555 mixer

Discussion in 'The Projects Forum' started by garry.owens, Dec 20, 2008.

  1. garry.owens

    Thread Starter Member

    Dec 17, 2008
    17
    0
    i have found an old radio with frequency counter display this is a normal frequency counter but it is minus 455 for the radio if can i use a 555 timer to add the 455 to get a true reding if so has some wone got a simple mixer circuit that i can use for this purpose
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    How old? 555's are lousey time bases for precision measurements, but the base number 555 can be a transistor or more (check the datasheets in the resources forum here at ACC).
     
  3. garry.owens

    Thread Starter Member

    Dec 17, 2008
    17
    0
    by how old im not sure if you meen the radio or the 555 timer i have several ne 555 as for the rad i would say around 10 year it will be for a panel display on a fuction genarator that i am building
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The offset frequency is most times done by the counter.
    You store the offset value in the counter using the preset inputs.
    When you want to subtract 455 kHz, you store - 455 in the counter.
    When you want to add 455, you store 455 in the counter.
    See timing diagram when the events take place (not to scale).

    [​IMG]

    Greetings,
    Bertus
     
  5. garry.owens

    Thread Starter Member

    Dec 17, 2008
    17
    0
    I HAVE BEEN LOOKING AT THE COUNTER BUT SEE NO PRESETS AT ALL THE ONLY CONECTIONS ARE
    + 9 VOLTS
    _9 VOLTS
    GROUND
    SIGNAL
    THIS IS JUST A CHEEP BASIC OLD CARE RADIO CASET THAT IT CAME OUT OF UNLESS THER IS A SOLDER CONECT THAT I GOT TO DO EG SOME LINK THAT IS ON THE BOARD UNDER THE LCD DISPLAY BUT I HOPE THAT I DO NOT HAVE TO REMOVE THOSE SCREWS AS THEY ARE EXTREMLY DIVICULT TO REDO AND KEEP THE DISPLAY WORKING HAS ANYBODY ATTEMPTED THIS BEFORE AND FOUND A WAY AROUND THIS
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    It would be nice to have some more information on the counter.
    With some counters there are preprogrammed offsets that can be set with jumpers.
    These jumpers sometimes look like a pair of copper lands with a line in between.
    These lands can be connected useing a bulb of solder.

    Greetings,
    Bertus
     
  7. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287

    Hi Gary:

    Here is a real slick trick.....it's top secret so don't tell anyone......sHHHHHH!

    Take your existing local oscillator, and re-mix it back with a sample of your I.F. Take the the difference frequency. This will be PRECISELY the incoming R.F. frequency.....any error in your local oscillator frequency will be cancelled!

    Eric

    p.s. yeah...I know it requires a few more components, but this gives you an accurate way of measuring your incoming frequency.
     
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