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 Iím 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 didnít 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 itís outer insulator and ran through one of the booms to form an Ďinfinite baluní 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 neighbourís house to receive the reflection, so Iíll 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 Arieís 4NEC2

CM 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 KQ6QVís 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