Home Depot Yagi

This Yagi uses parts available at Home Depot. It has two reflectors, a loop-coupled driven element, and seven directors, all made of ″ copper pipe, on a 122″ boom made of 1″ ABS pipe. The red dot marks the 75Ω feedpoint. I optimized the design with the AO 9.64 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 75:300Ω balun. It does need a series capacitor at the feedpoint (the only part not available at Home Depot).

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. Forward gain includes mismatch and conductor losses and correction by pattern integration. 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    83.8 + j13.8  1.23     0.05      0.01      7.14      30.00
    89    78.4 - j1.4   1.05     0.00      0.01      7.27      30.44
    90    70.9 - j6.3   1.11     0.01      0.01      7.36      30.48
    91    65.2 - j6.1   1.18     0.03      0.01      7.46      30.58
    92    62.0 - j3.6   1.22     0.04      0.01      7.59      30.72
    93    60.8 - j0.2   1.23     0.05      0.01      7.72      30.62
    94    61.6 + j3.7   1.23     0.05      0.01      7.88      30.14
    95    63.8 + j7.1   1.21     0.04      0.01      8.04      30.08
    96    66.8 + j9.4   1.19     0.03      0.01      8.21      30.46
    97    71.2 + j10.5  1.16     0.03      0.01      8.39      30.66
    98    75.9 + j9.9   1.14     0.02      0.01      8.56      30.64
    99    80.0 + j7.4   1.12     0.01      0.01      8.73      30.43
   100    82.8 + j3.4   1.11     0.01      0.01      8.89      30.35
   101    84.3 - j0.5   1.12     0.01      0.01      9.04      30.51
   102    85.5 - j4.9   1.16     0.02      0.01      9.15      30.83
   103    86.0 - j10.0  1.20     0.04      0.02      9.23      30.86
   104    84.2 - j17.0  1.28     0.06      0.02      9.26      29.91
   105    77.2 - j25.0  1.39     0.12      0.02      9.19      30.47
   106    63.9 - j25.5  1.49     0.17      0.03      9.04      31.04
   107    55.3 - j11.2  1.42     0.13      0.03      8.87      30.40
   108    78.7 + j21.0  1.32     0.08      0.05      8.57      30.01

Ground Effects

I designed the antenna in free space. This shows how ground proximity affects F/R at 1 elevation angle for boom heights between 15 and 50 feet.

Construction

Use five ten-foot lengths of ″ 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 1″ ABS pipe (1.9″ OD). Use a two-foot length of pipe and an ABS Tee to support the reflectors. Make the loop from soldered copper pipe scraps. Measure loop dimensions to the pipe 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 a 12-pF capacitor to the other side. Alternatively, use 24 pF in series with each coax lead. Keep the gap and all leads as short as possible. Waterproof the connections. Use a current balun 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.

Antenna File

Home Depot Yagi
Free Space Symmetric
88 90 92.5 95 98 103 104.5 106 107 108 MHz
15 copper wires, inches
h = 12.533964		; reflector height
rp = 0			; element positions
dep = 10.551616
d1p = 17.108743
d2p = 26.154638
d3p = 42.577044
d4p = 55.602213
d5p = 75.11462
d6p = 94.63302
d7p = 122
r = 34.969866		; element half-lengths
de = 30.529775
d1 = 25.9523
d2 = 25.448524
d3 = 24.21614
d4 = 24.138605
d5 = 24.262525
d6 = 23.92736
d7 = 22.159565
w = 2.9910192		; loop half-width
s = 4.354192		; 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 = 11.645967		; series feedpoint capacitor
Wire 6, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 88, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0394   0.00   0.10
    rp   0.0394   0.00   0.11
   dep   0.0394   0.00   0.15
   d1p   0.0394   0.01   0.11
   d2p   0.0394   0.00   0.07
   d3p   0.0394   0.01   0.12
   d4p   0.0394   0.00   0.11
   d5p   0.0394   0.00   0.12
   d6p   0.0394   0.00   0.13
   d7p   0.0394   0.00   0.11
     r   0.0197   0.00   0.29
    de   0.0197   0.01   0.05
    d1   0.0197   0.02   0.23
    d2   0.0197   0.04   0.59
    d3   0.0197   0.00   0.17
    d4   0.0197   0.02   0.39
    d5   0.0197   0.01   0.37
    d6   0.0197   0.01   0.36
    d7   0.0197   0.00   0.22
     w   0.0197   0.01   0.00
     s   0.0394   0.01   0.08
     c   1.1646   0.11   0.00

March 11, 201788108 MHz