CRO DISPLAY on Microwave Testbench

Discussion in 'Wireless & RF Design' started by vinodquilon, Jun 9, 2011.

  1. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    234
    0
    In the Microwave Testbench shown,
    I am replacing VSWR Meter with another CRO.
    Then, What would be the waveforms on two CROs ?

    According to my prediction:
    CRO at Detector Mount will indicate SQUARE WAVES( AM modulation set on MW source supply)
    CRO at slotted line will indicate STANDING SINE WAVES tracked by the slotted line

    Is it correct ?




    [​IMG]
     
    Last edited by a moderator: Jun 9, 2011
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    A VSWR is a standing wave meter.
    This will show the standing wave of the current choosen frequency.
    A CRO can be used as a signal indicator, but can not show the VSWR without any help of other parts.

    BTW what are you trying to do with the microwave bridges?
    This is already the second thread about them.

    In my job I have to deal with EPR systems.
    Those use microwave bridges to measure electron spin signals.
    http://www.bruker-biospin.com/cw.html
    http://www.bruker-biospin.com/cwpractice.html

    Bertus
     
    Last edited: Jun 9, 2011
  3. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    234
    0

    Hi Bertus,

    I don't want to measure VSWR through CRO, but wanna know
    what will be the display on CRO at slotted end.

    There is an option for choosing between SQUARE WAVE AM & SWEEP WAVE FM MODULATION in Microwave power supply.
    I have set it on AM.
    Then modulated signals will be in SQUARE shape.What would be the shape of STANDING WAVES ?
    Can I display these Standing Waves on CRO connected at Slotted end ?

    Can I connect VSWR meter at the end of Detector Mount XD-451 to measure VSWR reading ?
     
    Last edited: Jun 9, 2011
  4. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    234
    0
    I got the idea.

    I am not displaying standing waves on an oscilloscope, a standing wave

    is not a time-varying voltage.

    The standing wave is a voltage which varies with the position along

    the line.


    One more doubt----- for 'peak' points of standing waves, SWR needle

    moves to 'low' positive db gain values(towards right-max.needle

    deflection). Similarly, for trough points of standing waves ,SWR

    needle moves to peak positive db values(towards left).

    Why this contradiction exists ?
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    I believe it is due to the fact that standing waves are reflections. A peak in a standing wave represents a point where the reflected power partially cancels out the transmitted power.
     
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