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DC blocking cap value type suggestion

Discussion in 'Radio and Communications' started by Artem N., Feb 12, 2016.

  1. Artem N.

    Artem N. New Member

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    Hi, I'm building a diversity transiever based on hopeRF rfm22b module and a
    SKY13267-321 diversity antenna switch. The switch needs dc blocking caps on all rf inputs/outputs. I need help in choosing the correct value/package capacitor for 433MHz band. More precisely should i be matching 50ohm or trying to achieve close to 0 ohm impedance? Also I've seen a few examples of amp coupling circuits which all fell in the 1.78-1.82ohm range.
    Thank you!
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Normally a dc block capacitor is made large enough so it has an impedance much smaller than the input and output impedances.
    Surface mount types, the smaller physical size the better, have the lowest lead inductance and are usually preferred for RF.
     
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Their eval board comes with these DC blocking caps:
    upload_2016-2-13_14-51-21.png
    presumably for the useful range (LF-6GHz). Although, 433MHz is at the very low end.
     
  4. dave

    Dave New Member

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  5. Artem N.

    Artem N. New Member

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    Yep, I've seen the dev kit default caps, however it is more for 2.4/5.8ghz band, at 433mhz those caps produce 78ohms of Xc...

    So I'll match up the smallest form factor with the lowest impedance...

    Thank you Crut!
     
  6. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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