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, wideband FM Yagi to the TV band and then reoptimized it. The resulting antenna has a boom length of 32″, longest element of 33″, and direct 75Ω feed. Forward gain ranges from 5.3 to 7.2 dBd and the worst backlobe is more than 21 dB down across the entire band. The clean pattern can suppress multipath and co-channel interference.
I designed the antenna using the global optimizer and response flattener of the AO 8.06 Antenna Optimizer program. 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.
Below are calculated performance figures at the channel centers for a segmentation density of 28 segments per halfwave. Mismatch loss is due to SWR. Wire loss is due to conductor resistance. Mismatched gain is forward gain including wire and mismatch losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane. The SWR reference impedance is 75Ω.
177.000 MHz: Impedance 70.0 - j9.4 ohms
SWR 1.16
Mismatch Loss 0.02 dB
Wire Loss 0.01 dB
Mismatched Gain 5.34 dBd
F/R 22.89 dB
183.000 MHz: Impedance 86.4 - j8.8 ohms
SWR 1.20
Mismatch Loss 0.03 dB
Wire Loss 0.01 dB
Mismatched Gain 5.36 dBd
F/R 22.00 dB
189.000 MHz: Impedance 92.0 - j9.9 ohms
SWR 1.27
Mismatch Loss 0.06 dB
Wire Loss 0.01 dB
Mismatched Gain 5.53 dBd
F/R 21.51 dB
195.000 MHz: Impedance 89.2 - j8.0 ohms
SWR 1.22
Mismatch Loss 0.04 dB
Wire Loss 0.01 dB
Mismatched Gain 5.90 dBd
F/R 21.53 dB
201.000 MHz: Impedance 79.9 + j0.0 ohms
SWR 1.07
Mismatch Loss 0.00 dB
Wire Loss 0.01 dB
Mismatched Gain 6.40 dBd
F/R 21.78 dB
207.000 MHz: Impedance 69.9 + j16.9 ohms
SWR 1.28
Mismatch Loss 0.06 dB
Wire Loss 0.01 dB
Mismatched Gain 6.85 dBd
F/R 21.92 dB
213.000 MHz: Impedance 74.3 + j33.8 ohms
SWR 1.57
Mismatch Loss 0.22 dB
Wire Loss 0.02 dB
Mismatched Gain 7.07 dBd
F/R 21.79 dB
174-216 MHz Yagi
Free Space Symmetric
174 177 180 186 192 198 204 210 214 216 MHz
5 6063-T832 wires, inches
ang = 17.49393
r = 16.21429
de = 14.82698
d1 = 12.89202
d2 = 12.37392
d3 = 11.14296
dep = 8.704022
d1p = 11.54469
d2p = 17.901
d3p = 31.44403
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
28 segments/halfwave best matches NEC
Trade-offs: 30% gain, 70% F/B
Frequency weighting: average for gain, worst-case for F/B
Enable bent-wire correction
Channel 7 174-180 MHz
8 180-186
9 186-192
10 192-198
11 198-204
12 204-210
13 210-216
Use ⅜″ tubing supported by nonconductive mounting brackets. Symbols r, de, d1, d2, and d3 are element half-lengths (center to tip), dep, d1p, d2p, and d3p are element positions (center to center) relative to the reflector position of 0, and ang is the driven-element angle. Split the driven element leaving a gap no larger than ¼″, angle each half 17.5° so that the tips are 4¼″ center-to-center from the reflector, and feed with 75Ω coax through a ferrite choke. Keep the stripped coax leads as short as possible.
88–108 MHz