The Finco FM-4 is dual-drive Yagi with six elements on a 92″ boom. It was once manufactured by the Finney Company. The design dates from the early 1960s. Model FM-4G added gold-colored “corrodizing.”
I modeled the antenna with the AO 9.67 Antenna Optimizer program. This image shows the antenna geometry. The shorting straps on the driven elements broadband the response.
This image shows the segmentation of the driven elements and phasing line. Blue dots mark analysis segments. The red dot is the feedpoint.
I found this FM-4 at a garage sale in the early 1970s. I still use it today. An instruction sheet is here.
Calculated performance is for 28 analysis segments per conductor 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.
Frequency Impedance SWR Mismatch Conductor Forward F/R
MHz ohms Loss dB Loss dB Gain dBd dB
88 220+j77 1.54 0.20 0.01 6.26 16.57
89 222+j90 1.58 0.22 0.01 6.22 17.69
90 226+j94 1.58 0.23 0.01 6.22 18.56
91 227+j94 1.57 0.22 0.01 6.25 19.31
92 227+j90 1.56 0.21 0.01 6.30 20.09
93 223+j84 1.55 0.21 0.01 6.37 20.56
94 217+j78 1.56 0.21 0.01 6.45 20.86
95 207+j71 1.59 0.23 0.01 6.52 21.13
96 194+j68 1.68 0.29 0.01 6.58 21.34
97 181+j67 1.78 0.36 0.01 6.62 21.61
98 165+j65 1.94 0.47 0.01 6.64 21.98
99 153+j70 2.10 0.59 0.02 6.64 22.18
100 143+j77 2.28 0.72 0.02 6.64 22.39
101 134+j86 2.46 0.85 0.02 6.63 22.59
102 129+j96 2.61 0.96 0.02 6.64 22.52
103 127+j106 2.71 1.04 0.02 6.68 20.82
104 129+j116 2.74 1.06 0.02 6.76 19.44
105 136+j122 2.65 0.99 0.02 6.92 18.32
106 150+j123 2.42 0.82 0.03 7.13 17.56
107 164+j110 2.16 0.63 0.03 7.33 16.97
108 168+j77 1.95 0.48 0.04 7.41 16.61
Finco FM-4 Free Space 98 MHz 49 6063-T832 wires, inches rp = 0 de1p = 20.5 de2p = 37.5 d1p = 49.5 d2p = 70.5 d3p = 91.5 r = 34 de1 = 30 de2 = 23 d1 = 25.5 d2 = 25.5 d3 = 23.5 de1s = 10 de2s = 12 d = .375 ; Tubing diameter eqd = 1.35 ; Equivalent diameter of 0.5" sheath at bracket b = 2.3125 ; Bracket half-length w = .11 ; Phasing line diameter x1 = 31.5 xm = 33.5 x2 = 35.5 f = 25 ; Another boom hole at 28.25 1 rp -r 0 rp -b 0 d ; Reflector 1 rp -b 0 rp b 0 eqd 1 rp b 0 rp r 0 d 1 de1p -de1 -2 de1p -de1s -2 .375 ; Driven element 1 1 de1p -de1s -2 de1p -1 -2 .375 1 de1p 1 -2 de1p de1s -2 .375 1 de1p de1s -2 de1p de1 -2 .375 1 de1p -de1 0 de1p -de1s 0 .375 1 de1p -de1s 0 de1p -b 0 .375 1 de1p -b 0 de1p b 0 eqd 1 de1p b 0 de1p de1s 0 .375 1 de1p de1s 0 de1p de1 0 .375 1 de1p -de1 -2 de1p -de1 0 .375 1 de1p de1 -2 de1p de1 0 .375 1 de1p -de1s -2 de1p -de1s 0 .375 1 de1p de1s -2 de1p de1s 0 .375 1 de2p -de2 -2 de2p -de2s -2 .375 ; Driven element 2 1 de2p -de2s -2 de2p -1 -2 .375 1 de2p 1 -2 de2p de2s -2 .375 1 de2p de2s -2 de2p de2 -2 .375 1 de2p -de2 0 de2p -de2s 0 .375 1 de2p -de2s 0 de2p -b 0 .375 1 de2p -b 0 de2p b 0 eqd 1 de2p b 0 de2p de2s 0 .375 1 de2p de2s 0 de2p de2 0 .375 1 de2p -de2 -2 de2p -de2 0 .375 1 de2p de2 -2 de2p de2 0 .375 1 de2p -de2s -2 de2p -de2s 0 .375 1 de2p de2s -2 de2p de2s 0 .375 1 d1p -d1 0 d1p -b 0 d ; Directors 1 d1p -b 0 d1p b 0 eqd 1 d1p b 0 d1p d1 0 d 1 d2p -d2 0 d2p -b 0 d 1 d2p -b 0 d2p b 0 eqd 1 d2p b 0 d2p d2 0 d 1 d3p -d3 0 d3p -b 0 d 1 d3p -b 0 d3p b 0 eqd 1 d3p b 0 d3p d3 0 d 1 de1p -1 -2 f -1 -2 w ; Phasing line 1 f -1 -2 x1 -1 -2 w 1 x1 -1 -2 xm 0 -1.125 w 1 xm 0 -1.125 x2 1 -2 w 1 x2 1 -2 de2p 1 -2 w 1 de1p 1 -2 f 1 -2 w 1 f 1 -2 x1 1 -2 w 1 x1 1 -2 xm 0 -2.875 w 1 xm 0 -2.875 x2 -1 -2 w 1 x2 -1 -2 de2p -1 -2 w 1 f 1 -2 f -1 -2 w 1 source Wire 49, center This models the Finco FM-4 receiving antenna for the FM broadcast band. The elements use a 0.5"-diameter reinforcing sheath that I included in the mounting bracket model. It extends about 1.5" past the bracket, which I ignored. The FM-4 has two possible mounting holes in the boom for the feed bracket. I developed this model to determine where to place the bracket on a used FM-4 that lacked assembly instructions.
88–108 MHz