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Hi-VHF 13El FD Yagi - Stellar Labs 30-2476

Hi-VHF 13-Element Folded Dipole Yagi, including 4 Reflector Rods, MCM Stellar Labs 30-2476,
analyzed using 4nec2. Dimensions were provided by user [majortom]:
https://imageevent.com/holl_ands/yagis/hivhf13elfdyagistellarlabs

HiVHF Raw Gain = 9.8 to 12.5 dBi, F/B & F/R Ratio = 15 to 25 to 17 dB [Good to Excellent]
and SWR (300-ohms) is Under 2.7 [Excellent].

That is 0.9 to 1.7 dB higher Gain and much better F/B & F/R on low Channels than S-L 30-2475 9-El FD Yagi, found here:
https://imageevent.com/holl_ands/yagis/hivhf9elfdyagistellarlabs





EVAL RESULTS SUMMARY:
Code:
Input file : HiVHF_Stellar-Labs_13El_FD_Yagi_majortom.nec
Freq sweeps: [(88, 2, 11), (174, 1.5, 39)]
Autosegmentation: NO

         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
   88.0   0.75 -14.10 120.29 97.7  -1.08 -1.08    79.55  1665.76 1.02 0.08
   90.0   0.74 -13.61 106.94 96.9  -1.23 -1.23   121.33  1946.28 1.02 0.08
   92.0   0.73 -13.13  95.28 96.2  -1.38 -1.38   195.24  2335.17 1.02 0.08
   94.0   0.69 -12.69  85.08 95.6  -1.55 -1.55   339.59  2909.29 1.02 0.08
   96.0   0.65 -12.26  76.18 95.1  -1.74 -1.74   666.64  3834.45 1.02 0.08
   98.0   0.60 -11.86  68.39 94.7  -1.95 -1.95  1611.00  5511.18 1.01 0.06
  100.0   0.52 -11.49  61.57 94.4  -2.18 -2.18  5708.17  8531.96 1.01 0.06
  102.0   0.42 -11.17  55.61 94.2  -2.43 -2.43 16534.50 -1565.84 1.01 0.06
  104.0   0.29 -10.88  50.39 94.2  -2.72 -2.72  5080.41 -7136.58 1.01 0.06
  106.0   0.15 -10.63  45.82 94.0  -3.02 -3.02  1911.32 -4747.98 1.01 0.06
  108.0  -0.03 -10.43  41.82 94.2  -3.37 -3.37  1006.38 -3395.74 1.01 0.06

  174.0   9.82   9.44  1.81  56.4  15.34  15.34  216.50  128.23 1.00  0.00
  175.5   9.89   9.52  1.79  56.0  15.85  15.85  232.41  140.92 1.00  0.00
  177.0   9.97   9.61  1.79  55.6  16.37  16.37  248.80  152.18 1.00  0.00
  178.5  10.04   9.68  1.78  55.3  16.89  16.89  265.47  161.95 1.00  0.00
  180.0  10.11   9.74  1.79  54.9  17.43  17.43  282.17  170.18 1.00  0.00
  181.5  10.19   9.82  1.79  54.5  18.01  18.01  298.60  176.92 1.00  0.00
  183.0  10.27   9.90  1.80  54.1  18.63  18.63  314.46  182.31 1.00  0.00
  184.5  10.36   9.98  1.81  53.6  19.33  19.33  329.47  186.60 1.00  0.00
  186.0  10.44  10.05  1.82  53.2  20.11  20.11  343.43  190.14 1.00  0.00
  187.5  10.54  10.14  1.83  52.8  21.02  21.02  356.24  193.37 1.00  0.00
  189.0  10.63  10.22  1.85  52.4  22.06  22.06  367.94  196.79 1.00  0.00
  190.5  10.73  10.30  1.88  51.9  23.32  23.32  378.73  200.91 1.00  0.00
  192.0  10.84  10.39  1.91  51.4  24.84  24.85  389.02  206.21 1.00  0.00
  193.5  10.95  10.47  1.95  51.0  24.74  26.78  399.38  213.09 1.00  0.00
  195.0  11.07  10.56  2.00  50.5  24.69  29.24  410.57  221.81 1.00  0.00
  196.5  11.19  10.64  2.06  50.0  24.69  32.31  423.52  232.43 1.00 -0.00
  198.0  11.31  10.70  2.13  49.3  24.74  34.77  439.36  244.79 1.00 -0.00
  199.5  11.44  10.77  2.22  48.7  24.83  33.32  459.41  258.36 1.00 -0.00
  201.0  11.58  10.84  2.31  47.9  24.97  29.95  485.15  272.03 1.00 -0.00
  202.5  11.71  10.90  2.41  47.3  25.13  27.03  518.18  283.89 1.00 -0.00
  204.0  11.84  10.95  2.51  46.6  24.73  24.73  559.88  290.67 1.00 -0.00
  205.5  11.97  11.02  2.59  45.9  22.91  22.91  610.58  287.28 1.00 -0.00
  207.0  12.09  11.10  2.65  45.2  21.45  21.45  667.76  266.57 1.00 -0.00
  208.5  12.19  11.18  2.68  44.6  20.26  20.26  723.24  220.84 1.00 -0.00
  210.0  12.29  11.30  2.65  43.9  19.32  19.32  760.99  147.16 1.00 -0.00
  211.5  12.37  11.45  2.55  43.4  18.58  18.58  761.43   55.84 1.00 -0.00
  213.0  12.43  11.64  2.39  42.8  18.03  18.03  715.26  -27.60 1.00 -0.00
  214.5  12.47  11.85  2.15  42.2  17.67  17.67  634.50  -76.55 1.00 -0.00
  216.0  12.49  12.07  1.87  41.7  17.48  17.48  544.17  -80.72 1.00 -0.00
Press any key to continue . . .
4nec2 File:
Code:
CM Hi-VHF 13-El. Folded Dipole Yagi incl. 4 Refl. Rods, 4nec2 by holl_ands, 3May2019
CM Stellar Labs 30-2476 measured by majortom.  Tubular or Square 3/4-in Alum. Boom.
CM Driven O.D.=0.375", Others O.D.=0.375", Alum. Elements on TOP of Boom.
CM Driven Element: 0.25-in above boom. ALL IN INCHES.  Boom Length=82.7" + Ends.
CM AUTOSEG(13), AGT=1.0, NO Errors or Warnings.
CM Boom Correction NOT NEEDED since Negligible at Hi-VHF.
CM
CMD--EVAL --auto-segmentation=0 --char-impedance=300 --num-cores=7
CMD--EVAL -s(88,2,11) -s(174,1.5,39) --total-gain --publish
CE
' Radius of Simulated Balun SOURCE Wire, Adjust for AGT=1.0: HiVHF=0.191
SY Rsrc=0.191
'
' Cumulative X-Coord. Element Spacings:
SY X1=0.0		
SY X2=10.75
SY X3=14.75
SY X4=21.75
SY X5=30.0
SY X6=39.25
SY X7=49.5
SY X8=59.75
SY X9=70.0
SY X10=80.25
'
' Element HALF Lengths [Rear-Most Reflector Rod, FD, 5 Directors:
SY HL1=36.8125/2
SY HL2=14.9375	' Same as 9-el Yagi
SY HL3=23.375/2
SY HL4=23.375/2
SY HL5=23.375/2
SY HL6=22.5/2
SY HL7=22.5/2
SY HL8=21.625/2
SY HL9=21.625/2
SY HL10=21.625/2
'
SY FW=3.375		' Distance between Folded Dipole Elements
SY F1=FW-0.875	' Distance between Center of Boom and Folded Dipole Element
SY Relem=0.375/2	' Radius (inches) for Passive Reflector & Director Elements
SY RACT=0.375/2    	' Radius (inches) for Driven Element
'
' Half-Lengths of four Reflector Rods [Total Lengths = 33.125-in Max]:
SY Yrr=35.8128/2
' Z-Coord of Inner and Outer Pairs of Reflector Rods:
SY Zi=9.375/2
SY Zo=Zi+9.0
'
' Driven  Second Element with SOURCE in middle segment
' Folded Dipole Element and interconnecting wires (rectangular vice rounded)
GW  2  13  X2   -HL2    -F1   X2    HL2   -F1    Rsrc
GW  3   1  X2    HL2   0.875  X2    HL2   -F1    RACT
GW  4   1  X2   -HL2   0.875  X2   -HL2   -F1    RACT
GW  5  13  X2   -HL2   0.875  X2    HL2   0.875  RACT
' 8 Passive Directors:
GW  6  13  X3   -HL3   0.625  X3    HL3   0.625  Relem
GW  7  11  X4   -HL4   0.625  X4    HL4   0.625  Relem
GW  8  11  X5   -HL5   0.625  X5    HL5   0.625  Relem
GW  9  11  X6   -HL6   0.625  X6    HL6   0.625  Relem
GW 10  11  X7   -HL7   0.625  X7    HL7   0.625  Relem
GW 11   9  X8   -HL8   0.625  X8    HL8   0.625  Relem
GW 12   9  X9   -HL9   0.625  X9    HL9   0.625  Relem
GW 13   9  X10  -HL10  0.625  X10   HL10  0.625  Relem
'
' FOUR REFLECTOR RODS:
GW 51  17   X1  -Yrr  0.625+Zi  X1  Yrr  0.625+Zi  Relem
GW 52  17   X1  -Yrr  0.625-Zi  X1  Yrr  0.625-Zi  Relem
GW 53  17   X1  -Yrr  0.625+Zo  X1  Yrr  0.625+Zo  Relem
GW 54  17   X1  -Yrr  0.625-Zo  X1  Yrr  0.625-Zo  Relem
'
GS	0	 0	0.0254	' CONVERT ABOVE FROM INCHES TO METERS FOR NEC
GE	0			' No Ground Plane
GN	-1			' Free Space
EK 0				' Enable Extended Kernel
LD 5 0 0 0 2.470e7    	' Aluminum Conductivity
EX 0 2 7 0 1 0     		' Simulated (Balun) SOURCE at Middle of GW2
'
' FR Freq Sweep choices in order of increasing calculation time (fm holl_ands):
' FR 0 0 0 0 470 0		' Fixed Freq
' FR 0 29 0 0 470 12	' Freq Sweep 470-806 every 12 MHz - OLD UHF BAND
' FR 0 34 0 0 410 12	' Freq Sweep 410-806 every 12 MHz - Even Wider Sweep
' FR 0 39 0 0 470 6		' Freq Sweep 470-698 every 6 MHz - PREFERRED FOR UHF
' FR 0 77 0 0 470 3		' Freq Sweep 470-698 every 3 MHz
' FR 0 153 0 0 470 1.5	' Freq Sweep 470-698 every 1.5 MHz
' FR 0 71 0 0 300 10	' Freq Sweep 300-1000 every 10 MHz - WIDEBAND SWEEP
' FR Hi-VHF choices:
' FR 0 25 0 0 192 1		' Freq Sweep 192-216 every 1 MHz (Special for F/B)
' FR 0 15 0 0 174 3		' Freq Sweep 174-216 every 3 MHz
FR 0 29 0 0 174 1.5		' Freq Sweep 174-216 every 1.5 MHz - PREFERRED
' FR 0 39 0 0 174 1.5	' Freq Sweep 174-231 every 1.5 MHz - SPECIAL
' FR 0 43 0 0 174 1		' Freq Sweep 174-216 every 1 MHz - Hi-Rez
' FR 0 26 0 0 150 6		' Freq Sweep 150-300 every 6 MHz - WIDEBAND SWEEP
' FR Lo-VHF choices:
' FR 0 19 0 0 54 3		' Frequency Sweep every 3 MHz for Ch2-6 + FM
' FR 0 35 0 0 54 1		' Frequency Sweep every 1 MHz for Ch2-6
' FR 0 36 0 0 75 1		' Frequency Sweep every 1 MHz for Ch5 + Ch6 + FM
' FR 0 28 0 0 54 6		' Wide Freq Sweep every 6 MHz for Ch2-13
' FR 0 64 0 0 54 12		' Super Wide Freq Sweep 54-810 every 12 MHz
' RP choices in order of increasing calculation time:
' RP 0 1 1 1510 90 90 1 1 0 0	' 1D Gain toward 0-deg Azimuth - SIDE GAIN
' RP 0 1 1 1510 90 0 1 1 0 0	' 1D Gain toward 90-deg Azimuth - FORWARD GAIN
' RP 0 1 1 1510 90 180 1 1 0 0	' 1D Gain toward 270-deg Azimuth - REVERSE GAIN
' RP 0 1 37 1510 90 0 1 5 0 0 	' 2D (Left only) Azimuthal Gain Slice
RP 0 1 73 1510 90 0 1 5 0 0 	' 2D Azimuthal Gain Slice - PREFERRED
' RP 0 73 1 1510 90 0 5 1 0 0 	' 2D Elevation Gain Slice
' RP 0 73 73 1510 90 0 5 5 0 0 	' 3D Lower Hemisphere reveals antenna (Fixed Freq)
' RP 0 285 73 1510 90 0 5 5 0 0	' 3D Full Coverage obscures antenna (Fixed Freq)
EN
 

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FYI: 4nec2 Results for my 4nec2 File is only slightly different than yours...most likely due to Segmentation differences. In 4nec2 under SETTINGS I selected "Auto segmentation", ran AGT Test at 198 MHz and then hit F8 key to reveal NEC2 RESULTS File. The GW Segmentation Numbers contained in THAT file were then copied into my 4nec2 File. Don't forget to Uncheck "Auto segmentation" when you are done.

I also see that you assumed "X1=.1875". I used "X1=0", since I assumed that all of your dimensions were Center-to-Center. Although minor, this also could have caused some very minor differences. Also note that Segmentation Number for ALL FOUR Reflector Rods SHOULD have been the SAME.
 

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Thank you Holl_ands. Yours always look so much cleaner :)

Yeah the zero reference didn't seem to make much difference.
when adjusting the model I had assumed, probably incorrectly, the X=0 reference was the end of the boom.
Didn't matter much at all like ya say.
Definitely the booms are made from 1/2" square aluminum (actually ~ 17 mm O.D.), not 3/4"...
 

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NEC2 Engine can't accurately model a thin boom, so it IGNORES it and (where needed) uses a Boom Correction instead. Although it MIGHT be significant for UHF Antennas, it can usuallly be ignored for Full-Band Hi-VHF Antennas.

Not much Directivity or Gain on Ch2-6, more to the Rear and mostly negative on low Channels....but excessive SWR, which may or may not be a problem. However, S-L uses a Balun Box, which MAY contain a modern PCB (Printed Circuit Board) Balun...which would Attenuate Ch2-6 and change SWR to some Unknown degrees....or MAY contain a conventional Transformer type Balun,, which would NOT Attenuate Ch2-6 very much. Perhaps someone can provide interior photos???? IF PCB type, it would need to be replaced by conventional Balun to eliminate the PCB Balun Loss.

Code:
Input file :HiVHF_Stellar-Labs_13El_FD_Yagi_majortom.nec
Freq sweeps: [(54, 1, 35)]
Autosegmentation: NO

         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
   54.0  -2.09 -26.15 1017.36 180.0  -0.05  -0.05    0.85  411.14 1.04  0.17
   55.0  -1.88 -25.69 959.63 180.0  -0.05  -0.05    0.94  423.84 1.04  0.17
   56.0  -1.69 -25.24 904.30 180.0  -0.06  -0.06    1.04  436.98 1.04  0.17
   57.0  -1.51 -24.80 851.41 180.0  -0.08  -0.08    1.15  450.58 1.04  0.17
   58.0  -1.34 -24.37 800.98 180.0  -0.09  -0.09    1.27  464.69 1.04  0.17
   59.0  -1.18 -23.94 753.01 180.0  -0.10  -0.10    1.42  479.33 1.04  0.17
   60.0  -1.03 -23.52 707.47 164.4  -0.11  -0.11    1.58  494.56 1.04  0.17
   61.0  -0.89 -23.11 664.33 151.2  -0.12  -0.12    1.76  510.40 1.04  0.17
   62.0  -0.75 -22.69 623.52 142.7  -0.13  -0.13    1.97  526.90 1.04  0.17
   63.0  -0.63 -22.30 585.00 136.9  -0.15  -0.15    2.20  544.13 1.04  0.17
   64.0  -0.52 -21.91 548.67 132.3  -0.17  -0.17    2.47  562.13 1.04  0.17
   65.0  -0.37 -21.48 514.47 128.3  -0.19  -0.19    2.77  580.98 1.03  0.13
   66.0  -0.27 -21.10 482.30 125.0  -0.21  -0.21    3.12  600.74 1.03  0.13
   67.0  -0.17 -20.72 452.08 121.8  -0.22  -0.22    3.51  621.49 1.03  0.13
   68.0  -0.09 -20.36 423.72 119.5  -0.25  -0.25    3.96  643.32 1.03  0.13
   69.0   0.00 -19.99 397.12 117.2  -0.26  -0.26    4.48  666.32 1.03  0.13
   70.0   0.07 -19.64 372.18 115.2  -0.30  -0.30    5.08  690.62 1.03  0.13
   71.0   0.14 -19.29 348.83 113.4  -0.32  -0.32    5.76  716.34 1.03  0.13
   72.0   0.21 -18.94 326.98 111.7  -0.35  -0.35    6.55  743.61 1.03  0.13
   73.0   0.27 -18.60 306.53 110.2  -0.38  -0.38    7.47  772.61 1.03  0.13
   74.0   0.32 -18.27 287.40 109.0  -0.41  -0.41    8.53  803.52 1.03  0.13
   75.0   0.38 -17.93 269.51 107.5  -0.44  -0.44    9.77  836.54 1.03  0.13
   76.0   0.42 -17.62 252.80 106.5  -0.48  -0.48   11.21  871.94 1.03  0.13
   77.0   0.51 -17.26 237.17 105.4  -0.51  -0.51   12.90  909.98 1.02  0.09
   78.0   0.55 -16.95 222.58 104.4  -0.55  -0.55   14.90  951.01 1.02  0.09
   79.0   0.58 -16.65 208.94 103.6  -0.60  -0.60   17.25  995.41 1.02  0.09
   80.0   0.61 -16.35 196.20 102.8  -0.64  -0.64   20.04 1043.65 1.02  0.09
   81.0   0.64 -16.05 184.30 101.9  -0.69  -0.69   23.37 1096.27 1.02  0.09
   82.0   0.66 -15.76 173.19 101.3  -0.74  -0.74   27.37 1153.93 1.02  0.09
   83.0   0.69 -15.46 162.81 100.5  -0.78  -0.78   32.21 1217.42 1.02  0.09
   84.0   0.70 -15.19 153.11 100.0  -0.84  -0.84   38.09 1287.71 1.02  0.09
   85.0   0.72 -14.91 144.05  99.3  -0.89  -0.89   45.31 1365.99 1.02  0.09
   86.0   0.73 -14.64 135.58  98.8  -0.95  -0.95   54.24 1453.75 1.02  0.09
   87.0   0.73 -14.38 127.68  98.3  -1.02  -1.02   65.41 1552.88 1.02  0.09
   88.0   0.74 -14.12 120.29  97.7  -1.08  -1.08   79.55 1665.76 1.02  0.09
 

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It is most definitely a PCB Balun...
It is L/2 loop 4:1 balun
https://1.bp.blogspot.com/-Ua-2pPb2m58/Ws97jcEsQwI/AAAAAAAAJ8Q/T444-aWqaMQw8RLf5J1Ss3ySfRhDkQKQwCLcBGAs/s1600/4_to_1_balun.png

Folded dipole has 300 Ohm differential impedance (between terminals) or +-150 Ohm odd impedance (between any terminal and ground/null point)

After 150 Ohm impedance of one arm passed L/2 line, it shifts phase by 180 degree.
Then both +150 and rotated -150 Ohm (become +150) come to Tee-joint and combine 2x150 = 75 Ohm

In TX mode, 75 Ohm signal come from cable. In Tee-joint it splits into half power, but same voltage (potential is the same since wires are soldered directly).
When wave energy splits in 2 halves, but amplitude (voltage, E-field density) is the same, it means that wave impedance of resulting 2 waves is doubled (magnetic flux is 2x lower, E field is the same - hence impedance is 150 Ohm).
One half is rotated 180 degree (+1V become -1V).
So when we applied +1V @ 75 Ohm, at output terminals we have +1V @ 150 Ohm and -1V @ 150 Ohm.
Differential voltage at output terminals beceom 2V, differential impedance 300 Ohm.
So it acts as 1:4 step-up transformer. As high-voltage side is differential (balanced) and low-voltage side is assymetrical (unbalanced) this is BalUn 4:1 by definition

This type of balun has 1 drawback: it is relatively narrowband. L/2 line shifts phase 180 degree only at 1 given frequency.
If you produce 180 degree lag at 195 MHz, it is 160 of 200 degree at 174/216 MHz

For optimal wideband matching, L/2 line impedance should be 150 Ohm. Otherwise it will transform impedance (and hence voltage)
 
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