Crystal Osc 30MHz Design or Purchase

Discussion in 'The Projects Forum' started by Fovakis, May 14, 2013.

  1. Fovakis

    Thread Starter New Member

    May 14, 2013
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    Hello experts…i am new in the RF field and i need some help…
    So i have a double balanced mixer (ZAD-6+ of Mini Circuits) that need +7dBm Local OsC power and 30MHz Loca.osc frequency. At the time i use signal generator for l.o

    How can i make a crystal oscillator with these parameters? Can anyone tell me simple how to start? I can buy also some ready crystal osc ?

    Many thanks
    George
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  3. Fovakis

    Thread Starter New Member

    May 14, 2013
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    Many thanks for your reply! So,

    *what is the power output of this crystal?
    *square or sine?
    what is TTL output?can it feed the mixer or i must put any filter after this?

    Regards,
    George
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    The output of a crystal oscillator module is a 0-5V square wave (sometimes referred to as TTL compatible). Add a filter or resonator tuned to the fundamental frequency to turn it into a sine wave.
     
  5. Fovakis

    Thread Starter New Member

    May 14, 2013
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    Hi Mr.Chips,

    the supply of the crystal osc proposed by GopherT is +5volt and i see the datasheet that the output voltage is 0.4-0.5 Volts. There are some probles as i understand to this:

    1) i must match the osc with the filter (maybe with a buffer)
    2) maybe i must put an amplifier to amplify the signal (mixer needs +7dBm)
    3) i must match the output of the filter or amplifier(if needed) with the sma input port of the mixer
    4) i don't know the frequency stability of the signal after all these devices...maybe it will have a large phase noice
    5) i will need a PCB for all these right?

    Regards,
    George
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    You are reading the datasheet incorrectly. The minimum range is 0.5 - 2.4V.
    You will get close to 0-4V. You will not need an amplifier. Just use a tuned LC circuit.
    Frequency stability is stated as +/- 100 ppm. In reality you should get about +/- 5ppm.
    The frequency stability is locked in by the crystal in the module. You will experience little shift with external components.

    If this is for an RF design, you may want to be able to tweak the frequency with a trimmer capacitor. You cannot do this with an oscillator module.
    You may want to look at a crystal oscillator circuit instead.
     
  7. Fovakis

    Thread Starter New Member

    May 14, 2013
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    MrcHIPs you have right the range is 0-4Volt.
    So, about the power i will use a voltage divider right?
    I must use a buffer to make the matching.
    The LC Circuit will be to make the phase noice smaller at around +/-5ppm

    I didin't understand your last three sentences. I want a fixed local oscillator, i don't bother not to be tuned. An oscillator module is an oscillator than i can buy from mini circuits with all the devices we talked about before, ready on it?
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    The oscillator module alone will be stable to +/- 5ppm.
    The signal is a square wave.
    You can remove the harmonics with a simple RC filter.
    I don't know what is your application but at this stage just go ahead and try it. What is there to lose?

    If you told us more about what you are trying to do maybe we can see what are the issues.

    Shouldn't this thread be in the Radio and Communications forum?
     
  9. Fovakis

    Thread Starter New Member

    May 14, 2013
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    Yes you have right it must go to Radio and Commun forum. I will tell it to admin.
    Here is a photo of what i am doing.Check this please....


    [​IMG]
     
    Last edited: May 15, 2013
  10. MrChips

    Moderator

    Oct 2, 2009
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    This is way out of my league. RF is not my field. Get Sue to help you.
     
  11. Fovakis

    Thread Starter New Member

    May 14, 2013
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    Who is Sue?
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Sue is one of our more active RF experts. She'll show up soon enough. You can also post a new, specific question about your whole circuit and put RF in the title. She will be sure to see it that way.
     
  13. Fovakis

    Thread Starter New Member

    May 14, 2013
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    ok i will post right now!
     
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