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home-brew vswr meter

Discussion in 'Electronic Basics' started by tom, Mar 18, 2005.

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  1. tom

    tom Guest

    How minimal of circuit would be required to tell the difference between
    whether a load was inductively reactive or capacitively reactive at
    frequencies between 100mhz and 200mhz, and in the 5 to 100 watts range? A
    home made VSWR meter, for someone who doesn't have access to a store-bought
    one, basically.
  2. Active8

    Active8 Guest

    A VSWR meter won't tell you that, just that there's a mismatch.
    Start longer and prune for best VSWR. That's as simple as a couple
    of diodes, a meter, and some resistors and/or a pot - maybe a power
    range switch in leiu of the pot and a switch for forwared/reflected
    power. Additionally you'd need some type of directional coupler - 2
    parallel PCB traces... or a piece of insulated 24 AWG wire threaded
    under a length of coax braid... or a torroidal coil with the coax
    running through it. Unless you can get a crossed-needle display,
    you'll have to calculate the VSWR from the fwd/rev readings or just
    prune until the reflection are minimum. Knowing the VSWR would help
    you compare with other antennas.

    Oh, yeah. Is google's server down or something?
  3. Fred Abse

    Fred Abse Guest

    If, by "VSWR meter", you mean the usual directionally sampled line
    arrangement, it won't tell you. What it actually measures is forward and
    reflected *current*, hence power. Whether the mismatched load is
    resistive, capacitive, or inductive, it neither knows nor cares.

    Google for "VHF bridge", and see if that gives you any ideas
  4. tom

    tom Guest

    I'm not sure I understand your point Mike --- what do you mean by, "Oh,
    yeah. Is google's server down or something?"
  5. dB

    dB Guest

    A directional power meter (s.w.r. meter) will not differentiate
    between the two cases.
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