| |
G8MNY > TECH 18.01.11 10:32l 102 Lines 4513 Bytes #999 (0) @ WW
BID : 5053_GB7CIP
Read: GUEST OE7FMI
Subj: Stacking, Baying or Boxing Ant
Path: DB0FHN<DB0FOR<DB0SIF<DB0MRW<DK0WUE<IK6ZDE<VE3UIL<ZS0MEE<UA6ADV<GB7CIP
Sent: 110117/2345Z @:GB7CIP.#32.GBR.EU #:5053 [Caterham] $:5053_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
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 opertunity if Dx stations are not aroung 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.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
