0.05-wave and
0.10-wave, with the longer arrays having more gain, but being bulkier.
Here's what I came up with, on paper:
1st element - Fr = 15.53 MHz, L = 30.14 ft
2nd element - Fr = 18.06 MHz, L = 25.91 ft
3rd element - Fr = 21.00 MHz, L = 22.29 ft
4th element - Fr = 24.41 MHz, L = 19.17 ft
5th element - Fr = 28.39 MHz, L = 16.48 ft
L1 - L2 = 3.17 ft
L2 - L3 = 2.72 ft
L3 - L4 = 2.34 ft
L4 - L5 = 2.02 ft
Boomlength = 10.25 ft
Approximate gain (and, this is from some very hard-to-read charts) ~6.5
dBi
If the charts are correct, with the smallish "Active-Cell" size, the
QLPDA would show about1.5 - 2 dB less gain than a 2-element yagi for the
band, but would cover all 4 of the upper bands at an SWR of <2:1, this on
a single feedline.
As soon as the WX allows, I am going to try one, and will post my
findings.
72/73, Keith, WB2VUO, QRP-L #582, scQRP 40, Tech Specialist (ARRL/WNY),
ARRL Life Member, VP/BARK, Beacon Chaircritter, Rochester VHF Group
Trustee, KB2YTW/B 10 Mtr QRPp Beacon (250 mW @ 28.2870 MHz)
"In the Depths of the Great Bergen (NY) Swamp...FN13ac"
Packet - wb2vuo@w2im.#wny.ny.usa.noam
Email - wb2vuo@juno.com
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