On Sun, 9 Dec 2001 "Jim" <w7ry@earthlink.net> writes:
>
> Perhaps I should just put up my 204BA ? Do you think that
> a longer boom is worth the effort with 4 elements ?
>
Look at the Gain vs. Boom Length Curves in the W2PV
Yagi Antenna Design Book, figure 2.12 on page 2-23.
Then study the gain and F/B graphs for 4L equal spaced
designs with equal length directors earlier in chapter 2.
The gain curve is NOT linear, but rises rapidly from 0.1 to 0.4 WL
which is the usual range for 2 and 3 elements, then rises more
SLOWLY from .4 to .6 WL which is the usual range for 4L
(and short boom 5L) designs, then rises more rapidly again
from 0.6 to 0.8 WL, which is the usual range for 5 or 6L Yagi
designs, and again levels off from 0.8 to 1.1 WL.
For 20M, a 3 or 4L Yagi on a 24 to 28 ft boom provides good gain
and pattern. To obtain 2 more dB gain, one needs to go to 5L
on a 56 ft boom. Intermediate boom lengths with 4L might yield
an additional 1 dB over a wide spaced 3L but F/B is typically poor
unless the end director is made unusually short such as the CC
Skywalker series antennas which are a good example of this
approach. Gain is roughly equal to 3L optimized for gain but
F/B equal to 3L optimized for F/B.
The HG 204BA is a VERY GOOD design on a 24 (26?) ft boom
with the advantage that it has a wide opening in the middle which
makes is a good candidate for stacking / side mounting.
Tom N4KG
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