I noticed that the 174–216 MHz VHF-TV band was almost exactly twice the frequency of the 88–108 MHz FM broadcast band. Since the relative bandwidths were nearly equal, I scaled a small FM Yagi to the TV band and then reoptimized it. The resulting antenna has a 32″ boom, 32½″ longest element, and direct 75Ω feed. Forward gain is 5.3–7.2 dBd and the worst backlobe is 21–23 dB down across the band. The clean pattern can suppress multipath and co-channel interference.
I designed the antenna using the AO 9.50 Antenna Optimizer. This image shows the antenna geometry. The red dot is the feedpoint. The bent driven element increases F/B at the low end of the band and the gain everywhere.
Calculated performance is for 28 analysis segments per halfwave. Forward gain includes mismatch and conductor losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane.
Channel Frequency Impedance SWR Mismatch Conductor Forward F/R
MHz ohms Loss dB Loss dB Gain dBd dB
7 177 67.9 - j3.7 1.12 0.01 0.01 5.34 23.31
8 183 87.4 - j3.6 1.17 0.03 0.01 5.35 22.47
9 189 94.4 - j6.9 1.28 0.06 0.01 5.51 21.36
10 195 91.5 - j7.0 1.24 0.05 0.01 5.87 21.44
11 201 81.6 + j0.1 1.09 0.01 0.01 6.39 22.26
12 207 72.1 + j16.1 1.25 0.05 0.01 6.85 22.59
13 213 75.9 + j26.5 1.42 0.13 0.03 7.14 22.01
174-216 MHz Yagi Free Space Symmetric 174 177 180 186 192 198 204 210 214 216 MHz 5 6063-T832 wires, inches ang = 16.25619 r = 16.19217 de = 14.82229 d1 = 12.91589 d2 = 12.36376 d3 = 11.0753 dep = 7.896689 d1p = 10.70153 d2p = 17.40806 d3p = 31.29251 1 0 0 0 0 r 0 .375 1 d1p 0 0 d1p d1 0 .375 1 d2p 0 0 d2p d2 0 .375 1 d3p 0 0 d3p d3 0 .375 shift x dep rotate z -ang 1 0 0 0 0 de 0 .375 1 source Wire 5, end1
Use ⅜″ aluminum tubing mounted through a nonconducing boom or supported by insulated mounting brackets. Symbols r, de, d1, d2, and d3 are element half-lengths (center to tip), dep, d1p, d2p, and d3p are element positions relative to the reflector (center to center), and ang is the driven-element angle. Split the driven element leaving a gap no larger than ¼″ and angle each half 16¼° so that the center of the tips is 3¾″ from the centerline of the reflector. Feed directly with 75Ω coax and use at least one ferrite choke at the feedpoint. Keep the stripped coax leads as short as possible.
The following table shows the degradation of average performance over the channel centers in dB when changing a single dimension by ±⅛″ (±1⁄16″ for symbols that represent element half-length and 2° for ang).
Symbol Gain F/R
ang 0.01 0.47
r 0.02 0.12
de 0.01 0.00
d1 0.02 0.07
d2 0.03 0.20
d3 0.02 0.08
dep 0.01 0.15
d1p 0.01 0.18
d2p 0.01 0.13
d3p 0.00 0.06
I scaled another FM Yagi to the 174–216 MHz TV band. It uses a horizontal folded dipole, three reflectors, and nine elements total. Suppression of co-channel signals matters less for digital TV than for analog FM so I biased the trade-offs toward forward gain and reoptimized the design. The boom lengthened to 82″. Gain is 7.6–10.2 dBd and F/R > 20 dB over the band. A halfwave coaxial balun will match the 300Ω feedpoint to 75Ω coax with negligible loss. Calculated performance is for 28 analysis segments per halfwave. Forward gain includes mismatch and conductor losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane.
Channel Frequency Impedance SWR Mismatch Conductor Forward F/R
MHz ohms Loss dB Loss dB Gain dBd dB
7 177 305 + j34 1.12 0.01 0.01 7.73 22.68
8 183 348 + j5 1.16 0.02 0.01 7.97 21.22
9 189 351 - j19 1.18 0.03 0.01 8.29 20.97
10 195 337 - j20 1.14 0.02 0.01 8.76 21.71
11 201 320 - j9 1.07 0.01 0.01 9.39 20.58
12 207 278 + j19 1.11 0.01 0.01 10.03 22.12
13 213 262 + j112 1.52 0.19 0.03 10.13 23.17
Antenna file:
9-Element VHF-TV Yagi Free Space Symmetric 174 180 186 192 198 204 210 213 216 MHz 11 6063-T832 wires, inches z = 19.92559 r0 = 17.29696 r1 = 17.41426 de = 14.5093 d1 = 12.30237 d2 = 12.21016 d3 = 12.01788 d4 = 11.78023 d5 = 11.33282 de1 = 9.342921 de2 = 12.39683 d1p = 18.30395 d2p = 32.08967 d3p = 46.24657 d4p = 65.10853 d5p = 81.64079 1 0 0 z 0 r1 z .375 1 0 0 0 0 r0 0 .375 1 0 0 -z 0 r1 -z .375 1 de1 0 0 de1 de 0 .375 1 de2 0 0 de2 de 0 .375 1 de1 de 0 de2 de 0 .375 1 d1p 0 0 d1p d1 0 .375 1 d2p 0 0 d2p d2 0 .375 1 d3p 0 0 d3p d3 0 .375 1 d4p 0 0 d4p d4 0 .375 1 d5p 0 0 d5p d5 0 .375 1 source Wire 5, end1
Sensitivity analysis:
Symbol Gain F/R
z 0.00 0.10
r0 0.00 0.10
r1 0.01 0.01
de 0.00 0.04
d1 0.01 0.07
d2 0.03 0.18
d3 0.02 0.24
d4 0.01 0.17
d5 0.01 0.02
de1 0.00 0.01
de2 0.01 0.10
d1p 0.00 0.08
d2p 0.01 0.01
d3p 0.01 0.07
d4p 0.00 0.08
d5p 0.00 0.02
88–108 MHz