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How does a forward and reverse power meter work?

  1. May 1, 2015 #1
    I know they have a diode that gets reversed to see forward V reverse power but how does that diode just respond to the one direction of energy? I have a bird wattmeter and it uses two slugs, one pointed in the other out to get simultaneous forward and reverse power and VSWR and such but why does reversing the diode change the response from forward to reverse? I have a hard time visualizing the process. Thanks. AI3N (All In 3 Nights)
  2. jcsd
  3. May 1, 2015 #2


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    hi there

    this schematic of a Bird Wattmeter may help you


    all the labelled parts in the middle are within the slug
    Note the sensing loop parallel to the coaxial line and the diode. The induced current into the loop is rectified by the diode.
    When it is orientated one way .. .say as shown it will "see" current induced that is flowing on one direction in the coaxial line.
    Rotate the slug and it will "see" and rectify induced current flowing the opposite direction in the coax line

    ( not the best wording, but hopefully you will get the idea :smile: )

  4. May 2, 2015 #3


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    A small proportion of the energy propagating along the transmission line is directionally coupled into the coupling loop. One way to think of it is that depending on the direction of the coupled energy, it will either be absorbed in the termination resistor or detected at the opposite end of the loop by the diode.
    You should be aware that tricky things often happen in couplers. Depending on the mode employed, the energy in the coupling loop may appear to be coupled in the opposite direction to the transmission line.

  5. May 2, 2015 #4


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    Truer words were never spoken!
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