Multi-Band Dipoles G5RV vs ZS6BKW G5RV Louis Varney -- G5RV (SK) - - PowerPoint PPT Presentation

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Multi-Band Dipoles G5RV vs ZS6BKW G5RV Louis Varney -- G5RV (SK) - - PowerPoint PPT Presentation

Feb 28, 2023 174 likes •423 views

Multi-Band Dipoles G5RV vs ZS6BKW G5RV Louis Varney -- G5RV (SK) 1934 102 ft 3/2 WL 20 M dipole 72 Ohm twinlead to shack 300 Ohm matching section for 40 M 30 ft is WL for 20 M & WL for 40 M What about other

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SLIDE 1

Multi-Band Dipoles

G5RV vs ZS6BKW

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SLIDE 2

G5RV

  • Louis Varney -- G5RV (SK)
  • 1934
  • 102 ft 3/2 WL 20 M dipole
  • 72 Ohm twinlead to shack
  • 300 Ohm matching section for 40 M
  • 30 ft is ½ WL for 20 M & ¼ WL for 40 M
  • What about other bands?
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SLIDE 3

3/2 WL 20M Dipole

  • Three 20 M halfwave dipoles
  • Tied end-to-end
  • About 33 to 34 feet each
  • Total about 100 feet … or so
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SLIDE 4

EZNEC

  • Calculate antenna impedances
  • Calculate antenna gain
  • Calculate far field plot
  • Calculate antenna current
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SLIDE 5

3/2 WL 20M Dipole

  • Three 20 M halfwave dipoles
  • Tied end-to-end
  • About 33 feet each
  • Total about 99 feet … or so
  • Three current nodes – Nodes are peaks
  • When current is high, voltage is low
  • R = E/I … Therefore impedance is low
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SLIDE 6

3/2 WL 20M Dipole at 40M

  • Halfwave at 20 M is quarterwave at 40 M
  • 3/2 WL 20M is ¾ wavelength at 40 M
  • Check EZNEC
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SLIDE 7

G5RV

  • Louis Varney -- G5RV (SK)
  • 1934
  • 102 ft 3/2 WL 20 M dipole
  • 72 Ohm twinlead to shack
  • 300 Ohm matching section for 40 M
  • 30 ft is ½ WL for 20 M & ¼ WL for 40 M
  • What about other bands?
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SLIDE 8

Matching Section

  • ¼ WL transmission line makes high Z to low Z
  • ½ WL transmission line preserves Z
  • ¾ WL transmission line makes high Z to low Z
  • 1 WL transmission line preserves Z
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SLIDE 9

“Bullseye” SWR Chart

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SLIDE 10

Use SimSmith for Bullseye

  • Use 3:1 SWR target

– Radio likes 1:1 – Radio limits above 3:1 – All auto tuners will match 3:1 – Limited coax loss at 3:1 and below

  • Use antenna Z file from EZNEC
  • Use simple transmission line
  • Set generator Z to 75 Ohms
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SLIDE 11

Matching Section

  • ¼ WL transmission line makes high Z to low Z
  • ½ WL transmission line preserves Z
  • ¾ WL transmission line makes high Z to low Z
  • 1 WL transmission line preserves Z
  • G5RV designed for 20 & 40 M
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SLIDE 12

3/2 WL 20M Dipole at 40M

  • Halfwave at 20 M is quarterwave at 40 M
  • 3/2 WL 20M is ¾ wavelength at 40 M
  • Look at EZNEC
  • Current nodes of ¾ WL are displaced from center
  • The center is almost a current minimum
  • Center voltage is therefore high
  • Center impedance is high
  • ¼ WL transmission line will transform Z to low
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SLIDE 13

Matching Section

  • ¼ WL transmission line makes high Z to low Z
  • ½ WL transmission line preserves Z
  • ¾ WL transmission line makes high Z to low Z
  • 1 WL transmission line preserves Z
  • Look at Bullseye
  • G5RV designed for 20 & 40 M
  • Is 5/2 WL at 12 M and TL is 1 WL so OK
  • Would be OK at 16 M but not ham band
  • No other bands?
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SLIDE 14

ZS6BKW

  • Brian Austin -- ZS6BKW 1980 (or so)
  • “Computer optimized” G5RV
  • 92 ft dipole
  • 50 Ohm feed to shack
  • 39-40 ft 400 Ohm downlead
  • 40, 20, 17, 12, 10 M match?
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SLIDE 15

W5DXP resource

  • Cecil Moore – W5DXP
  • Likes matching with balanced window line
  • Has 130 ft dipole and method for matching
  • Plots antenna length with matching section
  • Investigated ZS6BKW
  • Has many ideas for additional band match
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SLIDE 16

ZS6BKW

  • Brian Austin -- ZS6BKW 1980 (or so)
  • “Computer optimized” G5RV
  • 92 ft dipole
  • 50 Ohm feed to shack
  • 39-40 ft 400 Ohm downlead
  • 40, 20, 17, 12, 10 M match?
  • Check W5DXP
  • Look at EZNEC & check Bullseye
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SLIDE 17

G0GSF

  • G0GSF 2018 (February RadCom)
  • 96 ft inverted U
  • “Shorter” than 40 M dipole – 46 ft top
  • 25 ft ends hang straight down
  • 50 Ohm feed to shack
  • 40 ft 400 Ohm matching section
  • Match like ZS6BKW
  • Brian Austin -- G0GSF
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G0GSF

  • Check W5DXP
  • Check EZNEC
  • Check Bullseye for matches
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SLIDE 19

G0GSF

  • G0GSF 2018 (February RadCom)
  • 96 ft inverted U
  • “Shorter” than 40 M dipole – 46 ft top
  • 25 ft ends hang straight down
  • 50 Ohm feed to shack
  • 40 ft 400 Ohm matching section
  • Match like ZS6BKW
  • Brian Austin G0GSF was ZS6BKW!
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SLIDE 20

Links

  • KC7HXC: Google -> coax loss antenna gain
  • http://www.ae6ty.com/Smith_Charts.html
  • http://www.w5dxp.com/
  • http://www.w5ddl.org/files/Zs6bkw_vs_G5rv_2010022

1b.pdf

  • http://ars.nc4fb.org/zs6bkw/zs6bkw-antenna-from-

the-horses-mouth-by-g0gsf.pdf

  • http://www.nc4fb.org/wordpress/zs6bkw-multi-band-

antenna/

  • http://www.wirelesswaffle.com/index.php?m=02&y=0

7&entry=entry070209-160601

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Links

  • KC7HXC: Google -> coax loss antenna gain
  • http://www.ae6ty.com/Smith_Charts.html
  • http://www.w5dxp.com/
  • http://www.w5ddl.org/files/Zs6bkw_vs_G5rv_2010022

1b.pdf

  • http://ars.nc4fb.org/zs6bkw/zs6bkw-antenna-from-

the-horses-mouth-by-g0gsf.pdf

  • http://www.nc4fb.org/wordpress/zs6bkw-multi-band-

antenna/

  • http://www.wirelesswaffle.com/index.php?m=02&y=0

7&entry=entry070209-160601

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