home-brew vswr meter

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

  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.
     
    tom, Mar 18, 2005
    #1
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  2. tom

    Active8 Guest

    On Fri, 18 Mar 2005 13:54:01 GMT, tom wrote:

    > 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.


    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?
    --
    Best Regards,
    Mike
     
    Active8, Mar 18, 2005
    #2
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  3. tom

    Fred Abse Guest

    On Fri, 18 Mar 2005 13:54:01 +0000, tom wrote:

    >
    >
    > 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.


    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


    --
    "Electricity is of two kinds, positive and negative. The difference
    is, I presume, that one comes a little more expensive, but is more
    durable; the other is a cheaper thing, but the moths get into it."
    (Stephen Leacock)
     
    Fred Abse, Mar 18, 2005
    #3
  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?"
     
    tom, Mar 18, 2005
    #4
  5. tom

    dB Guest

    "tom" <> wrote in message news:<Z3B_d.711235$Xk.444675@pd7tw3no>...
    > 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.


    A directional power meter (s.w.r. meter) will not differentiate
    between the two cases.
     
    dB, Mar 18, 2005
    #5
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