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 √ 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 ______ / \
______ / \ │ │
BAD OVER / \ │ │ │ │ WASTEFUL
LAPPING │ _ _ _ │ │ │ \______/ MAST
│/ \│ \______/ IDEAL SPACING
GAIN │\_ _ _ /│ / \ NO ______ NO
LOSS │ │ │ │ GAIN / \ GAIN
\______/ │ │ LOSS │ │ LOSS
\______/ │ │
\______/

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

Gain
+3dB ─┤ _..... Nearly +3dB
+2dB ─┤ ,/'\._ _./'
+1dB ─┤ ./'\ / "
0dB _│_.,/' `-.-'
─┼───────┬─────────┬─────────┬───── 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 `\ ./' `\. │ ½ │ ./' `\.
│ Beam │ │ ½ Area │ │ Area │ │¼ Area│
\ Area / `\.______./' │ │ `\.__./'
`\.___./' \.__./
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!

├┼┼┼┼┼ - - - - - - - - Even Dx
│ _ - - - - RF Field
├┼┼┼┼┼ - / \ - - -
│ │ │
───┴─────────┴───┴──

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 ½ wavelenths

. ___ Side Nulled Side
/|\ / `\. Lobes .──....__ Lobes
Beam | Main `\v^v/│_ Aerial ,/' Main ``-...__ ├─┼─┼─┼─┼┼┤ Width │ Front @ _) ├─┼─┼─┼─┼┼┤ │ Front @ __) Aerials
| | Lobe ./^v^\│ Back `\ Lobe __..-'''Back ├─┼─┼─┼─┼┼┤ \|/ \___./' Lobe ``──'''' Lobe
' --Gain---- -----Gain------



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


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