I had been thinking about this array since I saw it on the cover of CQ,
and was wondering what it would look like on ELNEC. So after seeing some
of the postings here on the refelctor, I spent some time today at lunch
modeling it in ELNEC V3.04.
WX7M's array was at a low height of 50 ft or .72 WL at 14.2MHz. Since I
already had a 10 meter 6 element yagi modeled, I chose to extend it out
to 16 elements (130 ft boom) and analyzed it at 25 ft. or .72 WL at
28.4MHz. This design was for a direct 50 ohm feed; therefore, it may not
reflect the maximum gain available when using another feed method (i.e.,
gamma, beta, T, etc.).
Assuming I have not made any mistakes (I'm still a novice at this
modeling stuff), here is what I found ----
16 element yagi at .72 WL:
Gain -- 17.998 dBi at 13 degrees takeoff angle, Secondary lobe -- 6.347
dBi at 60 degrees, F/B -- 20.075, -3dB beamwidth -- 26 degrees, Impedance
-- 50.08 +J 10.13, SWR (50ohm) -- 1.224
At 1 WL the gain increased to 18.789 at 11 degrees, S-lobe gain of 10.163
at 42 degrees.
At 1.5 WL the gain increased to 19.984 at 9 degrees with a lot of minor
lobes.
As a comparison, the orginal 6 element yagi design ( with a boom of 34
ft.) had a gain of 15.5 at 13 degrees at 1 WL height.
The question thus becomes, what other ways can you achieve these kind of
gains? Stacking two or more smaller (as in manageable and affordable)
yagis should come reasonably close to these same figures. Has anyone
modeled KC1XX's arrays (eight Cushcraft 104CDs)? Someone mentioned
curtain arrays. Well, a stacked pair of extended double Zepps (EDZ) with
resonate refelctors will provide similar gains. See the ARRL Antenna
Compendium Vol. 5 for an example, or check out L.B. Cebik's web page for
articles on EDZs. One 10 meter model I have provides 17.89 dBi at 10
degrees, -3dB beamwidth of 38 degrees, with the bottom wires at one WL
and the upper wires at 1.625 WL. And if you add resonant directors, the
gain goes up another 0.5 dB.
Anyhow, hope this was of interest to someone. And yes, it would be great
if CQ or the next Antenna Compendium had an article on this or a similar
large yagi array.
73,
Henry Pollock - WB4HFL
Raleigh, NC
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