In this note, I want to discuss a pair of long-boom LPDA designs to cover all of the amateur bands from 20 through 10 meters. Long-boom means (for our purposes) anything over 45' or so. We know that 5-6-element monoband Yagis can achieve a little over 10.1 dBi free-space gain with better than 20 dB front-to-back ratios across 20 meters with boom lengths between 45 and 53 feet. The question before us is this: what can we achieve using a similar boom length in a multi-band antenna?
Standards of Comparison
In the tri-band category, Force 12 has a 49-foot model with excellent performance on 20, 15, and 10 meters. However, the standard for comparison for an LPDA would need to cover all 5 upper HF bands.
The only single-boom design with high performance on all 5 amateur bands is the ON4ANT forward-stagger design, which has recently appeared in journals and also appears at my web site. Fig. 1 shows the general outline of the "final" 14-element, 60'-boom model designed by Johan Van de Velde.
For each band below 10 meters, the director also serves as the reflector for the next higher band. As well, for all bands above 20 meters, the director serves as the reflector for the next higher band. Additional directors have been added to improve 10-meter performance.
For reference, the following EZNEC-4 model description will provide the dimensions (in meters):
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ON4ANT 5-b Yagi: 14-28 Final Frequency = 14.175 MHz.
Wire Loss: Aluminum -- Resistivity = 4E-08 ohm-m, Rel. Perm. = 1
--------------- WIRES ---------------
Wire Conn. --- End 1 (x,y,z : m ) Conn. --- End 2 (x,y,z : m ) Dia(mm) Segs
1 -5.450, 0.000, 0.000 5.450, 0.000, 0.000 3.20E+01 37
2 -5.200, 2.000, 0.000 5.200, 2.000, 0.000 3.20E+01 35
3 -4.900, 3.600, 0.000 4.900, 3.600, 0.000 3.20E+01 34
4 -4.150, 5.250, 0.000 4.150, 5.250, 0.000 2.50E+01 28
5 -4.020, 6.400, 0.000 4.020, 6.400, 0.000 2.50E+01 27
6 -3.800, 7.200, 0.000 3.800, 7.200, 0.000 2.50E+01 25
7 -3.395, 8.400, 0.000 3.395, 8.400, 0.000 2.50E+01 23
8 -3.020, 9.500, 0.000 3.020, 9.500, 0.000 2.50E+01 21
9 -2.910, 10.800, 0.000 2.910, 10.800, 0.000 2.50E+01 21
10 -2.680, 12.000, 0.000 2.680, 12.000, 0.000 2.30E+01 19
11 -2.550, 13.014, 0.000 2.550, 13.014, 0.000 2.30E+01 19
12 -2.470, 13.816, 0.000 2.470, 13.816, 0.000 2.30E+01 17
13 -2.440, 15.775, 0.000 2.440, 15.775, 0.000 2.30E+01 16
14 -2.310, 18.250, 0.000 2.310, 18.250, 0.000 2.30E+01 16
-------------- SOURCES --------------
Source Wire Wire #/Pct From End 1 Ampl.(V, A) Phase(Deg.) Type
Seg. Actual (Specified)
1 18 2 / 50.00 ( 2 / 50.00) 1.000 0.000 I
No loads specified
No transmission lines specified
Ground type is Free Space
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
More important is the performance potential, which the following table reveals:
Freq. Gain F-B Feed Impedance MHz dBi dB R +/- jX Ohms 20 14.0 8.30 36.74 28.8 - j 0.4 14.175 8.41 27.35 24.7 + j 7.9 14.35 8.55 20.57 19.0 + j18.8 17 18.118 8.35 23.06 31.7 - j 4.9 15 21.0 8.73 23.12 34.1 + j 2.0 21.225 8.86 23.15 35.9 + j10.3 21.45 8.99 23.04 37.4 + j18.6 12 24.94 9.70 37.50 23.4 + j14.6 10 28.0 9.92 26.58 30.0 - j 8.8 28.35 9.99 39.15 33.5 - j 4.7 28.7 9.69 34.30 20.3 - j12.2
Because elements must do double duty, performance improves with frequency. Even the 20-meter performance improves as one moves up the band, since the 20-meter director must be cut and positioned also to serve as the 17-meter reflector. 15 meters shows a similar pattern. The 180-degree front-to-back value exceeds 20 dB throughout the passband.
No SWR figures appear since the antenna's 5 feedpoints (one for each band) are designed for use with a gamma match. The significant limitation (from the perspective of broadband design, but not from the perspective of some kinds of operating interests) is the "cut-off" of 10-meter coverage somewhere between 28.7 and 28.8 MHz, as gain continues to decrease and the feedpoint resistive component of the impedances continues to decrease.
The ON4ANT design makes a good standard against which to compare a high-performance LPDA.
Version 1: Circular-Tau-Modified Standard LPDA Design
The initial version of the LPDA uses a Tau of 0.95 and a Sigma of 0.056. Ideally, one should use a Tau of 0.96 and an optimized Sigma somewhat higher than 0.18. However, the boom length for such an antenna becomes well over 3 times the length of the present design. With the Tau and Sigma values given, the boom length is about 51.5' with 21 elements, all of which are uniformly 0.5" in diameter. Fig. 2 shows the general outline of the array.
For reference and element dimensions (in inches), the EZNEC model description follows:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14-30 MHz .95/.056 21 el 51.5' Frequency = 14 MHz.
Wire Loss: Aluminum -- Resistivity = 4E-08 ohm-m, Rel. Perm. = 1
--------------- WIRES ---------------
Wire Conn. --- End 1 (x,y,z : in) Conn. --- End 2 (x,y,z : in) Dia(in) Segs
1 0.000,-216.30, 0.000 0.000,216.300, 0.000 5.00E-01 25
2 48.177,-205.00, 0.000 48.177,205.000, 0.000 5.00E-01 23
3 93.944,-194.00, 0.000 93.944,194.000, 0.000 5.00E-01 23
4 137.424,-184.40, 0.000 137.424,184.399, 0.000 5.00E-01 21
5 178.729,-175.18, 0.000 178.729,175.179, 0.000 5.00E-01 21
6 217.969,-166.42, 0.000 217.969,166.420, 0.000 5.00E-01 19
7 255.248,-158.10, 0.000 255.248,158.099, 0.000 5.00E-01 19
8 290.662,-150.19, 0.000 290.662,150.194, 0.000 5.00E-01 17
9 324.306,-142.68, 0.000 324.306,142.685, 0.000 5.00E-01 17
10 356.267,-135.55, 0.000 356.267,135.550, 0.000 5.00E-01 15
11 386.630,-128.77, 0.000 386.630,128.773, 0.000 5.00E-01 15
12 415.475,-122.33, 0.000 415.475,122.334, 0.000 5.00E-01 15
13 442.878,-116.22, 0.000 442.878,116.217, 0.000 5.00E-01 13
14 468.911,-110.41, 0.000 468.911,110.407, 0.000 5.00E-01 13
15 493.642,-104.89, 0.000 493.642,104.886, 0.000 5.00E-01 13
16 517.136,-99.642, 0.000 517.136, 99.642, 0.000 5.00E-01 11
17 539.456,-94.660, 0.000 539.456, 94.660, 0.000 5.00E-01 11
18 560.660,-89.927, 0.000 560.660, 89.927, 0.000 5.00E-01 11
19 580.804,-85.431, 0.000 580.804, 85.431, 0.000 5.00E-01 9
20 599.940,-81.159, 0.000 599.940, 81.159, 0.000 5.00E-01 9
21 618.120,-77.101, 0.000 618.120, 77.101, 0.000 5.00E-01 9
-------------- SOURCES --------------
Source Wire Wire #/Pct From End 1 Ampl.(V, A) Phase(Deg.) Type
Seg. Actual (Specified)
1 5 21 / 50.00 ( 21 / 50.00) 0.707 0.000 V
No loads specified
-------- TRANSMISSION LINES ---------
Line Wire #/% From End 1 Wire #/% From End 1 Length Z0 Vel Rev/
Actual (Specified) Actual (Specified) Ohms Fact Norm
1 1/50.0 ( 1/50.0) 2/50.0 ( 2/50.0) Actual dist 100.0 1.00 R
2 2/50.0 ( 2/50.0) 3/50.0 ( 3/50.0) Actual dist 100.0 1.00 R
3 3/50.0 ( 3/50.0) 4/50.0 ( 4/50.0) Actual dist 100.0 1.00 R
4 4/50.0 ( 4/50.0) 5/50.0 ( 5/50.0) Actual dist 100.0 1.00 R
5 5/50.0 ( 5/50.0) 6/50.0 ( 6/50.0) Actual dist 100.0 1.00 R
6 6/50.0 ( 6/50.0) 7/50.0 ( 7/50.0) Actual dist 100.0 1.00 R
7 7/50.0 ( 7/50.0) 8/50.0 ( 8/50.0) Actual dist 100.0 1.00 R
8 8/50.0 ( 8/50.0) 9/50.0 ( 9/50.0) Actual dist 100.0 1.00 R
9 9/50.0 ( 9/50.0) 10/50.0 ( 10/50.0) Actual dist 100.0 1.00 R
10 10/50.0 ( 10/50.0) 11/50.0 ( 11/50.0) Actual dist 100.0 1.00 R
11 11/50.0 ( 11/50.0) 12/50.0 ( 12/50.0) Actual dist 100.0 1.00 R
12 12/50.0 ( 12/50.0) 13/50.0 ( 13/50.0) Actual dist 100.0 1.00 R
13 13/50.0 ( 13/50.0) 14/50.0 ( 14/50.0) Actual dist 100.0 1.00 R
14 14/50.0 ( 14/50.0) 15/50.0 ( 15/50.0) Actual dist 100.0 1.00 R
15 15/50.0 ( 15/50.0) 16/50.0 ( 16/50.0) Actual dist 100.0 1.00 R
16 16/50.0 ( 16/50.0) 17/50.0 ( 17/50.0) Actual dist 100.0 1.00 R
17 17/50.0 ( 17/50.0) 18/50.0 ( 18/50.0) Actual dist 100.0 1.00 R
18 18/50.0 ( 18/50.0) 19/50.0 ( 19/50.0) Actual dist 100.0 1.00 R
19 19/50.0 ( 19/50.0) 20/50.0 ( 20/50.0) Actual dist 100.0 1.00 R
20 20/50.0 ( 20/50.0) 21/50.0 ( 21/50.0) Actual dist 100.0 1.00 R
Ground type is Free Space
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
As one decreases the characteristic impedance of the phasing line from 200 Ohms downward, the array draws closer to having an acceptable 50-Ohm or 75-Ohm SWR throughout its passband (14-30 MHz). However, these same reductions often reveal frequencies at which an LPDA will show a weakness. A weakness means that the elements to the rear of the element with the highest current magnitude begin to operate in a harmonic mode. The result is a reduction in forward gain and a very significant reduction in front-to-back ratio. In short, rearward radiation becomes quite large at frequencies of weakness. The design uses a 100-Ohm phase line, which is physically practical for either double boom construction or for a separate phase line structure. The array shows potential weaknesses at about 19.75 MHz and again at 26.5 MHz. Since these frequencies lie between amateur bands, no compensatory treatments were applied.
To enhance performance in the upper HF region, the forward elements were subjected to circularization, a process of decreasing the value of Tau with respect to be element length and spacing for the affected elements. The result was a small increase in upper HF gain, but a more useful improvement in the feedpoint SWR curve.
The following table provides the potential performance figures for the NEC-4 model:
Freq. Gain F-B Feed Impedance 50-Ohm 75-Ohm MHz dBi dB R +/- jX Ohms VSWR VSWR 20 14.0 8.82 25.45 75.0 + j 0.1 1.50 1.00 14.175 8.82 31.25 73.9 - j 2.9 1.48 1.04 14.35 8.78 42.54 72.5 - j 6.3 1.47 1.10 17 18.118 8.74 40.48 69.1 - j 7.6 1.42 1.14 15 21.0 8.52 34.31 60.6 + j 1.3 1.21 1.24 21.225 8.50 34.54 65.9 + j 4.2 1.33 1.15 21.45 8.50 34.73 71.3 + j 1.4 1.43 1.06 12 24.94 8.39 32.03 61.7 - j 8.9 1.28 1.25 10 28.0 8.00 25.31 66.6 - j16.8 1.50 1.30 28.5 8.05 26.38 54.1 - j 3.3 1.11 1.39 29.0 7.97 25.35 73.6 - j 0.8 1.47 1.02 29.5 7.79 23.27 63.6 - j30.7 1.80 1.60
As the frequency approaches 30 MHz, the 75-Ohm VSWR exceed 2:1 by a small amount, although the 50-Ohm SWR remains at about 1.8:1. The feedpoint resistance begins to sink rapidly above 29.5 MHz.
Below 15 meters, the gain performance of the LPDA exceeds the ON4ANT forward-stagger Yagi. More generally, the LPDA front-to-back ratio is more stable, as it tracks the gain of the antenna at each frequency. 10-meter performance is down considerably relative to the Yagi. This phenomenon is quite normal for an LPDA where the upper design frequency is less than 1.6 times the highest frequency used. Adding further elements (to a self-resonant frequency of about 50 MHz) would have significantly lengthened the boom. At least 5 further elements would have been required.
The reduction in gain (and front-to-back) at higher frequencies stems in large measure from the fact that in a wide-band LPDA array, all of the elements forward of the one with the highest current magnitude at a given frequency are active, essentially adding many "directors" to the array. As we increase frequency, the element with the highest current magnitude moves forward, leaving fewer elements to serve as "directors." Circularizing the value of Tau for the forward-most elements can improve the upper-end gain, but it cannot fully compensate for all of the reduction.
As a consequence of the gain fall-off, further design was undertaken.
Version 2: Circular-Tau-Modified Standard LPDA Design With a Parasitic Director
I added a director to the array, as shown in Fig. 3. The director adds only 4.3' to the boom length, but equalizes performance at both ends of the passband.
The resulting array is described in EZNEC-4 terms:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14-30 MHz .95/.056 21+dir 55.8' Frequency = 14 MHz.
Wire Loss: Aluminum -- Resistivity = 4E-08 ohm-m, Rel. Perm. = 1
--------------- WIRES ---------------
Wire Conn. --- End 1 (x,y,z : in) Conn. --- End 2 (x,y,z : in) Dia(in) Segs
1 0.000,-216.30, 0.000 0.000,216.300, 0.000 5.00E-01 25
2 48.177,-205.00, 0.000 48.177,205.000, 0.000 5.00E-01 23
3 93.944,-194.00, 0.000 93.944,194.000, 0.000 5.00E-01 23
4 137.424,-184.40, 0.000 137.424,184.399, 0.000 5.00E-01 21
5 178.729,-175.18, 0.000 178.729,175.179, 0.000 5.00E-01 21
6 217.969,-166.42, 0.000 217.969,166.420, 0.000 5.00E-01 19
7 255.248,-158.10, 0.000 255.248,158.099, 0.000 5.00E-01 19
8 290.662,-150.19, 0.000 290.662,150.194, 0.000 5.00E-01 17
9 324.306,-142.68, 0.000 324.306,142.685, 0.000 5.00E-01 17
10 356.267,-135.55, 0.000 356.267,135.550, 0.000 5.00E-01 15
11 386.630,-128.77, 0.000 386.630,128.773, 0.000 5.00E-01 15
12 415.475,-122.33, 0.000 415.475,122.334, 0.000 5.00E-01 15
13 442.878,-116.22, 0.000 442.878,116.217, 0.000 5.00E-01 13
14 468.911,-110.41, 0.000 468.911,110.407, 0.000 5.00E-01 13
15 493.642,-104.89, 0.000 493.642,104.886, 0.000 5.00E-01 13
16 517.136,-99.642, 0.000 517.136, 99.642, 0.000 5.00E-01 11
17 539.456,-94.660, 0.000 539.456, 94.660, 0.000 5.00E-01 11
18 560.660,-89.927, 0.000 560.660, 89.927, 0.000 5.00E-01 11
19 580.804,-85.431, 0.000 580.804, 85.431, 0.000 5.00E-01 9
20 599.940,-81.159, 0.000 599.940, 81.159, 0.000 5.00E-01 9
21 618.120,-77.101, 0.000 618.120, 77.101, 0.000 5.00E-01 9
22 670.000,-88.700, 0.000 670.000, 88.700, 0.000 5.00E-01 11
-------------- SOURCES --------------
Source Wire Wire #/Pct From End 1 Ampl.(V, A) Phase(Deg.) Type
Seg. Actual (Specified)
1 5 21 / 50.00 ( 21 / 50.00) 0.707 0.000 V
No loads specified
-------- TRANSMISSION LINES ---------
Line Wire #/% From End 1 Wire #/% From End 1 Length Z0 Vel Rev/
Actual (Specified) Actual (Specified) Ohms Fact Norm
1 1/50.0 ( 1/50.0) 2/50.0 ( 2/50.0) Actual dist 100.0 1.00 R
2 2/50.0 ( 2/50.0) 3/50.0 ( 3/50.0) Actual dist 100.0 1.00 R
3 3/50.0 ( 3/50.0) 4/50.0 ( 4/50.0) Actual dist 100.0 1.00 R
4 4/50.0 ( 4/50.0) 5/50.0 ( 5/50.0) Actual dist 100.0 1.00 R
5 5/50.0 ( 5/50.0) 6/50.0 ( 6/50.0) Actual dist 100.0 1.00 R
6 6/50.0 ( 6/50.0) 7/50.0 ( 7/50.0) Actual dist 100.0 1.00 R
7 7/50.0 ( 7/50.0) 8/50.0 ( 8/50.0) Actual dist 100.0 1.00 R
8 8/50.0 ( 8/50.0) 9/50.0 ( 9/50.0) Actual dist 100.0 1.00 R
9 9/50.0 ( 9/50.0) 10/50.0 ( 10/50.0) Actual dist 100.0 1.00 R
10 10/50.0 ( 10/50.0) 11/50.0 ( 11/50.0) Actual dist 100.0 1.00 R
11 11/50.0 ( 11/50.0) 12/50.0 ( 12/50.0) Actual dist 100.0 1.00 R
12 12/50.0 ( 12/50.0) 13/50.0 ( 13/50.0) Actual dist 100.0 1.00 R
13 13/50.0 ( 13/50.0) 14/50.0 ( 14/50.0) Actual dist 100.0 1.00 R
14 14/50.0 ( 14/50.0) 15/50.0 ( 15/50.0) Actual dist 100.0 1.00 R
15 15/50.0 ( 15/50.0) 16/50.0 ( 16/50.0) Actual dist 100.0 1.00 R
16 16/50.0 ( 16/50.0) 17/50.0 ( 17/50.0) Actual dist 100.0 1.00 R
17 17/50.0 ( 17/50.0) 18/50.0 ( 18/50.0) Actual dist 100.0 1.00 R
18 18/50.0 ( 18/50.0) 19/50.0 ( 19/50.0) Actual dist 100.0 1.00 R
19 19/50.0 ( 19/50.0) 20/50.0 ( 20/50.0) Actual dist 100.0 1.00 R
20 20/50.0 ( 20/50.0) 21/50.0 ( 21/50.0) Actual dist 100.0 1.00 R
Ground type is Free Space
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The parasitic director length and position represent a design compromise. Further gain is achievable, but at the cost of unacceptable 10-meter SWR values. A parasitic element also decreases the front-to-back ratio at upper frequencies of the passband. The design goals included a front-to-back ratio at 29.5 MHz of at least 20 dB plus a 50-Ohm SWR no higher than 2:1 across 10 meters. The following performance table reveals that both objectives were met.
Freq. Gain F-B Feed Impedance 50-Ohm 75-Ohm MHz dBi dB R +/- jX Ohms VSWR VSWR 20 14.0 8.85 24.83 75.6 + j 0.2 1.51 1.01 14.175 8.85 30.27 74.2 - j 3.5 1.49 1.05 14.35 8.81 38.97 71.9 - j 6.5 1.46 1.10 17 18.118 8.83 38.07 67.2 - j 6.9 1.38 1.16 15 21.0 8.72 42.38 64.8 + j 0.1 1.30 1.16 21.225 8.71 41.41 66.9 - j 0.6 1.34 1.12 21.45 8.72 40.76 67.1 - j 1.8 1.34 1.12 12 24.94 8.81 32.04 73.6 - j 2.4 1.48 1.04 10 28.0 8.92 24.94 72.3 + j16.5 1.58 1.26 28.5 9.02 22.35 82.3 - j31.3 1.99 1.50 29.0 9.04 20.97 39.6 - j22.4 1.73 2.12 29.5 9.04 20.03 38.7 + j 8.8 1.38 1.97
Although the LPDA does not achieve all of the upper-end gain of the ON4ANT Yagi, it does achieve a remarkably smooth free-space gain curve with only about 0.3 dB variation across the entire passband of the array.
Some Comparisons
In order to assess the full potential of the LPDA arrays, I performed frequency sweeps of them in 0.25 MHz increments from 13 through 31 MHz. The following graphics are very nearly self-explanatory. Except where values on the tables above coincide with frequency markers in the graphs below, expect to find very slight differences in values, since all properties of an LPDA undulate across the passband.
Fig. 4 shows the free-space gain curve of the arrays in dBi. Note the frequencies (19.75 MHz and 26.5 MHz) at which the gain shows an abnormal decrease. If one wishes to eliminate these dips, then the weakness can be suppressed with a single stub on the lower frequency element that shows the highest harmonic mode operation.
The graph also shows performance deterioration at both upper and lower ends of the band, except for the gain on the version with the director. However, that increasing high frequency gain will be offset by decreases in the front-to-back ratio.
The most significant feature of the gain curve is a revelation of the effects of the parasitic director. The director improves gain (although insignificantly so) even at the lowest design frequency of the array. Given the current magnitude on it, the director must be considered an active element through the design spectrum.
The 180-degree front-to-back curve, shown in Fig. 5, shows far more variation than the gain curve relative to the two array designs. However, the "unnatural" dips in the front-to-back ratio reach their lowest values at same frequencies as the gain dip minima: 19.75 MHz and 26.5 MHz. In actuality, the minima occur at very slightly different frequencies. The peaks and nulls in the undulating gain and front-to-back curves do not exactly coincide.
Above 20 MHz, the presence of the director most significantly alters the front-to-back performance of the array, shifting the overall curve so that the peaks are lower in frequency relative to the version without the director. As well, above 28 MHz, the array with the director shows a much more rapid drop in front-to-back ratio. The overall front-to-back curve can be altered further with changes in director length and spacing. However, balancing goals for gain, front-to-back ratio, feedpoint impedance, and overall boom length require a design compromise. The closer the spacing of the director to the forward LPDA element, the more radical its effect upon performance at the upper end of the passband.
Fig. 6 shows 2 pairs of SWR curves, with 50-Ohm curves and 75-Ohm curves shown for each version of the array. To distinguish the designs, in the legend, "ND" means "no director," and "D" means "director." Despite the fact the impedance values seem to track a 75-Ohm impedance center across most of the passband, a 50-Ohm feedline appears to be the better choice at the passband edges. Both versions of the LPDA show a 50-Ohm 2:1 SWR or better from 14 through 29.7 MHz.
Conclusion
The Director-LPDA offers somewhat better low-end performance but slightly inferior high-end performance relative to the ON4ANT Yagi. However, the LPDA 10-meter performance extends across the entire band. The LPDA has the advantage of requiring only a single feedline. However, it does require the construction of a phasing line and element-to-boom insulating plates for all elements. Of course, the LPDA is usable at all frequencies between 14 and 30 MHz (with a corrective for the weaknesses noted). Even with a director, the array is 4' shorter than the "final" forward-stagger Yagi.
Although the design employs a value for Tau (0.95) close to the maximum recommended value, the array does not achieve all of its potential gain. With the use of an optimized value for Sigma (rather than the 0.056 value actually used in the design), free-space gain would increase to a maximum close to 11.5 dBi, with some front-to-back (and averaged front-to-rear) figures exceeding 50 dB. As noted initially, however, such an array would require 3 to 4 times the boom length.
The LPDA with no director is not so inferior to the director array that it should be ignored. At a height of 70' or so, the gain of the array across the entire passband is remarkably equal, allowing for the lowering of the take-off angle with increasing frequency. There is under 0.4 dB difference in maximum among 14, 21, and 28 MHz values.
At present, these LPDA arrays are design exercises, since I lack the facilities to construct and the robust tower and rotator to support a long-boom LPDA. Therefore, I shall not include potential mechanical design considerations in these notes. However, the arrays are samples of what an LPDA can do within the limitations of what amateurs consider to be long-boom antennas. Although the long-boom LPDA presents mechanical challenges, it achieves performance competitive with stacks of 2 ordinary multi-band Yagis without the extended mast. In short, it is one more option within the amateur arsenal of high performance multi-band arrays.
Note: The purpose of this article is to disseminate information and ideas. The author retains all design rights associated with the subject arrays, including modifications for improved performance over standard arrays of a similar type and including all reasonable variations upon them both stated or implied by the text or the designs themselves.
Updated 07-01-2001. © L. B. Cebik, W4RNL. The original item appeared in AntenneX for June, 2001. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.
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