absorptive swr bridge

Discussion in 'The Projects Forum' started by ninjaman, Sep 25, 2014.

  1. ninjaman

    Thread Starter Member

    May 18, 2013
    I want to make an antenna analyser using arduino. I have seen diy antenna analysers and their swr meters for getting voltages and finding impedances but im not sure I understand them that well.
    I have read about wheat stone bridges and understand that I need a 50 ohm resistors as a way of comparison. I know that the ratio on both legs must be equal meaning R1/R2 = R3/Rx, (x being the unknown impedance)
    I have looked at some previous models that are available that use 8 bit microcontrollers. not arduinos but there arduino is an 8 bit that has a 10 bit ADC. not the same as the others which I think have 12 bit ADC.
    the other projects use a reflectometer, absorptive swr bridge with diode detectors and compensated buffer amplifiers.
    now the absorptive swr bridge I kind of understand. its a wheat stone bridge with 50 ohm power resistors, that absorbs power so you will most likely always see a low impedance which is supposed to limit possible damage to the transmitter. (that is what I understood of it?). I don't know about the "compensated op amps", or diode detectors. I know what a diode detector is in that it detects the envelope of the signal and blocks any signal in the opposite direction. giving half wave instead of full wave. on the schematics of other projects these diodes go into a capacitor which I imagine help to provide a stable output?
    im not sure about the op amps function and I have never heard of a compensated op amp. this I will research.
    for now I wanted to know if there was an easier way to measure impedance?
    the absorptive bridge requires four voltages, a forward, reverse, voltage at the antenna and voltage across a known resistor in the bridge.
    I think I will try to make a wheat stone bridge using 51 ohm 2 watt resistors and see what I can do there.
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    search for "return loss bridge" thats what your looking for.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
  4. DickCappels


    Aug 21, 2008