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Finding antenna on key fob

Discussion in 'General Electronics Discussion' started by starscream, May 28, 2016.

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  1. starscream

    starscream

    17
    1
    Sep 27, 2015
    [​IMG] [​IMG]

    Hi guys. I am playing around with a key fob circuit and i want to put it in a new enclosure with an external SMA antenna.
    I am having trouble finding where to solder my coaxial cable antenna and shield points on the circuit. My guess would be that it is the two gold colored pads on the top right of the second image, just above the tactile switch. The top pad being the antenna point and the one below it being the shield.

    Does this seem like the correct points? Any advice would be appreciated. Thanks.
     
  2. 73's de Edd

    73's de Edd

    3,000
    1,262
    Aug 21, 2015
    Sir starscream . . . . . . .

    This is your 433Mhx RF output path to the antenna helix.

    [​IMG]

    Marginal or Inadequate range ? this would be my absolute last attempt . . . work at the receiver end.



    73's de Edd
     
    Last edited by a moderator: May 28, 2016
  3. KJ6EAD

    KJ6EAD

    1,114
    158
    Aug 13, 2011
    For the receiver, Elsema's highest gain stock antenna is the ANT433M. If that isn't adequate, look for an amplifier or a directional antenna if you can use a directional in your application.
     
  4. starscream

    starscream

    17
    1
    Sep 27, 2015
    Thanks for pointing out the helical antenna. If i were to solder some coaxial to the start of the antenna on the circuit would that work or would most of the power be diverted to the inbuilt helical antenna?
     
  5. 73's de Edd

    73's de Edd

    3,000
    1,262
    Aug 21, 2015
    most of the power would be diverted to the inbuilt helical antenna.
    Tell us what your systems problem is.
     
  6. starscream

    starscream

    17
    1
    Sep 27, 2015
    There's no problem with the system. I just cracked the key fob housing and want to put it in a new enclosure. I want to see if i can extend the range by altering the transmitter itself. This is purely for a fun project as apposed to a key fob that i use daily and that needs repair.
     
  7. starscream

    starscream

    17
    1
    Sep 27, 2015
    Would adding a second antenna reduce the range since power would be diverted between 2 antennas?

    Im new to the RF side of things.
     
  8. davenn

    davenn Moderator

    13,722
    1,913
    Sep 5, 2009
    adding a second antenna will ruin the impedance matching to the first antenna rendering it practically useless
     
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