Home Depot Yagi

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 ″ 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 9.67 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 75:300Ω balun. It does need a series capacitor at the feedpoint, but you can make it from the feedline coax.

Modeling Results

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

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 short lengths of ABS 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 an 11-pF capacitor to the other side. Alternatively, use 22 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.

You can make the capacitor from the feedline coax. Belden 1530A RG-6, for example, has a capacitance of 16.2 pF per foot. Split the shield 8316″ from the open end of the feedline to obtain 11 pF. Just above the split connect the shield to one side of the feedpoint gap. Just below the split connect it to the other side of the gap. Seal the split and open end against moisture. Secure the capacitor along the top of the loop with tie-wraps. Run it along the side that connects to the shield above the split.

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 one 10-pF or two 20-pF capacitors.

A driven element with lower performance but easier to make is a dipole bent at the center with each half angled 6.1 to the rear. Mount the halves on a small nonconducting plate attached to the boom with two conduit straps. Attach 75Ω coax with a current balun.

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 - Copper Elements, Bent DE
Free Space Symmetric
88 90 92.5 95 98 103 104 106 107 108 MHz
11 copper wires, inches
ang = 6.12358		; driven element angle
h = 14.76641		; reflector height
rp = 0		        ; element positions
dep = 15.62771
d1p = 19.60263
d2p = 28.74627
d3p = 44.88853
d4p = 56.65011
d5p = 75.52132
d6p = 94.80137
d7p = 122
r = 34.88235		; element half-lengths
de = 30.5611
d1 = 26.30843
d2 = 25.53338
d3 = 24.37232
d4 = 24.31104
d5 = 24.43217
d6 = 23.84356
d7 = 22.1099
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

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.

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

September 15, 201888108 MHz