Playing with HDTV Antennas
With the CBCinstalling an HDTV transmitter in the area, I decided to look at OTA (off-the-air) HDTV as an alternative to Starchoice HDTV. With the transmitter site no more than 25 kms from my house, rabbit ears or a folded dipole probably would work ok, but I’m hoping some of the other networks will also implement HDTV in the Ottawa Valley, so I thought I would put a bit more work into the antenna.
I looked at a number of antenna designs, courtesy of KQ6QV. In the end, I decided to build a Log-Periodic Dipole Array, mostly because it didn’t need a balun. As well, the beamwidth of the LPDA should be wide enough to receive signals from both the Camp Fortune and Manotick transmitter sites.
I modelled 6, 7 and 8 element designs using 4NEC2 with the 8 element design having the fewest anomolies in the design range, when taking into account the need to use a relatively low impedance boom/transmission line. With the 6 and 7 element designs I modelled, the larger dipoles in the array affected both the impedance and front-to-back ratio when these elements became full-wave dipoles at certain frequencies.
Element # |
Element Length (mm) |
Cumulative Spacing (mm) |
1 |
316 |
0 |
2 |
282 |
55 |
3 |
252 |
104 |
4 |
226 |
147 |
5 |
202 |
186 |
6 |
180 |
221 |
7 |
160 |
252 |
8 |
144 |
280 |
I used hobby store 7/32 inch square brass tubing 30 cms in length for the two boom sections and bits of lexan to separate them by approx 5.5 mm to achieve a boom impedance of approximately 125 ohms. The coax is stripped of it’s outer insulator and ran through one of the booms to form an ‘infinite balun’ in an effort to keep stray currents off the outside of the shield, which could upset the balance of the antenna.
It seems to work well, but the signal from the CBC transmitter is so strong I can receive it by pointing the antenna at my neighbour’s house to receive the reflection, so I’ll have to do some testing to see if it performs as modelled by NEC 2.
Here is the NEC file for the antenna. I recommend Arie’s
4NEC2CM 8 ELEMENT LPDA
CM 470-810 MHz
CE
GW 1 21 0 -0.158 0 0 0.158 0 0.00081
GW 2 21 0.055 -0.141 0 0.055 0.141 0 0.00081
GW 3 19 0.104 -0.126 0 0.104 0.126 0 0.00081
GW 4 17 0.147 -0.113 0 0.147 0.113 0 0.00081
GW 5 17 0.186 -0.101 0 0.186 0.101 0 0.00081
GW 6 15 0.221 -0.090 0 0.221 0.090 0 0.00081
GW 7 15 0.252 -0.080 0 0.252 0.080 0 0.00081
GW 8 13 0.280 -0.072 0 0.280 0.072 0 0.00081
GE 0 0 0.
EX 0 8 7 00 1. 0.
FR 0, 96, 0,0, 470, 5
PT -1
TL 1 11 2 11 -125 0. 0. 0. 0. 0.
TL 2 11 3 10 -125 0. 0. 0. 0. 0.
TL 3 10 4 9 -125 0. 0. 0. 0. 0.
TL 4 9 5 9 -125 0. 0. 0. 0. 0.
TL 5 9 6 8 -125 0. 0. 0. 0. 0.
TL 6 8 7 8 -125 0. 0. 0. 0. 0.
TL 7 8 8 7 -125 0. 0. 0. 0. 0.
RP 0 1 10 1510 90. 0. 0. 20. 0. 0.
EN
As well, I was asked for the dimensions for a bowtie antenna. I converted the DB2a from KQ6QV’s website to a standard NEC 2 input card. In essence, the reflector can be any metallic structure, including a wire mesh, as long as the rectangles are less than 1/10 lambda at the highest operating frequency. Each element of the bowtie is approximately 16 cms long and the transmission line between the two bowties is 18.8 cm long with 4.4 cm spacing, using 4mm diameter wire.
CM DB2 bowtie antenna KQ6QV
CM using short segments in reflector to respect the 1500 segment limit
CE
GW 1 1 .0 -.225 .175 .0 -.1125 .175 .003076
GW 2 1 .0 -.1125 .175 .0 .0 .175 .003076
GW 3 1 .0 .0 .175 .0 .1125 .175 .003076
GW 4 1 .0 .1125 .175 .0 .225 .175 .003076
GW 5 1 .0 -.225 .151667 .0 -.1125 .151667 .003076
GW 6 1 .0 -.1125 .151667 .0 .0 .151667 .003076
GW 7 1 .0 .0 .151667 .0 .1125 .151667 .003076
GW 8 1 .0 .1125 .151667 .0 .225 .151667 .003076
GW 9 1 .0 -.225 .128333 .0 -.1125 .128333 .003076
GW 10 1 .0 -.1125 .128333 .0 .0 .128333 .003076
GW 11 1 .0 .0 .128333 .0 .1125 .128333 .003076
GW 12 1 .0 .1125 .128333 .0 .225 .128333 .003076
GW 13 1 .0 -.225 .105 .0 -.1125 .105 .003076
GW 14 1 .0 -.1125 .105 .0 .0 .105 .003076
GW 15 1 .0 .0 .105 .0 .1125 .105 .003076
GW 16 1 .0 .1125 .105 .0 .225 .105 .003076
GW 17 1 .0 -.225 .081667 .0 -.1125 .081667 .003076
GW 18 1 .0 -.1125 .081667 .0 .0 .081667 .003076
GW 19 1 .0 .0 .081667 .0 .1125 .081667 .003076
GW 20 1 .0 .1125 .081667 .0 .225 .081667 .003076
GW 21 1 .0 -.225 .058333 .0 -.1125 .058333 .003076
GW 22 1 .0 -.1125 .058333 .0 .0 .058333 .003076
GW 23 1 .0 .0 .058333 .0 .1125 .058333 .003076
GW 24 1 .0 .1125 .058333 .0 .225 .058333 .003076
GW 25 1 .0 -.225 .035 .0 -.1125 .035 .003076
GW 26 1 .0 -.1125 .035 .0 .0 .035 .003076
GW 27 1 .0 .0 .035 .0 .1125 .035 .003076
GW 28 1 .0 .1125 .035 .0 .225 .035 .003076
GW 29 1 .0 -.225 .011667 .0 -.1125 .011667 .003076
GW 30 1 .0 -.1125 .011667 .0 .0 .011667 .003076
GW 31 1 .0 .0 .011667 .0 .1125 .011667 .003076
GW 32 1 .0 .1125 .011667 .0 .225 .011667 .003076
GW 33 1 .0 -.225 -.011667 .0 -.1125 -.011667 .003076
GW 34 1 .0 -.1125 -.011667 .0 .0 -.011667 .003076
GW 35 1 .0 .0 -.011667 .0 .1125 -.011667 .003076
GW 36 1 .0 .1125 -.011667 .0 .225 -.011667 .003076
GW 37 1 .0 -.225 -.035 .0 -.1125 -.035 .003076
GW 38 1 .0 -.1125 -.035 .0 .0 -.035 .003076
GW 39 1 .0 .0 -.035 .0 .1125 -.035 .003076
GW 40 1 .0 .1125 -.035 .0 .225 -.035 .003076
GW 41 1 .0 -.225 -.058333 .0 -.1125 -.058333 .003076
GW 42 1 .0 -.1125 -.058333 .0 .0 -.058333 .003076
GW 43 1 .0 .0 -.058333 .0 .1125 -.058333 .003076
GW 44 1 .0 .1125 -.058333 .0 .225 -.058333 .003076
GW 45 1 .0 -.225 -.081667 .0 -.1125 -.081667 .003076
GW 46 1 .0 -.1125 -.081667 .0 .0 -.081667 .003076
GW 47 1 .0 .0 -.081667 .0 .1125 -.081667 .003076
GW 48 1 .0 .1125 -.081667 .0 .225 -.081667 .003076
GW 49 1 .0 -.225 -.105 .0 -.1125 -.105 .003076
GW 50 1 .0 -.1125 -.105 .0 .0 -.105 .003076
GW 51 1 .0 .0 -.105 .0 .1125 -.105 .003076
GW 52 1 .0 .1125 -.105 .0 .225 -.105 .003076
GW 53 1 .0 -.225 -.128333 .0 -.1125 -.128333 .003076
GW 54 1 .0 -.1125 -.128333 .0 .0 -.128333 .003076
GW 55 1 .0 .0 -.128333 .0 .1125 -.128333 .003076
GW 56 1 .0 .1125 -.128333 .0 .225 -.128333 .003076
GW 57 1 .0 -.225 -.151667 .0 -.1125 -.151667 .003076
GW 58 1 .0 -.1125 -.151667 .0 .0 -.151667 .003076
GW 59 1 .0 .0 -.151667 .0 .1125 -.151667 .003076
GW 60 1 .0 .1125 -.151667 .0 .225 -.151667 .003076
GW 61 1 .0 -.225 -.175 .0 -.1125 -.175 .003076
GW 62 1 .0 -.1125 -.175 .0 .0 -.175 .003076
GW 63 1 .0 .0 -.175 .0 .1125 -.175 .003076
GW 64 1 .0 .1125 -.175 .0 .225 -.175 .003076
GW 65 1 .0 -.225 .175 .0 -.225 .151667 .003076
GW 66 1 .0 -.225 .151667 .0 -.225 .128333 .003076
GW 67 1 .0 -.225 .128333 .0 -.225 .105 .003076
GW 68 1 .0 -.225 .105 .0 -.225 .081667 .003076
GW 69 1 .0 -.225 .081667 .0 -.225 .058333 .003076
GW 70 1 .0 -.225 .058333 .0 -.225 .035 .003076
GW 71 1 .0 -.225 .035 .0 -.225 .011667 .003076
GW 72 1 .0 -.225 .011667 .0 -.225 -.011667 .003076
GW 73 1 .0 -.225 -.011667 .0 -.225 -.035 .003076
GW 74 1 .0 -.225 -.035 .0 -.225 -.058333 .003076
GW 75 1 .0 -.225 -.058333 .0 -.225 -.081667 .003076
GW 76 1 .0 -.225 -.081667 .0 -.225 -.105 .003076
GW 77 1 .0 -.225 -.105 .0 -.225 -.128333 .003076
GW 78 1 .0 -.225 -.128333 .0 -.225 -.151667 .003076
GW 79 1 .0 -.225 -.151667 .0 -.225 -.175 .003076
GW 80 1 .0 -.1125 .175 .0 -.1125 .151667 .003076
GW 81 1 .0 -.1125 .151667 .0 -.1125 .128333 .003076
GW 82 1 .0 -.1125 .128333 .0 -.1125 .105 .003076
GW 83 1 .0 -.1125 .105 .0 -.1125 .081667 .003076
GW 84 1 .0 -.1125 .081667 .0 -.1125 .058333 .003076
GW 85 1 .0 -.1125 .058333 .0 -.1125 .035 .003076
GW 86 1 .0 -.1125 .035 .0 -.1125 .011667 .003076
GW 87 1 .0 -.1125 .011667 .0 -.1125 -.011667 .003076
GW 88 1 .0 -.1125 -.011667 .0 -.1125 -.035 .003076
GW 89 1 .0 -.1125 -.035 .0 -.1125 -.058333 .003076
GW 90 1 .0 -.1125 -.058333 .0 -.1125 -.081667 .003076
GW 91 1 .0 -.1125 -.081667 .0 -.1125 -.105 .003076
GW 92 1 .0 -.1125 -.105 .0 -.1125 -.128333 .003076
GW 93 1 .0 -.1125 -.128333 .0 -.1125 -.151667 .003076
GW 94 1 .0 -.1125 -.151667 .0 -.1125 -.175 .003076
GW 95 1 .0 .0 .175 .0 .0 .151667 .003076
GW 96 1 .0 .0 .151667 .0 .0 .128333 .003076
GW 97 1 .0 .0 .128333 .0 .0 .105 .003076
GW 98 1 .0 .0 .105 .0 .0 .081667 .003076
GW 99 1 .0 .0 .081667 .0 .0 .058333 .003076
GW 100 1 .0 .0 .058333 .0 .0 .035 .003076
GW 101 1 .0 .0 .035 .0 .0 .011667 .003076
GW 102 1 .0 .0 .011667 .0 .0 -.011667 .003076
GW 103 1 .0 .0 -.011667 .0 .0 -.035 .003076
GW 104 1 .0 .0 -.035 .0 .0 -.058333 .003076
GW 105 1 .0 .0 -.058333 .0 .0 -.081667 .003076
GW 106 1 .0 .0 -.081667 .0 .0 -.105 .003076
GW 107 1 .0 .0 -.105 .0 .0 -.128333 .003076
GW 108 1 .0 .0 -.128333 .0 .0 -.151667 .003076
GW 109 1 .0 .0 -.151667 .0 .0 -.175 .003076
GW 110 1 .0 .1125 .175 .0 .1125 .151667 .003076
GW 111 1 .0 .1125 .151667 .0 .1125 .128333 .003076
GW 112 1 .0 .1125 .128333 .0 .1125 .105 .003076
GW 113 1 .0 .1125 .105 .0 .1125 .081667 .003076
GW 114 1 .0 .1125 .081667 .0 .1125 .058333 .003076
GW 115 1 .0 .1125 .058333 .0 .1125 .035 .003076
GW 116 1 .0 .1125 .035 .0 .1125 .011667 .003076
GW 117 1 .0 .1125 .011667 .0 .1125 -.011667 .003076
GW 118 1 .0 .1125 -.011667 .0 .1125 -.035 .003076
GW 119 1 .0 .1125 -.035 .0 .1125 -.058333 .003076
GW 120 1 .0 .1125 -.058333 .0 .1125 -.081667 .003076
GW 121 1 .0 .1125 -.081667 .0 .1125 -.105 .003076
GW 122 1 .0 .1125 -.105 .0 .1125 -.128333 .003076
GW 123 1 .0 .1125 -.128333 .0 .1125 -.151667 .003076
GW 124 1 .0 .1125 -.151667 .0 .1125 -.175 .003076
GW 125 1 .0 .225 .175 .0 .225 .151667 .003076
GW 126 1 .0 .225 .151667 .0 .225 .128333 .003076
GW 127 1 .0 .225 .128333 .0 .225 .105 .003076
GW 128 1 .0 .225 .105 .0 .225 .081667 .003076
GW 129 1 .0 .225 .081667 .0 .225 .058333 .003076
GW 130 1 .0 .225 .058333 .0 .225 .035 .003076
GW 131 1 .0 .225 .035 .0 .225 .011667 .003076
GW 132 1 .0 .225 .011667 .0 .225 -.011667 .003076
GW 133 1 .0 .225 -.011667 .0 .225 -.035 .003076
GW 134 1 .0 .225 -.035 .0 .225 -.058333 .003076
GW 135 1 .0 .225 -.058333 .0 .225 -.081667 .003076
GW 136 1 .0 .225 -.081667 .0 .225 -.105 .003076
GW 137 1 .0 .225 -.105 .0 .225 -.128333 .003076
GW 138 1 .0 .225 -.128333 .0 .225 -.151667 .003076
GW 139 1 .0 .225 -.151667 .0 .225 -.175 .003076
GW 140 5 0.102 0.022 0.000 0.102 -0.022 0.000 .002
GW 141 6 0.102 0.022 0.000 0.102 0.022 0.094 .002
GW 142 1 0.102 0.022 0.094 0.102 0.022 0.107 .002
GW 143 10 0.102 0.022 0.094 0.127 0.173 0.048 .002
GW 144 10 0.102 0.022 0.107 0.127 0.173 0.150 .002
GW 145 6 0.102 -0.022 0.000 0.102 -0.022 0.094 .002
GW 146 1 0.102 -0.022 0.094 0.102 -0.022 0.107 .002
GW 147 10 0.102 -0.022 0.094 0.127 -0.173 0.048 .002
GW 149 10 0.102 -0.022 0.107 0.127 -0.173 0.150 .002
GW 149 6 0.102 0.022 0.000 0.102 0.022 -0.094 .002
GW 150 1 0.102 0.022 -0.094 0.102 0.022 -0.107 .002
GW 151 10 0.102 0.022 -0.094 0.127 0.173 -0.048 .002
GW 152 10 0.102 0.022 -0.107 0.127 0.173 -0.150 .002
GW 153 6 0.102 -0.022 0.000 0.102 -0.022 -0.094 .002
GW 154 1 0.102 -0.022 -0.094 0.102 -0.022 -0.107 .002
GW 155 10 0.102 -0.022 -0.094 0.127 -0.173 -0.048 .002
GW 156 10 0.102 -0.022 -0.107 0.127 -0.173 -0.150 .002
GE 0 0 0.
EX 0 140 3 00 1. 0.
FR 0, 43, 0,0, 470, 10
PT -1
RP 0 1 10 1510 90. 0. 0. 20. 0. 0.
EN