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Transmitter troubles

Discussion in 'General Electronics Discussion' started by housecat, Apr 6, 2012.

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  1. housecat

    housecat

    1
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    Apr 6, 2012
    Trying to build this: http://www.talkingelectronics.com/projects/CrystalLockedBug/CrystalLockedBug-1.html

    Alterations: slightly smaller pcb, mostly SMD caps and resistors, no audio stage yet (replaced by an old mp3 player), pn2222's instead of bc-whatevers, air core coils, resistor instead of inductor in buffer stage.

    I've built several of these, and the only one I got to work somewhat properly was a 72Mhz NBFM version (24mhz crystal, first oscillator stage 24mhz as well, the second 72). Also tried to build several WBFM versions like in the original schematic (11/33/66, 11/33/99, 11/55/110, 14.318/42.954/85.908 etc etc etc), but none of these could be adjusted to its proper frequency. NO modulation whatsoever on center frequency, poor signals with modulation 1-2 mhz off to either sides... and the "side" frequencies drift, in fact you could (temporarily) adjust these in at least 10mhz range, it seems as if the crystal isn't really doing anything at all in there... Very little audio power is required for this WB modulation (2 on scale of 30 on the audio player, the NB variety needs about 25). Cranking the volume up won't produce audio on center frequency, the signal just becomes intermittent... Any help appreciated..
     
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