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phase shifter circuit needed

Discussion in 'Electronic Repair' started by Patrick, Jul 4, 2005.

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  1. Patrick

    Patrick Guest

    I'm looking to build to a phase shifter circuit that can supply about 60
    degrees of phase shift at 70 MHz (bandwidth not important). The phase shift
    needs to be adjustable in real time, ie, with a variable R or C.

    The catch is that the input and output of the network needs to remain
    matched to 50 ohms.

    Can this even be done with purely passive components?

    (Specifically, what I have is a transmission line that needs to provide a
    180-degree shift from the start of the line to the end. The problem is we
    have no way to precisely measure the length of the TL. So we need a way to
    adjust the "length" of the line in real time. Now, I'm aware of the
    trombone method, wherein a piece of TL is slid in and out to provide a
    variable lenght. However, this is a mechanical solution and not suited for
    the application; ergo I need a way simulate this behaviour)

    Thanks very kindly
     
  2. Asimov

    Asimov Guest

    "Patrick" bravely wrote to "All" (03 Jul 05 22:32:10)
    --- on the heady topic of "phase shifter circuit needed"

    Pa> From: "Patrick" <>
    Pa> Xref: aeinews sci.electronics.repair:52356

    Pa> I'm looking to build to a phase shifter circuit that can supply about
    Pa> 60 degrees of phase shift at 70 MHz (bandwidth not important). The
    Pa> phase shift needs to be adjustable in real time, ie, with a variable R
    Pa> or C.
    Pa> The catch is that the input and output of the network needs to remain
    Pa> matched to 50 ohms.

    Pa> Can this even be done with purely passive components?

    Pa> (Specifically, what I have is a transmission line that needs to
    Pa> provide a 180-degree shift from the start of the line to the end. The
    Pa> problem is we have no way to precisely measure the length of the TL.
    Pa> So we need a way to adjust the "length" of the line in real time. Now,
    Pa> I'm aware of the trombone method, wherein a piece of TL is slid in and
    Pa> out to provide a variable lenght. However, this is a mechanical
    Pa> solution and not suited for the application; ergo I need a way simulate
    Pa> this behaviour)
    Pa> Thanks very kindly


    Try looking into active all-pass filter networks. This requires a few
    transistors though.

    A*s*i*m*o*v

    .... Transistor: The sister that used to be your brother.
     
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