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ON7YK - (ex)ON1ABO - (ex)ON7CB
C5YK - C5S - (ex)C56YK

On the web since 2001
Belgian / Gambian Radioamateur Station

The Quarter Wave stub .


Purpose : To attenuate the harmonics on the higher or lower bands, with or without a shorted or open stub .

Protect you multi station Rx input : Low power protection with a stub .
Band Stubs
160 Meter λ/4 Shorted stub to kill harmonic on 80 Meter band
80 Meter λ/4 Shorted stub protect 40, 20, 15 and 10 Meter Band
40 Meter λ/4 Shorted stub protect 20 Meter and 10 Meter band
λ/2 Open stub kills harmonic from 80 Meter band
λ/6 Shorted stub + λ/12 Open stub kills 15M harmonic
20Meter λ/4 wave Shorted stub protects 10 Meter band
λ/2 Open stub protects 15 (3/4 on 15), kills 40 Meter band harmonic
15 Meter 3 x λ/4 wave Shorted stub protects 20 and 10 (1/4 wave on 40 Meter)
10 Meter λ/2 wave Open stub protects RX from 20 Meter
1 λ wave Open stub protects RX from 40M and 15M (λ wave on 40 Meter)
Or using high power Bandpass filter protection for high power output .

Calculator

Frequency (MHz): Enter Value
Velocity factor: Enter Value
Length of Quater wave stub (m): Calculated
Length of Half wave stub (m): Calculated
Wave length in the transmission line (m): Calculated
Wave length in free space (m): Calculated
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My own design for 80m and 20m :

Using RG8 / RG-213 = vf 0,66 .( both coax type are also for high power )
PL259 connectors and T - PL259 connector .
! There is a noticeable difference between the rig expert and the Nanovna for finding the required frequency for the stub .!
( My observation : the Nanovna H4 is much more correct than the rigexpert .)

  • Result : λ/4 wave shorted stub for 20m band Length = 3,53m for 14.020 Mhz .
  • Result : λ/4 wave shorted stub for 80m band Length = 14,05m for 3.523 Mhz .

Measuring with Rigexpert AA-55 zoom :

  • Cut the coax a bit longer than the calulated length .
  • Pusch teh Rig expert on and go to the menu : Tools , next to Menu Stub .
  • Connect the coax to the rigexpert .
  • Pusch ok and you find the reslut for a far end : OPEN .
  • Short the end of the stub .
  • Pusch ok and you find the reslut for a far end : Close .

Measuring with Nanovna H4:

  • SWR on main band is wide and cover the hole band .
  • The harmonic filter on all other bands are small .

Result : λ/4 wave shorted stub for 20m band protects RX on 28Mhz with -26dB .

Result : λ/4 wave shorted stub for 80m band protects RX on 7Mhz , 14Mhz, 21Mhz and 28Mhz from -23dB till -17dB .

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