Our 16dBi 850MHz Yagi is 1510mm long (including the mounting plate and all elements) This is the length required for an antenna of this gain at this frequency
At 24dBi an 850MHz Yagi would be 15m long ! This is the length required for an antenna of this gain at this centre frequency... but its more complicated than that!
BUYER BEWARE ! Sold as a 22 or 24dBi antenna but is capable of only 14dBi !
These antennas are only 1m in total length. The gain is very much overstated and falsely advertized by several online stores and a number of Telstra Shops.
So far, we have found two "manufacturers" of these identical antennas.
Following our request of both of them to provide Free-Radiation, Gain vs Frequency and VSWR vs freq. test results, to our surprise one of them did actually provide information. The other just ignored us.
The Australian re-sellers we contacted were unwilling to supply any information.
As you can see, the modeling of this antenna produces the same maximum as the manufacturers own test results. That is about 11.5dBi for the telstra 850Mhz band and about 13.5dBi for the Optus 900MHz band.
But the REAL limitation is more to do with bandwidth.
The graph below is show a hypothetical comparison of a very long hi-gain Yagi and a shorter low gain Yagi. The values are purly hypothetical for ilustration purposes only.
All Yagi Antennas have a "Bandwidth" with a maximum gain centered about a particular frequency. As more elements are added to the Yagi it becomes longer and higher in gain at its optimum centre frequency. The Bandwidth however has the opposite reaction and becomes narrower.
From the chart above we can see that as the antenna gets longer, the bandwidth becomes unusable
Gain at operating frequency
Frequency
Long antenna
medium antenna
Short antenna
Receive:
830MHz
16 dBi
15 dbi
13.5 dBi
Transmit:
880Mhz
21 dBi
16.5 dBi
13dBi
Useful bandwidth within 1dB of max gain:
50MHz
90MHz
>100MHz
111
222
333
VK5DJ's YAGI CALCULATOR
Yagi design frequency =860.00 MHz
Wavelength =349 mm
Parasitic elements contacting a square section metal boom 22.00 mm across.
Folded dipole mounted same as directors and reflector
Director/reflector diam =10 mm
Radiator diam =10 mm
REFLECTOR
184 mm long at boom position = 30 mm(IT = 81.0 mm)
RADIATOR
Single dipole 158 mm tip to tip, spaced 70 mm from reflector at boom posn 100 mm (IT = 68.0 mm)
Folded dipole 178 mm tip to tip, spaced 70 mm from reflector at boom posn 100 mm (IT = 78.0 mm)
DIRECTORS
Dir
Length
Spaced
Boom position
IT
Gain
Gain
(no.)
(mm)
(mm)
(mm)
(mm)
(dBd)
(dBi)
1
157
26
126
67.5
4.8
6.9
2
154
63
189
66
6.5
8.6
3
152
75
264
65
7.8
9.9
4
150
87
351
64
8.9
11
5
149
98
448
63.5
9.8
11.9
6
147
105
553
62.5
10.5
12.7
7
145
110
663
61.5
11.2
13.3
8
144
115
778
61
11.7
13.9
9
143
120
898
60.5
12.2
14.4
10
141
125
1023
59.5
12.7
14.9
11
140
131
1154
59
13.1
15.3
12
139
134
1288
58.5
13.5
15.7
13
138
136
1424
58
13.8
16
14
137
138
1562
57.5
14.2
16.3
15
136
139
1702
57
14.5
16.6
16
136
139
1841
57
14.7
16.9
17
135
139
1980
56.5
15
17.1
18
134
139
2120
56
15.2
17.4
19
134
139
2259
56
15.4
17.6
20
133
139
2399
55.5
15.6
17.8
21
132
139
2538
55
15.8
18
22
132
139
2678
55
16
18.2
23
132
139
2817
55
16.2
18.3
24
131
139
2956
54.5
16.4
18.5
25
131
139
3096
54.5
16.5
18.7
26
130
139
3235
54
16.7
18.8
27
130
139
3375
54
16.8
19
28
130
139
3514
54
17
19.1
29
129
139
3654
53.5
17.1
19.2
30
129
139
3793
53.5
17.2
19.4
31
129
139
3933
53.5
17.3
19.5
32
129
139
4072
53.5
17.5
19.6
33
128
139
4211
53
17.6
19.7
34
128
139
4351
53
17.7
19.8
35
128
139
4490
53
17.8
19.9
36
128
139
4630
53
17.9
20
37
128
139
4769
53
18
20.1
38
128
139
4909
53
18.1
20.2
39
127
139
5048
52.5
18.2
20.3
40
127
139
5187
52.5
18.3
20.4
41
127
139
5327
52.5
18.4
20.5
42
127
139
5466
52.5
18.5
20.6
43
127
139
5606
52.5
18.5
20.7
44
127
139
5745
52.5
18.6
20.8
45
127
139
5885
52.5
18.7
20.9
46
127
139
6024
52.5
18.8
20.9
47
127
139
6164
52.5
18.9
21
48
127
139
6303
52.5
18.9
21.1
49
127
139
6442
52.5
19
21.2
50
126
139
6582
52
19.1
21.2
51
126
139
6721
52
19.2
21.3
52
126
139
6861
52
19.2
21.4
53
126
139
7000
52
19.3
21.5
54
126
139
7140
52
19.4
21.5
55
126
139
7279
52
19.4
21.6
56
126
139
7418
52
19.5
21.7
57
126
139
7558
52
19.6
21.7
58
126
139
7697
52
19.6
21.8
59
126
139
7837
52
19.7
21.8
60
126
139
7976
52
19.7
21.9
61
126
139
8116
52
19.8
22
62
126
139
8255
52
19.9
22
63
126
139
8395
52
19.9
22.1
64
126
139
8534
52
20
22.1
65
126
139
8673
52
20
22.2
66
126
139
8813
52
20.1
22.2
67
126
139
8952
52
20.1
22.3
68
126
139
9092
52
20.2
22.3
69
126
139
9231
52
20.2
22.4
70
126
139
9371
52
20.3
22.4
71
126
139
9510
52
20.3
22.5
72
126
139
9649
52
20.4
22.5
73
126
139
9789
52
20.4
22.6
74
126
139
9928
52
20.5
22.6
75
126
139
10068
52
20.5
22.7
76
126
139
10207
52
20.6
22.7
77
126
139
10347
52
20.6
22.8
78
126
139
10486
52
20.7
22.8
79
126
139
10626
52
20.7
22.9
80
126
139
10765
52
20.8
22.9
81
126
139
10904
52
20.8
23
82
126
139
11044
52
20.9
23
83
126
139
11183
52
20.9
23
84
126
139
11323
52
20.9
23.1
85
126
139
11462
52
21
23.1
86
126
139
11602
52
21
23.2
87
126
139
11741
52
21.1
23.2
88
126
139
11880
52
21.1
23.3
89
126
139
12020
52
21.1
23.3
90
126
139
12159
52
21.2
23.3
91
126
139
12299
52
21.2
23.4
92
126
139
12438
52
21.3
23.4
93
126
139
12578
52
21.3
23.4
94
126
139
12717
52
21.3
23.5
95
126
139
12857
52
21.4
23.5
96
126
139
12996
52
21.4
23.6
97
126
139
13135
52
21.4
23.6
98
126
139
13275
52
21.5
23.6
99
126
139
13414
52
21.5
23.7
100
126
139
13554
52
21.6
23.7
101
126
139
13693
52
21.6
23.7
102
126
139
13833
52
21.6
23.8
103
126
139
13972
52
21.7
23.8
104
126
139
14112
52
21.7
23.8
105
126
139
14251
52
21.7
23.9
106
126
139
14390
52
21.8
23.9
107
126
139
14530
52
21.8
23.9
108
126
139
14669
52
21.8
24
COMMENTS
The abbreviation "IT" means "Insert To", it is the construction distance from the element tip to the edge of the boom for through boom mounting
Spacings measured centre to centre from previous element
Tolerance for element lengths is +/- 1 mm
Boom position is the mounting point for each element as measured from the rear of the boom and includes the 30 mm overhang.The total boom length is 14699 mm including two overhangs of 30 mm
The beam's estimated 3dB beamwidth is 13 deg
A half wave 4:1 balun uses 0.66 velocity factor RG-58 (PE)and is 115 mm long plus leads