Subj : Stacking, Baying or Boxing Ant
To   : WW
From : G8MNY
Date : Wed Aug 28 2019 11:02 pm

G8MNY    TECH     28.08.19 11:05l 103 Lines 4517 Bytes #365 (0) @ WW
BID : 19216_GB7CIP
Subj: Stacking, Baying or Boxing Ant
Path: OK0NBR SR8BBS SR6DWH SR6BBC SR9ZAA VE2PKT N3HYM GB7YEW N9PMO JE7YGF 
      GB7CIP
Sent: 190828/1342Z @:GB7CIP.#32.GBR.EURO #:19216 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                                 (Updated Dec 05)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
AERIAL SPACING
Aerial spacing figures are variable depending on what books you read etc, the
manufacturers data may help if it is based on real measurements. But without
any other information a good guide is about half the boom length for normal
Yagi aerials up to 4 wavelengths long. Longer aerials can be stacked closer.

Stacking formula to fit some data looks like this...
                   ______________________ 
Boom length       û Boom Wavelengths -1.13
Stacking     =    ----------------------
Fraction                  0.86

Use 2/3 of the boom length (or of the formula above) for the higher gain
aerials like Quad loops, loops, HB9 & ZLs.

This ONLY a rule of thumb as the relationship to length, gain & capture area is
not linear.
                                            ______
AERIAL CAPTURE AREAS     ______            /      \
          ______        /      \          ³        ³
BAD OVER /      \      ³        ³         ³        ³ WASTEFUL
LAPPING ³ _ _ _  ³     ³        ³          \______/  MAST
        ³/      \³      \______/  IDEAL              SPACING
   GAIN ³\_ _ _ /³      /      \   NO       ______    NO
   LOSS ³        ³     ³        ³ GAIN     /      \  GAIN
         \______/      ³        ³ LOSS    ³        ³ LOSS
                        \______/          ³        ³
                                           \______/

Makes sure that the aerial capture areas (as if they were dish aerials) do not
overlap.

    Gain
+3dB Ä´                          _..... Nearly +3dB
+2dB Ä´               ,/'\._ _./'
+1dB Ä´     ./'\     /      "
 0dB _³_.,/'    `-.-'
     ÄÅÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄ  Spacing
  Touching   Too      Close    Half Boom
            Close    Optimum    Length

Closer stacking or baying, gives variable results as all the aerial elements
will couple, & this will result in a different polar diagram & gains less than
optimum. But closely mounted aerials with high gains are possible, if difficult
to get the distance just right & for just one spot frequency!

STACKING, BAYING or BOXING AERIALS
The aim of using more aerials is to improve performance by reducing aerial beam
lobe size (Beam angle) to increase the gain.
     ___                                       __
   /'   `\              ______               /'  `\                __
 /' Front `\         ./'      `\.           ³  «   ³            ./'  `\.
³   Beam    ³        ³  « Area  ³           ³ Area ³            ³¬ Area³
 \  Area   /         `\.______./'           ³      ³            `\.__./'
  `\.___./'                                  \.__./
  1 Aerial         2 Aerials Stacked     2 Aerials Bayed     4 Aerials Boxed
 Gain/one 0dB          up to 3dB            up to 3dB           up to 6dB

From these plots you can see that aerial Stacking offers gain without the
reduction of horizon beamwidth, or reduction of contact opportunity. With 2
Bayed aerials or 4 Boxed aerials with its nice 6dB gain, there is loss of
contact opportunity if Dx stations are not around on that beam heading.

Another point often forgotten is that both aerials should see the same RF field
to work. If one aerial is much closer to the ground or buildings it can cancel
any advantage as Rx signal power can actually be lost in the lower aerial!

   ÃÅÅÅÅÅ  - - - - - - - -  Even Dx
   ³           _   - - - -  RF Field
   ÃÅÅÅÅÅ -   / \    - - -
   ³         ³   ³
ÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄ

SIDE LOBES
The baying distance also affects side lobe nulls. This is very difficult to get
right, as a fraction of a wavelength of boom location or movement can cause
tightly nulled out lobes to reappear.

    Single Aerial                    Bayed @ an exact multiple of « wavelenths

 .       ___       Side                                 Nulled Side
/|\     /   `\.   Lobes                       .ÄÄ....__   Lobes
Beam   | Main  `\v^v/³_     Aerial         ,/'  Main   ``-...__   ÃÄÅÄÅÄÅÄÅÅ´
Width ³  Front    @   _) ÃÄÅÄÅÄÅÄÅÅ´       ³   Front       @ __)    Aerials
 |     | Lobe  ./^v^\³ Back                `\  Lobe  __..-'''Back ÃÄÅÄÅÄÅÄÅÅ´
\|/     \___./'        Lobe                  ``ÄÄ''''        Lobe
 '      --Gain----                          -----Gain------ 



See my bulletins on 4x Power Splitters for 2M & 70cm, Making a Phasing Harness.


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