After Antennacraft, Channel Master, Finco, and Winegard stopped selling outdoor directional FM antennas, I decided to design an antenna anyone could build from parts available locally. This Yagi uses items from Home Depot. It has two reflectors, a loop-coupled driven element, and seven directors, all made of ½″ copper pipe, on a 122″ boom made of 1½″ ABS pipe. The red dot marks the 75Ω feedpoint. I optimized the design with the AO 9.67 Antenna Optimizer.
The loop couples to the first director in a way that greatly improves the pattern. It yields higher forward gain than a horizontal folded dipole and does not require a 300Ω balun. It does need a series capacitor at the feedpoint. This is the only part not available at Home Depot.
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 76.7+j8.8 1.13 0.02 0.01 7.27 30.48
89 73.3-j2.7 1.04 0.00 0.01 7.36 31.13
90 67.6-j6.6 1.15 0.02 0.01 7.44 31.24
91 63.3-j6.0 1.21 0.04 0.01 7.54 31.36
92 60.9-j3.2 1.24 0.05 0.01 7.67 31.50
93 60.6+j0.6 1.24 0.05 0.01 7.81 30.68
94 62.3+j4.8 1.22 0.04 0.01 7.96 30.31
95 65.4+j8.5 1.20 0.04 0.01 8.12 30.38
96 69.9+j11.0 1.18 0.03 0.01 8.28 30.74
97 75.7+j12.1 1.17 0.03 0.01 8.44 31.17
98 81.9+j11.0 1.18 0.03 0.01 8.60 31.09
99 87.3+j7.6 1.20 0.03 0.01 8.75 30.80
100 90.8+j2.5 1.21 0.04 0.01 8.89 30.60
101 92.6-j3.1 1.24 0.05 0.01 9.01 30.63
102 93.9-j8.6 1.28 0.07 0.01 9.09 30.91
103 94.2-j14.4 1.33 0.09 0.02 9.14 30.88
104 92.5-j22.1 1.40 0.12 0.02 9.12 30.01
105 85.8-j31.1 1.50 0.18 0.02 9.00 30.58
106 72.4-j32.6 1.55 0.21 0.03 8.82 31.09
107 64.5-j18.9 1.36 0.10 0.03 8.65 30.42
108 93.1+j8.5 1.27 0.06 0.05 8.27 30.13
Use five ten-foot lengths of ½″ Type M (0.028″ wall) or Type L (0.04″ wall) copper pipe (0.625″ OD) to make the elements. The boom is a ten-foot length of 1½″ ABS pipe (1.9″ OD). Use short lengths of ABS pipe and an ABS Tee to support the reflectors. Make the loop from soldered copper pipe scraps. Measure all dimensions to the conductor centerline. The loop must be in the antenna plane in front of the driven element. Connect the 75Ω coax shield to one side of the feedpoint gap. Connect the center conductor through an 11 pF 5% ceramic capacitor to the other side. Make the connections as close as possible to the gap, which should be 2 to 6 mm long. Keep all leads as short as possible. Waterproof everything. Use a current choke at the feedpoint.
Use two PVC conduit straps to mount the boom to a flat plate attached to the mast. (You may find five-packs of conduit clamps in the store bin instead of straps. Either should work fine.) Mount the elements above the boom with the straps. Attach the element with two sheet metal screws. Consider using Loctite on the screw threads since the copper is thin. Drill a hole in each strap and secure it to the boom with another screw.
You may need boom guys to prevent sag. Wire is fine for up-guys. In windy areas add a nonconductive horizontal crossboom to the mast to support two sets of nonconductive guys arrayed 120° from the up-guys. Consider reinforcing the longer elements. A centered 24″ dowel will effectively shorten an element 12″ on each side. Due to the limited strength of thin copper, this antenna may not be suitable for locations with high wind, especially where thick ice may form.
Instead of copper pipe, you can use 6063-T5 aluminum angle. Elements made of this material may be stronger than those made of copper pipe. The 0.5″ × 0.5″ right-angle shape is electrically equivalent to a 0.4″ round conductor. After reoptimizing the design for these elements, performance is similar to that of the copper design but with slightly lower forward gain. Use the same boom and conduit straps. For accurate conductor spacing, mount all elements with the angle oriented the same way. Use a 10 pF 5% capacitor.
Check the antenna with a vector network analyzer. Do not alter element lengths or spacings to improve SWR. If you weatherproof it, you can substitute a small air trimmer for the fixed capacitor.
A driven element with lower performance but easier to make is a copper dipole bent at the center with each side angled 5° to the rear. Mount the element halves on a small nonconducting plate attached to the boom with two conduit straps. Attach 75Ω coax with a current choke.
Read these notes before building anything.
The following table shows the largest performance degradation over the antenna file frequencies in dB for the copper loop design when altering a symbol value by Tol.
Performance Comparison
Antenna Files
Home Depot Yagi - Copper Elements
Free Space Symmetric
88 90 92.5 95 98 103 104 106 107 108 MHz
15 copper wires, inches
h = 13.0202 ; reflector height
rp = 0 ; element positions
dep = 11.12226
d1p = 17.6764
d2p = 27.19028
d3p = 44.07455
d4p = 56.26309
d5p = 74.78796
d6p = 94.68615
d7p = 122
r = 35.00171 ; element half-lengths
de = 30.46988
d1 = 25.96496
d2 = 25.42948
d3 = 24.35504
d4 = 24.17117
d5 = 24.47396
d6 = 23.91122
d7 = 21.95754
w = 2.996561 ; loop half-width
s = 4.517059 ; loop side
p = dep + s
1 rp -r h rp r h 0.625
1 rp -r -h rp r -h 0.625
1 dep w 0 dep de 0 0.625
1 dep -w 0 dep -de 0 0.625
6 dep -w 0 dep w 0 0.625
6 p -w 0 p w 0 0.625
4 p w 0 dep w 0 0.625
4 p -w 0 dep -w 0 0.625
1 d1p -d1 0 d1p d1 0 0.625
1 d2p -d2 0 d2p d2 0 0.625
1 d3p -d3 0 d3p d3 0 0.625
1 d4p -d4 0 d4p d4 0 0.625
1 d5p -d5 0 d5p d5 0 0.625
1 d6p -d6 0 d6p d6 0 0.625
1 d7p -d7 0 d7p d7 0 0.625
1 source
Wire 6, center
1 load
c = 11.01768 ; series feedpoint capacitor
Wire 6, center c pF
Home Depot Yagi - Aluminum Angle Elements
Free Space Symmetric
88 90 92.5 95 98 103 104 106 107 108 MHz
15 6063-T832 wires, inches ; actually 6063-T5
h = 13.59818 ; reflector height
rp = 0 ; element positions
dep = 11.24254
d1p = 17.69555
d2p = 24.74784
d3p = 40.55624
d4p = 53.81902
d5p = 72.65115
d6p = 93.68079
d7p = 122
r = 34.89457 ; element half-lengths
de = 31.05756
d1 = 26.43113
d2 = 25.88266
d3 = 24.86955
d4 = 24.57975
d5 = 24.84453
d6 = 24.34787
d7 = 22.13162
w = 2.984501 ; loop half-width
s = 4.410533 ; loop side
p = dep + s
1 rp -r h rp r h 0.4
1 rp -r -h rp r -h 0.4
1 dep w 0 dep de 0 0.4
1 dep -w 0 dep -de 0 0.4
6 dep -w 0 dep w 0 0.4
6 p -w 0 p w 0 0.4
4 p w 0 dep w 0 0.4
4 p -w 0 dep -w 0 0.4
1 d1p -d1 0 d1p d1 0 0.4
1 d2p -d2 0 d2p d2 0 0.4
1 d3p -d3 0 d3p d3 0 0.4
1 d4p -d4 0 d4p d4 0 0.4
1 d5p -d5 0 d5p d5 0 0.4
1 d6p -d6 0 d6p d6 0 0.4
1 d7p -d7 0 d7p d7 0 0.4
1 source
Wire 6, center
1 load
c = 10.34873 ; series feedpoint capacitor
Wire 6, center c pF
Home Depot Yagi - Bent DE
Free Space Symmetric
88 90 92.5 95 98 103 104 106 107 108 MHz
11 copper wires, inches
ang = 4.961757 ; driven element angle
h = 13.87293 ; reflector height
rp = 0 ; element positions
dep = 15.36444
d1p = 19.30658
d2p = 26.15257
d3p = 38.5457
d4p = 52.17861
d5p = 69.66715
d6p = 91.52292
d7p = 122
r = 35.04396 ; element half-lengths
de = 30.82022
d1 = 26.40891
d2 = 25.719
d3 = 24.83018
d4 = 24.60069
d5 = 24.26679
d6 = 23.89873
d7 = 21.65854
1 rp -r h rp r h 0.625
1 rp -r -h rp r -h 0.625
rotate end1 z -ang
1 dep 0 0 dep de 0 0.625
rotate end1 z ang
1 dep 0 0 dep -de 0 0.625
rotate end
1 d1p -d1 0 d1p d1 0 0.625
1 d2p -d2 0 d2p d2 0 0.625
1 d3p -d3 0 d3p d3 0 0.625
1 d4p -d4 0 d4p d4 0 0.625
1 d5p -d5 0 d5p d5 0 0.625
1 d6p -d6 0 d6p d6 0 0.625
1 d7p -d7 0 d7p d7 0 0.625
1 source
Wire 3, end1
Sensitivity Analysis
Symbol Tol Gain F/R
h 0.0394 0.00 0.12
rp 0.0394 0.00 0.11
dep 0.0394 0.01 0.16
d1p 0.0394 0.02 0.12
d2p 0.0394 0.01 0.05
d3p 0.0394 0.00 0.10
d4p 0.0394 0.00 0.14
d5p 0.0394 0.00 0.10
d6p 0.0394 0.00 0.08
d7p 0.0394 0.00 0.09
r 0.0197 0.00 0.28
de 0.0197 0.00 0.06
d1 0.0197 0.02 0.07
d2 0.0197 0.04 0.31
d3 0.0197 0.01 0.24
d4 0.0197 0.02 0.16
d5 0.0197 0.02 0.39
d6 0.0197 0.02 0.42
d7 0.0197 0.01 0.24
w 0.0197 0.01 0.00
s 0.0394 0.02 0.07
c 1.1018 0.23 0.00
December 23, 2022
88–108 MHz