Wondering if Possible?

Discussion in 'Wireless & RF Design' started by n0rseman, Jul 19, 2012.

  1. n0rseman

    Thread Starter New Member

    Jul 19, 2012
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    Ok.. you prob hate me for this. Ofc I am a total dingbat when it comes to radio.

    Is it possible to swap out the crystal of a basic (ipod) FM transmitter to transmit your audio to lets say 70mhz, instead of 88-108?
     
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
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    No. Those transmitters use a single chip solution that's dedicated to the FM broadcast band by design. It's a BH1417F if you'd like to look it up. It uses a 7.6MHz crystal. I guess you'd need a 5.4MHz crystal.
     
    Last edited: Jul 20, 2012
  3. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    It's possible (depending on the type of transmitter), but there are a lot of variables you need to take into account. First of all, 70 MHz is in the VHF band, which is the frequency at which a lot of television signals are transmitted. For that reason, you'd probably get a fair amount of interference. Also, thinking about the circuit itself, if it's designed to work at a certain frequency, and you change it, things are likely to operate incorrectly. You might even get some unwanted resonance or interference in the circuit itself.

    I guess the main question in my mind right now is, why?
     
    Last edited: Jul 20, 2012
  4. takao21203

    Distinguished Member

    Apr 28, 2012
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    I am not an radio expert but some of these circuits may use varicaps.

    Crystal is used as reference, but adjustment is done with a Varicap. There also might be things like IF oscillators, mixers, PLLs etc.

    Some can accept a different crystal, some sub-circuits won't respond well.

    With older analog circuits yes they can be modified by someone who is good with radio circuits. Modern digital circuits, yes if you have the chip reference sheet, and if you fully understand it.

    I have examined some chips + circuits, but I would even have difficulties to get a reference design working.

    You would need all sort of testing equipment, frequency generator and things like this.
     
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