+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Junior Member level 3
    Points: 545, Level: 4

    Join Date
    Dec 2014
    Posts
    27
    Helped
    0 / 0
    Points
    545
    Level
    4

    capacitor selection for antenna tuning

    Hello Guys,

    In antenna tuning for EM Prox (LF) can we use X7R capacitors??? They recommend NP0 capacitor only for antenna tuning... If I use X7R what will happen???

    •   AltAdvertisment

        
       

  2. #2
    Advanced Member level 5
    Points: 20,157, Level: 34
    Achievements:
    7 years registered

    Join Date
    Jan 2011
    Posts
    3,322
    Helped
    1181 / 1181
    Points
    20,157
    Level
    34

    Re: capacitor selection for antenna tuning

    X7R is a class II dielectric while NP0 is a class I dielectric. Class I will tend to have higher stability in terms of voltage/temperature, and generally lower losses. Also class I dielectrics tend to have less piezoelectric effects. But these classifications are quite broad and if you really want to be sure then you should look at specific devices and their datasheets.



    •   AltAdvertisment

        
       

  3. #3
    Super Moderator
    Points: 251,556, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    43,806
    Helped
    13321 / 13321
    Points
    251,556
    Level
    100

    Re: capacitor selection for antenna tuning

    Intended coupler bandwidth and respective frequency stability requirements will answer the question. I won't use X7R for any kind of resonant circuit.



    •   AltAdvertisment

        
       

  4. #4
    Advanced Member level 5
    Points: 33,445, Level: 44

    Join Date
    Oct 2001
    Posts
    4,784
    Helped
    1413 / 1413
    Points
    33,445
    Level
    44

    Re: capacitor selection for antenna tuning

    Yes, for high frequencies (>30MHz) X7R capacitors are not recommended for resonators, but for lower frequencies they should be fine.

    http://www.avx.com/docs/catalogs/cx7r.pdf



  5. #5
    Advanced Member level 5
    Points: 34,760, Level: 45
    Achievements:
    7 years registered Created Blog entry Created Album pictures
    SunnySkyguy's Avatar
    Join Date
    Sep 2007
    Location
    Richmond Hill, ON, Canada
    Posts
    6,698
    Helped
    1671 / 1671
    Points
    34,760
    Level
    45
    Blog Entries
    7

    Re: capacitor selection for antenna tuning

    What frequency?

    The term "proximity card" refers to the older 125 kHz devices as distinct to the newer 13.56 MHz contactless smartcards.

    You can also use diodes used as a varicap for fine tuning which increase in pF size with power rating but wide tolerance for any diode.
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



    •   AltAdvertisment

        
       

  6. #6
    Newbie level 3
    Points: 60, Level: 1

    Join Date
    Apr 2015
    Posts
    4
    Helped
    0 / 0
    Points
    60
    Level
    1

    Re: capacitor selection for antenna tuning

    Quote Originally Posted by FvM View Post
    Intended coupler bandwidth and respective frequency stability requirements will answer the question. I won't use X7R for any kind of resonant circuit.
    Definitely! X7R normally used for digital and power area not RF/antenna field.



--[[ ]]--