NanoVNA: Measurements

[last updated: 2023-11-13]
nanoVNA home page
ham radio home page
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Measurements:
• "S11" defines a reflection measurement, where you send a signal out a port, then measure its reflection back to the same port.
  Ch-0 is a S11 measurement.
• "S21" defines a "through" measurement; inserting a signal out one port, through your device, and receiving and measuring it at the other port.
  Ch-1 is a S21 measurement.
• Measure inductance with far end open (???)
• Measure capacitance with far end shorted (???)

• CALIBRATE the nanoVNA before taking any measurement.
  If doing a "through" measurement, be sure to calibrate "ISOLATION" and "THROUGH" parameters.
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• Measure SWR of antenna:
  • Connect antenna to CH0
  • Turn off the extra traces to make the screen less cluttered (see Operation Notes above).
  • The default for trace 0 is LOGMAG on CH0. But if the trace (color) you want to use is instead set to CH1, change it to CH0 with:
        menu > DISPLAY > CHANNEL > CH0 REFLECT
    Then set it to read SWR with:
        menu > DISPLAY > FORMAT > SWR

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• Measure Impedance of antenna:
  ... Still do not have this dialed in, but here's the resources I'm studying ...
  • forum post with links: https://nanorfe.com/forum/how-to-measure-antenna-impeadance-with-the-nan...
  • good broad view, worthless for details:
  • interesting, good for tuning, nothing about actual impedance value: https://www.youtube.com/watch?app=desktop&v=xa6dqx9udcg
  • too much clutter and verbage to even finish: https://www.youtube.com/watch?v=5I6WQFdSHkQ&t=8s
  • same guy, couldn't watch to the end: https://www.youtube.com/watch?v=2I5e3j7R7ho
  • too much verbage: https://www.youtube.com/watch?v=YTzGjLOV1mk
  • great set of videos on all things ham electronics... : https://www.youtube.com/@w2aew/videos
  • good, well-done, a little complicated: https://www.antenna-theory.com/measurements/impedance.php

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• Measure impedance:
  • From: (link to:) youTube
    • Z_o = reference impedance (usu. 50 ohms)
      Z_d = impedance of Device Being tested
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      Three methods:

    • Shunt connection:
      Use this method to measure impedances near Z_o.
      connect component/module to be measured between nano CH0 and ground
      measure s11 - reflection coefficient (rho)
      s11 = (Z_d - Z_o) / (Z_d + Z_o)
      Z_d = Z_o * (1 + s11) / (1 - s11)
      from forum somewhere...
      Smith Chart horizontal axis is the real part of the reflection coefficient from -1 to +1, with zero being in the centre.
      The vertical axis is the imaginary part of the reflection coefficient, again from -1 to +1.

      
      RL (return loss)=20*log(rho)

      
      Guessing from here ...
      for a vertical antenna: connect coax feedline to Ch-0
      ("far end" will of course be open...)
      Set MENU --> DISPLAY --> FORMAT --> MORE --> RESISTANCE

    • Series Through connection:
      Use this method to measure impedances much greater than Z_o
      connect component between CH0 and CH1
      measure through gain and phase, s21

    • Shunt Through connection:
      Use this method to measure impedances much less than Z_o
      connect signal pin from CH0 to Ch1
      connect component between that and ground
      measure s21

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• Measure Filters and Chokes:
  ... uses "S21" ie. "through" measurement configuration...
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• Measure Inductance:
  • One method - resonant frequency:
    using NanoSaver PC software
    (from: https://www.youtube.com/watch?v=3LOEhvFII6c)
    • connect unknown inductor in series with a known capacitor
      this creates a L-C series-resonant circuit
      connect this circuit across signal and ground of port-0
    • set up nanoVNA with nanoSaver to operate/display using a PC.
      select S-11 phase mode
      plot will show freq when it crosses over x-axis
      this is the resonant freq of the L-C series circuit you have.
    • calculate inductance from:
      f_MHz = f(L_H, C_F)
            = 1 / (2pi (LC)^1/2)
      L = 1 / (4 C f² pi²)
  • Another method - Shunt...
    Generally considered accurate between 20 &200 ohm impedances
    • Connect unknown inductor across signal and ground of CH-0
    • ... not sure which display/measurement option to use...
      but inductance will be read directly at top of screen
    • adj nano cursor to read that point (frequency) where the impedance of load = ~ 50ohm impedance of transmission line
  • another method?

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• Measure Capacitance:
  • connect unknown capacitor across signal/ground of Ch-0
  • set up nanoVNA to read Smith chart:
    MENU --> DISPLAY --> FORMAT --> SMITH
  • rotate thumb wheel to select lowest frequency on the display
  • read capacitance on smith chart measurement line at top of the screen

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  https://www.youtube.com/watch?v=MBGyGRb_7Tg
  measure return loss of a coax, using logmag (at 12:10)

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