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Ceramic filter pinout and help with a 455khz BFO

Discussion in 'General Electronics Discussion' started by Richard9025, Jul 1, 2017.

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  1. Richard9025


    May 24, 2016
    Hi !
    I salvaged a 455khz ceramic filter from a CB radio , but I cant find any datasheets or relevant info on the internet
    Some photos :

    WhatsApp Image 2017-07-01 at 9.24.27 PM.jpeg

    WhatsApp Image 2017-07-01 at 9.24.27 PM(1).jpeg

    WhatsApp Image 2017-07-01 at 9.24.27 PM(1) - Copy.jpeg

    If you can't determine which pin is which , I can take some photos of the radio that it was extracted from (eurocb micro 2) , maybe a schematic and the photos will get the answer .
    Now with the BFO (it is based on the model from IK1ZYW
    In the following schematic I assumed that pin 1 is output , pin 2 ground and pin 3 input :

    455KHZ BFO no outp - Copy.jpg

    The votage regulator works , from an input of 9V i get 5.1V
    Now , to test if it works , I connected it to an SDR , but I can't see the oscillation on 455khz :
    With it connected , I dont see anything , no change
    But if I rotate R2 (a multiturn , 10 turns , pot) or I just get near the bfo , look at what happens , if I get away , it dissapears :


    Yeaa , messy stuff

    Thanks !
    Last edited by a moderator: Jul 1, 2017
  2. davenn

    davenn Moderator

    Sep 5, 2009
    always dangerous to assume

    confirm it from the radio you took the filter out of
    Richard9025 likes this.
  3. Richard9025


    May 24, 2016
    I forgot to connect C3 to ground , now it works perfectly , thanks !
    davenn likes this.
  4. davenn

    davenn Moderator

    Sep 5, 2009
    good to hear :)
    Richard9025 likes this.
  5. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Richard9025

    There would be two uses for a BFO . . . one would be for the use of the reception of upper and lower SSB VOICE communications .

    The other would be for the reception of code signals .... . .-.. .-.. --- --- ---.

    If the former, can you tolerate the audio rate modulating square wave frequency that the '14 is generating in order to "BANG" the ceramic filter into shocked state operation, in order to generate its 455khz signal.

    As for using it on the latter situation of receiving a code signal, that might be permissible, if it doesn't heterodyne with the converted audio signal.

    Most people typically will use an already on hand or easily locatable 455 khz IF transformer in a conventional oscillator circuit to get their pure sine BFO signal..


    If that is your signal above . . . . . that situation is now being different, as you are banging the unit with a 22.8 khz driving signal, which would be up on in the ultrasonic range.
    No problems.

    73's de Edd
    Last edited: Jul 2, 2017
    Richard9025 likes this.
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