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VK2ZRG > TECH 09.01.05 07:45l 57 Lines 2417 Bytes #999 (0) @ WW
BID : 1036_VK2ZRG
Read: GUEST
Subj: Re: Stacking, Baying or Boxing Ant
Path: DB0FHN<DB0FOR<DB0MRW<DB0WUE<DK0WUE<SP7MGD<IZ0AWG<VK6ISP<VK2BNR<VK2TGB<
VK2IO<VK2WI
Sent: 050109/0508Z @:VK2WI.#SYD.NSW.AUS.OC #:58190 [SYDNEY] FBB7 $:1036_VK2ZRG
From: VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
To : TECH@WW
VK2ZRG/TPK 1.83d Msg #:1036 Date:09-01-05 Time:5:02Z
Hello Yagi stackers,
I've just read John's bulletin on antenna stacking. I
found the two `areas' that John mentions slightly confusing until I went back
and read it again. If the second `area' was stated as being in square degrees,
in the diagram, it would be clearer.
John wrote....
Aerial spacing, is variable, the manufacturers data may help, but a good guide
is about half the boom length for yagies & 2/3 boom length for QLY & ZLs. This
rule of thumb, makes sure the aerials capture areas (as if they were dish
aerials) do not overlap.
.....end of snip
Excuse my ignorance John; what is a QLY and a ZLs?
I can't agree with your rule of thumb guide of "half the boom length for
yagies" spacing. For some particular gain, this may be true, but it can't
apply to all boom lengths. Antenna gain, as most people would know, is the
ratio of capture areas of the reference antenna (dipole or isotropic) and
the subject antenna.
So doubling the capture area gives you a 3 dB gain. Most people know that
area is the product of two dimensions, e.g. height and width or length and
breadth. Increasing the two dimensions by a factor of 1.41 will double the
area.
So if the hypothetical Yagi had a correct spacing of half the boom length,
then doubling the boom length (which actually is a 2.5 db gain increase),
would require the spacing to be increased by 1.33 for 2.5 dB gain increase
(or 1.41 times for 3dB).
Here are some numbers from the ARRL Antenna Hand Book, 17th edition to
illustrate the point. For a 432 MHz Yagi
Stacking distance Ratio of E plane
Boom length Gain inches lambda spacing to
Lambda dBi E plane H plane E plane H plane boom length.
3.4 15.67 53 49 1.94 1.79 0.57
6.9 18.35 69 66 2.52 2.41 0.36
13.5 20.8 90 88 3.29 3.22 0.24
For lower gain (shorter) Yagis, the E plane space/boom length ratio is even
greater than 0.57. e.g. A 1.8 lambda boom length Yagi needs a 1.52 lambda
E plane spacing; a ratio of 0.84.
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
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