Help: Mc3372

Discussion in 'Wireless & RF Design' started by hamopp, Apr 25, 2013.

  1. hamopp

    Thread Starter Active Member

    May 13, 2009
    68
    1
    Hi All
    I'am having some probs with a if amp that uses a mc3372 chip.

    There is a crystal osc on pin1 and pin2, i'am trying to read the
    frequency of the oscillator to make sure that it is 10.245Mhz.

    I used a 10x probe on my counter and read 10,24258Mhz on pin 1,
    (base of internal transistor), but on pin 2 (emitter of internal transistor)
    i get 10.695Mhz but it is jumping around, up to 10.815Mhz, it's all over
    the place.
    Anyone got any hints as to what might be wrong ?.

    Regards
    Howard
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    Are you currently using the decoupling capacitors as given in the datasheet schematics?
    There are always a 10 μF and a 0.1 μF accross the powersupply to ground.

    Bertus
     
  3. hamopp

    Thread Starter Active Member

    May 13, 2009
    68
    1
    Hi
    This amp\detector is the one from QRP 2m FM Transceiver PP-002m
    http://www.ariroma.it/docs/projects/pp_002m.pdf

    I have built it from L4 up to and including the audio amp, as you can see
    that there is only a 100nF on the in\output of ic 8 (LM7805) but no 10 μF
    accross the power supply to ground.

    Howard
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    I think that using the probe on the oscillator, will put a load to it.
    The probe capacitance will influence the frequency.

    Bertus
     
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