Körner 19.3

Peter Körner in Lund, Sweden, designed this Yagi array. It has a boom length of 5.1 m (201″), 19 elements, five reflectors, a horizontal folded dipole, and uses a halfwave coaxial balun.

Unlike log-Yagis, the 19.3 has no phasing lines that can pick up current from the boom and degrade the pattern.

This overhead view shows the horizontal folded dipole. It is unusually long and the two conductor currents differ, as does their coupling to the first director. Because of these factors, conductor spacing strongly affects antenna performance and can be optimized. It provides only a weak degree of freedom for a vertical folded dipole.

This shows the antenna under test at ground level. The boom is not reinforced.

Here the antenna with boom reinforcement is temporarily installed well above ground for testing with broadcast signals. Peter has some concern that the mast may interact with nearby elements. An offset mast can disrupt fields in a way a centered boom cannot.

This shows how the 15 mm × 5 mm folded dipole conductors join at the ends. The element mount on the right is a repurposed support for 10 mm hydraulic fluid lines.

Modeling Results

I modeled the antenna with the AO 9.65 Antenna Optimizer program using 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     318 + j23    1.10     0.01      0.01      8.77      32.56
    89     328 + j16    1.11     0.01      0.01      8.94      35.30
    90     333 + j7     1.11     0.01      0.01      9.11      37.42
    91     335 - j1     1.12     0.01      0.01      9.29      38.27
    92     332 - j8     1.11     0.01      0.01      9.47      38.30
    93     326 - j12    1.10     0.01      0.01      9.66      38.42
    94     320 - j12    1.08     0.01      0.01      9.84      37.56
    95     313 - j10    1.05     0.00      0.01     10.02      36.90
    96     307 - j4     1.03     0.00      0.01     10.20      36.53
    97     304 + j3     1.02     0.00      0.02     10.36      36.44
    98     302 + j10    1.04     0.00      0.02     10.50      36.19
    99     300 + j17    1.06     0.00      0.02     10.62      35.72
   100     296 + j27    1.09     0.01      0.02     10.70      34.81
   101     294 + j38    1.14     0.02      0.03     10.74      34.07
   102     298 + j51    1.18     0.03      0.03     10.71      33.67
   103     309 + j58    1.21     0.04      0.04     10.62      33.41
   104     316 + j49    1.18     0.03      0.05     10.48      33.33
   105     295 + j42    1.15     0.02      0.06     10.27      34.54
   106     287 + j77    1.30     0.08      0.08      9.97      33.73
   107     357 + j52    1.27     0.06      0.12      9.77      32.70
   108     295 + j23    1.08     0.01      0.20      9.50      30.55

Ground Effects

This shows how ground proximity affects F/R at 1° elevation angle for various antenna heights.

Antenna File

Körner 19.3 Yagi
Free Space Symmetric
88 93 98 103 108 MHz
22 6061-T6 wires, meters
h1 = .315	; reflector heights
h2 = .73
rp0 = -.024	; reflector positions
rp1 = -.012
rp2 = .05
de1 = .47	; driven element positions
de2 = .54
p1 = .64	; director positions
p2 = .752
p3 = .945
p4 = 1.11
p5 = 1.374
p6 = 1.612
p7 = 1.844
p8 = 2.272
p9 = 2.788
p10 = 3.256
p11 = 3.83
p12 = 4.377
p13 = 5.08
r0 = 1.003	; reflector half-lengths
r1 = 1.003
r2 = .96
de = .822	; driven element half-length
d1 = .662	; director half-lengths
d2 = .672
d3 = .657
d4 = .64
d5 = .633
d6 = .617
d7 = .611
d8 = .629
d9 = .602
d10 = .606
d11 = .616
d12 = .619
d13 = .574
1  rp2  -r2 -h2   rp2  r2 -h2   .01		; reflectors
1  rp1  -r1 -h1   rp1  r1 -h1   .01
1  rp0  -r0   0   rp0  r0   0   .01
1  rp1  -r1  h1   rp1  r1  h1   .01
1  rp2  -r2  h2   rp2  r2  h2   .01
1  de1  -de   0   de1  de   0   .01148		; driven element
1  de2  -de   0   de2  de   0   .01148
1  de1  -de   0   de2 -de   0   .015
1  de1   de   0   de2  de   0   .015
1   p1  -d1   0    p1  d1   0   .01		; directors
1   p2  -d2   0    p2  d2   0   .01
1   p3  -d3   0    p3  d3   0   .01
1   p4  -d4   0    p4  d4   0   .01
1   p5  -d5   0    p5  d5   0   .01
1   p6  -d6   0    p6  d6   0   .01
1   p7  -d7   0    p7  d7   0   .01
1   p8  -d8   0    p8  d8   0   .01
1   p9  -d9   0    p9  d9   0   .01
1  p10 -d10   0   p10 d10   0   .01
1  p11 -d11   0   p11 d11   0   .01
1  p12 -d12   0   p12 d12   0   .01
1  p13 -d13   0   p13 d13   0   .01
1 source
Wire 7, center

The 11.48 mm diameters are cylindrical equivalents of the 15 mm × 5 mm rectangular folded dipole conductors. The 15 mm conductors are short tubes that connect the folded dipole ends.

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
    h1   0.0010   0.00   0.01
    h2   0.0010   0.00   0.03
   rp0   0.0010   0.00   0.01
   rp1   0.0010   0.00   0.01
   rp2   0.0010   0.00   0.02
   de1   0.0010   0.00   0.04
   de2   0.0010   0.01   0.04
    p1   0.0010   0.01   0.04
    p2   0.0010   0.01   0.09
    p3   0.0010   0.00   0.05
    p4   0.0010   0.00   0.02
    p5   0.0010   0.00   0.02
    p6   0.0010   0.00   0.03
    p7   0.0010   0.00   0.03
    p8   0.0010   0.00   0.05
    p9   0.0010   0.00   0.04
   p10   0.0010   0.00   0.03
   p11   0.0010   0.00   0.03
   p12   0.0010   0.00   0.06
   p13   0.0010   0.00   0.03
    r0   0.0005   0.00   0.02
    r1   0.0005   0.00   0.03
    r2   0.0005   0.00   0.03
    de   0.0005   0.00   0.01
    d1   0.0005   0.00   0.03
    d2   0.0005   0.02   0.16
    d3   0.0005   0.01   0.22
    d4   0.0005   0.00   0.05
    d5   0.0005   0.00   0.05
    d6   0.0005   0.00   0.02
    d7   0.0005   0.00   0.05
    d8   0.0005   0.02   0.15
    d9   0.0005   0.00   0.04
   d10   0.0005   0.01   0.07
   d11   0.0005   0.01   0.07
   d12   0.0005   0.01   0.14
   d13   0.0005   0.00   0.03

Measurements

This is the SWR curve measured with an HP 8714B network analyzer.

Peter measured F/B in a city environment. He used a Promax spectrum monitor on horizontally polarized broadcast signals from Sweden and Germany. The following table compares F/B calculated by NEC-2 at 50 segments/halfwave with the measured values.

 Freq  Calculated  Measured    Transmitter     Distance           Notes
  MHz    F/B dB     F/B dB       Location         km
 87.7      32         42         Halmstad        121
 87.9      33         28           Malmö          17
 91.2      39         25         Halmstad        121       Possible interference
 93.3      41         29           Malmö          17
 95.4      44         34         Halmstad        121
 97.3      41         37         Halmstad        121
 98.0      39         28           Malmö          17
100.6      34         32           Malmö          17
102.0      34         33           Malmö          17
104.8      38       30-33         Marlow         175       Varying signal level, slight interference
105.8      36       31-34      Helpterberg       248       Varying signal level

Calculated and measured values may differ due to modeling limitations, construction tolerances, balun or feedline pickup, coupling to nearby conductors, reflection from distant structures, ground effects, interfering signals, or varying signal levels. Peter notes that F/B for the Halmstad signals degraded some 10 dB when he turned the antenna 10°–15° to the west.

This is the view toward Malmö from the antenna location about 20 m above ground.

The opposite direction. I'm surprised Peter was able to measure such high F/B values with so many potential reflections.

A shadow I spotted in one high-resolution skyline photo. Peter secures himself with a safety rope while working on the steeply pitched roof.

Gallery

This is Peter's 19.3 installed 20 m above ground in Lund, Sweden. The guy lines are nonconductive.

Kay Richter built this 19.3 in Wittenberg, Germany.

Ralf Kronen's 19.3 has too much company in Viersen-Süchteln, Germany.

Thomas Nickel erected this 19.3 in Suhl, Germany.

David Pommerenke used braces instead of a secondary boom for his 19.3 in Rolla, Missouri. The antenna uses half-inch elements with compensated lengths.

Konrad Kosmatka used boom guys for his 19.3 in Plock, Poland. It rotates here. It vibrates here.

Olaf Panke used both boom guys and a secondary boom for his 19.3 in Gülzow, Germany.

Petr Vozár tested his 19.3 at the OK2KJU radio club near Prerov, Czechia.

Alan Parysek erected this 19.3 in Skalbmierz, Poland. It rotates here.

This shows Aleksandr Vorona's 19.3 before final installation in Poltava, Ukraine.

Vladimir Doroshenko uses this vertically polarized 19.3 in Dnepropetrovsk, Ukraine.

Mike Fallon added a small vertically polarized Yagi to the boom of his 19.3 in Saltdean, East Sussex, England.

John Bunkfeldt built this well-braced 19.3 in Frankfort, New York.

This 19.3 belongs to Antonín Roll in Mariánské Lázně, Czechia.

A professional installer tightens a 19.3 in Prague, Czechia.

Optimized 19.3

I optimized the 19.3 to keep all backlobes at least 36 dB down over 88–108 MHz. The boom length and element count are unchanged. The reflector boom is slightly shorter and the reflectors are in line. I used a loop-coupled driven element that 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 75Ω feedpoint, indicated by the red dot.

Modeling Results

I modeled the antenna with the AO 9.65 Antenna Optimizer using 28 analysis segments per conductor halfwave. Forward gain includes mismatch and conductor losses and gain 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    74.3 + j3.3   1.05     0.00      0.02      8.73      36.01
    89    76.6 - j3.2   1.05     0.00      0.02      8.89      38.62
    90    76.7 - j7.8   1.11     0.01      0.02      9.04      37.65
    91    75.7 - j10.8  1.15     0.02      0.02      9.20      36.87
    92    75.0 - j12.4  1.18     0.03      0.02      9.37      36.41
    93    74.3 - j13.3  1.20     0.03      0.02      9.54      36.06
    94    73.7 - j14.1  1.21     0.04      0.02      9.71      36.01
    95    72.8 - j14.5  1.22     0.04      0.02      9.88      36.10
    96    72.3 - j14.7  1.22     0.04      0.02     10.04      36.47
    97    72.2 - j14.6  1.22     0.04      0.02     10.19      36.72
    98    72.1 - j14.7  1.23     0.05      0.02     10.33      37.17
    99    72.1 - j15.5  1.24     0.05      0.03     10.43      36.37
   100    71.4 - j17.1  1.27     0.06      0.03     10.49      36.22
   101    69.2 - j18.4  1.31     0.08      0.03     10.51      36.84
   102    65.3 - j17.6  1.33     0.09      0.04     10.47      37.13
   103    62.8 - j13.1  1.30     0.07      0.05     10.40      36.13
   104    65.4 - j7.5   1.19     0.03      0.06     10.28      36.00
   105    73.5 - j8.3   1.12     0.01      0.07     10.09      36.31
   106    72.1 - j17.5  1.27     0.06      0.09      9.83      36.01
   107    64.4 - j9.4   1.23     0.04      0.12      9.73      36.00
   108    81.1 + j16.3  1.25     0.05      0.20      9.62      36.00

Antenna File

Optimized 19.3
Free Space Symmetric
88 94 96 98 100 101 103 104 105 106 107 108 MHz
26 6061-T6 wires, meters
h1 = .28935592		; reflector heights
h2 = .6861281
rp0 = 0			; reflector positions
rp1 = 0
rp2 = 0
dep = .44926091		; driven element position
p1 = .5854994		; director positions
p2 = .70334772
p3 = .8863801
p4 = 1.0852649
p5 = 1.3765714
p6 = 1.6023626
p7 = 1.9761888
p8 = 2.424466
p9 = 2.8201262
p10 = 3.2340984
p11 = 3.7484955
p12 = 4.3339432
p13 = 5.104
r0 = 1.05974		; reflector half-lengths
r1 = 1.0085324
r2 = .9689596
de = .7908045		; driven element half-length
d1 = .6645802		; director half-lengths
d2 = .66993663
d3 = .6566396
d4 = .6498772
d5 = .63500324
d6 = .62352554
d7 = .6266686
d8 = .6125574
d9 = .59389821
d10 = .61041114
d11 = .6110288
d12 = .598251
d13 = .5361455
w = .082707171		; loop half-width
s = .05002148		; loop spacing from first director
p = p1 - s
1  rp2  -r2 -h2   rp2  r2 -h2   .01		; reflectors
1  rp1  -r1 -h1   rp1  r1 -h1   .01
1  rp0  -r0   0   rp0  r0   0   .01
1  rp1  -r1  h1   rp1  r1  h1   .01
1  rp2  -r2  h2   rp2  r2  h2   .01
1  dep    w   0   dep  de   0   .01148		; driven element
1  dep   -w   0   dep -de   0   .01148		; 11.48 mm is the cylindrical
8  dep   -w   0   dep   w   0   .01148		; equivalent of 15 mm x 5 mm
8    p   -w   0     p   w   0   .01148		; rectangular conductors
4    p    w   0   dep   w   0   .015
4    p   -w   0   dep  -w   0   .015
1   p1  -d1   0    p1  -w   0   .01		; directors
8   p1   -w   0    p1   w   0   .01
1   p1    w   0    p1  d1   0   .01
1   p2  -d2   0    p2  d2   0   .01
1   p3  -d3   0    p3  d3   0   .01
1   p4  -d4   0    p4  d4   0   .01
1   p5  -d5   0    p5  d5   0   .01
1   p6  -d6   0    p6  d6   0   .01
1   p7  -d7   0    p7  d7   0   .01
1   p8  -d8   0    p8  d8   0   .01
1   p9  -d9   0    p9  d9   0   .01
1  p10 -d10   0   p10 d10   0   .01
1  p11 -d11   0   p11 d11   0   .01
1  p12 -d12   0   p12 d12   0   .01
1  p13 -d13   0   p13 d13   0   .01
1 source
Wire 9, center
1 load
c = 11.196933		; series feedpoint capacitor
Wire 9, center c pF

Construction

Use 15 mm × 5 mm rectangular conductors for the driven element and loop front. Use 15 mm round tubes with a bolt inside for the loop sides. Measure dimensions between conductor centerlines. The loop must be in the element 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.

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
    h1   0.0010   0.00   0.01
    h2   0.0010   0.00   0.06
   rp0   0.0010   0.00   0.01
   rp1   0.0010   0.00   0.02
   rp2   0.0010   0.00   0.04
   dep   0.0010   0.01   0.10
    p1   0.0010   0.01   0.15
    p2   0.0010   0.01   0.22
    p3   0.0010   0.00   0.08
    p4   0.0010   0.00   0.06
    p5   0.0010   0.00   0.03
    p6   0.0010   0.00   0.05
    p7   0.0010   0.00   0.06
    p8   0.0010   0.00   0.07
    p9   0.0010   0.00   0.07
   p10   0.0010   0.00   0.10
   p11   0.0010   0.00   0.06
   p12   0.0010   0.00   0.08
   p13   0.0010   0.00   0.05
    r0   0.0005   0.00   0.02
    r1   0.0005   0.00   0.05
    r2   0.0005   0.00   0.04
    de   0.0005   0.00   0.03
    d1   0.0010   0.01   0.51
    d2   0.0005   0.05   1.25
    d3   0.0005   0.02   0.52
    d4   0.0005   0.01   0.19
    d5   0.0005   0.01   0.12
    d6   0.0005   0.00   0.05
    d7   0.0005   0.01   0.30
    d8   0.0005   0.00   0.36
    d9   0.0005   0.01   0.08
   d10   0.0005   0.00   0.40
   d11   0.0005   0.01   0.58
   d12   0.0005   0.00   0.68
   d13   0.0005   0.00   0.16
     w   0.0005   0.01   0.00
     s   0.0010   0.02   0.03
     c   1.1197   0.14   0.00

Performance Comparison

The 19.3 gain curve includes the loss of a halfwave coaxial balun.


January 31, 201788–108 MHz