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VK2ZRG > TECH 22.03.06 09:44l 135 Lines 5573 Bytes #999 (0) @ WW
BID : 2252_VK2ZRG
Read: DJ7AM DL1LCA GUEST OE7FMI
Subj: 14 element yagi for 23 cm
Path: DB0FHN<DB0MRW<OK0PKL<OK0PCC<OM0PBC<OK0PPL<DB0RES<DK0WUE<I0TVL<ED1ZAC<
IZ0AWG<SP7MGD<VE2PKT<VK2DOT<VK2XGJ<VK2IO<VK2WI
Sent: 060322/0503Z @:VK2WI.#SYD.NSW.AUS.OC #:9368 [SYDNEY] FBB7 $:2252_VK2ZRG
From: VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
To : TECH@WW
VK2ZRG/TPK 1.83d Msg #:2252 Date:22-03-06 Time:4:52Z
Had John G8MNY been courteous enough to ask me if it was OK to republish
my original bulletin, then this is the file that I would have given to him.
If you wish to use this bulletin in your club newsletter etc, then please
ask. Permission will be granted...I just like to know how it gets used.
The entire bulletin including this opening portion must be reproduced. It
may NOT be edited in any way. You may NOT republish this bulletin on packet
radio. (You will demonstrate to the world what a complete a***hole you are
if you do.)
Ralph VK2ZRG 21/3/2006.
Dimensions for 23 cm 14 element yagi with a NON conductive boom.
i.e. Timber, fibreglass, perspex, PVC etc.
Frequency range 1240 to 1300 MHz, with VSWR <1.4:1 when matched at 1270 MHz.
Maximum gain occurs at 1300 MHz, around 15.4 dBi.
Drive point resistance around 28 ohms.
H plane stacking distance is 360 mm.
(i.e. For two horizontally polarised yagis stacked one above the other.)
Design element diameter is 3.2 millimetres.
Range 3 to 3.5 mm. Definitely not over 4 mm
Tolerances : Position +/- 0.5 mm, Length +/- 0.1 mm
Elements
Position Length
0.0 117.0 R
45.0 110.6 D.E
65.0 103.2 D1
97.0 98.8 D2
135.0 96.0 D3
183.0 94.6 D4
235.0 93.4 D5
303.0 92.4 D6
389.0 91.2 D7
479.0 89.4 D8
568.0 88.0 D9
662.0 86.0 D10
760.0 84.0 D11
832.0 82.0 D12
Construction suggestions.
Use aluminium alloy or copper for the elements. Brass could be used but will
reduce the gain slightly. Do NOT use stainless steel. Element length is
critical so you should use vernier calipers to measure the element length.
Cut the elements slightly over length, then file the ends for the correct
length.
The boom material MUST be non conductive. If timber, use western red cedar,
Douglas fir (oregon), or similar soft wood, and paint it (but not the elements)
after the yagi is assembled. If plastic, ensure that the plastic is
UV resistant.
Construction is easier if you use a square or rectangular section boom.
Mark the element positions from a single reference point (to avoid cumulative
errors if you mark element spacing). Drill the element holes in a drill press
if possible, so that the elements will be properly aligned. Drill the holes
slightly under sized so that the elements will be a push fit, or use epoxy
resin adhesive to secure them. You will find that spacing of D 11 and D 12
is less than spacing of D10 and D 11. This is NOT a mistake.
Mast size at 23 cm will be a significant portion of a wavelength so the
yagi should be rear mounted on your antenna mast. A rearward boom extension
of 15 cm should be adequate. A metal tube placed over the boom extension will
prevent crushing of the boom. You could use epoxy resin to attach the metal
tube to the boom extension.
Matching to 50 ohms is best done with a folded dipole. Use a 1.0 mm minor
element diameter in conjunction with the 3 or 3.2 mm major diameter. Spacing
should be 9 mm with 3.2 mm, or 7 mm for 3.0 dia (centre to centre). The spacing
isn't critical. Use a 4:1 balun made from small diameter 75 (or 50) ohm teflon
co-axial cable. (The optimum impedance for the balun section is 100 ohms.)
A length of 82 mm should be about right.
Performance data from two yagi analysis programmes.
Increasing element diameter will lower the maximum operating frequency of
this antenna. Increased element diameter will also increase the gain at a
given frequency and reduce the drive impedance. Performance will be quite OK
with 4 mm elements for the full 1240 to 1300 MHz range. If the yagi is to be
used only for 1240 to 1270 MHz, you could use 4.75 mm diameter elements.
Note. F/R is front to rear. This includes all lobes (at any angle) in the rear
180 deg part of the pattern. F/R and F/B ratios are for the E plane.
These data for 3.0 mm dia aluminium elements.
Performance predictions from Brian Beezley's (K6STI) YA.EXE
MHz GAIN dBi F/R dB IMPEDANCE ohms VSWR
1240 14.10 27.0 28.9 -j5.9 1.35
1260 14.58 28.3 29.1 +j0.9 1.10
1270 14.80 26.0 29.2 +j2.8 1.00
1280 15.00 26.1 29.3 +j5.2 1.09
1300 15.31 25.4 28.1 +j8.5 1.23
These data for 3.2 mm dia aluminium elements.
Performance predictions from Brian Beezley's (K6STI) YA.EXE
MHz GAIN dBi F/R dB IMPEDANCE ohms VSWR
1240 14.25 27.0 28.2 -j4.9 1.34
1260 14.71 28.0 28.5 +j0.9 1.10
1270 14.92 26.0 28.7 +j3.5 1.00
1280 15.11 25.9 28.7 +j5.7 1.08
1300 15.38 25.4 27.0 +j8.3 1.20
1310 15.44 25.7 24.0 +j9.1 1.33
1320 15.46 25.9 18.2 +j11.2 1.76
Performance predictions from Lew Gordon's (K4VX) YAGIMAX 3.11
MHz GAIN dBi F/B dB IMPEDANCE ohms VSWR E/H BEAM 1st E/H Side lobes
1240 14.08 23.68 31.23-j5.17 1.37 38/42 deg -20/-16 dB
1260 14.60 27.00 30.26+j0.89 1.13
1270 14.86 30.55 29.65+j4.51 1.00 36/40 deg -22/-18 dB
1280 15.10 31.96 29.51+j8.33 1.14
1300 15.51 23.59 30.78+j12.69 1.32 34/36 deg -25/-22 dB
1310 15.67 21.51 28.35+j11.29 1.27
1320 15.81 21.03 20.10+j12.07 1.65
The E and H plane side lobe levels and beam widths were "eyeballed" from the
computer screen.
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
Taglines by Colin Coker G4FCN
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