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RF relay ground connections

Discussion in 'Electronic Design' started by Joel Koltner, Mar 12, 2008.

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  1. Joel Koltner

    Joel Koltner Guest

    Has anyone here used the type of RF relay that's packaged like this one:
    http://www.rfrelaystore.com/productdesc.php?pid=RDT-2P1D6 ? If you look at
    the mounting drawing link on that page
    (http://www.rfrelaystore.com/pdf/mounting/1500901.PDF), the idea is that your
    hog out a pocket on your PCB for the relay to sit in and your microstrip
    traces contact the relay terminals clearnly. However, shouldn't I be worried
    that there isn't really a ground connector between the relay and the PCB's
    ground plane that I can see? At 6GHz you're looking at wavelengths on the
    order of an inch on a PCB, and the relay is a significant fraction of that so
    it seems as though keeping proper ground references around would be necessary.
    Perhaps the coupling between the bottom side of the relay and your ground
    plane (a good-sized capacitor) is enough to make everything kopesetic?
    Running a few numbers on the back of an envelope gives me somewhere in the
    ballpark of upwards of 10pF (depends on where the ground plane actualyl is,
    obviously) which is -j16 ohms at 1GHz -- not entirely ignoranble.

    ---Joel
     
  2. John Larkin

    John Larkin Guest

    It looks like they want you to hog out a square-cornered pocket in the
    pcb and then tap the board as well! I suppose you could sit it on a
    ground plane, on the bottom of the pocket.

    I have done plated countersinked holes on a pcb, but never tapped
    holes!

    John
     
  3. Mark

    Mark Guest

    the bottom surface in the drawing is the HOUSING not the PWB. The PWB
    sits on top of the metal housing, the relay is screwd to the housing
    and the PWB ground must also be well connected to the housing for this
    to work

    Mark
     
  4. Joel Koltner

    Joel Koltner Guest

    Hi Mark,

    "the bottom surface in the drawing is the HOUSING not the PWB. The PWB
    sits on top of the metal housing, the relay is screwd to the housing
    and the PWB ground must also be well connected to the housing for this
    to work"

    Ah, gotcha. Thanks for the explanation...

    Hmm... I wonder if it's easier (cheaper) to get your board house to build up a
    ..049" thick board than it is to hog out the housing to the appropriate
    remianing depth?

    ---Joel
     
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