Local Oscillator Design (heterodyne) for FM reciever

Discussion in 'Wireless & RF Design' started by J.o.s.h, Oct 8, 2014.

  1. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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    Hello, pls i need help on the desingn of the above stated project. i really cannot tell what heterodyne means and how to go about the whole design, including design of power supply for the circuit. pls help as soon as possible. FETs would be appreciated. tanx in anticipation
     
  2. b1u3sf4n09

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    May 23, 2014
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  3. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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    oh well tanx for posting, but ive read the wiki site b4, at least some of it. i do understand what "heterodyne" means. my aim is to design a local oscillator for fm reciever using a FET , using any convenient oscillator type. any circuit diagram with explanations would do.tnx
     
  4. b1u3sf4n09

    Member

    May 23, 2014
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    Dang, now that's some fast learnin'...

    In all seriousness, your request is not a small task. Engineers are paid large (*cough) amounts of money to design the circuit that you are requesting. Maybe if you could define the radio you want to build (frequency, power), we could help you get started.
     
  5. bertus

    Administrator

    Apr 5, 2008
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  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    why not use an se602 chip? a built in oscilator and mixer.
     
  7. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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    oh tanx every1 for suggestions
    i have been constrained to use FETs for the LO
    I have a picture copy of a local oscillator (voltage controlled) for FM reciever but built with BJTs. i would appreciate if any one can EXPLAIN the circuit to me and suggest how to introduce FETs in place of the BJTs. the full document can be found on this link. http://www.eit.lth.se/fileadmin/eit/courses/eti041/VT2011/04a.pdf
     
  8. DickCappels

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    Aug 21, 2008
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  9. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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  10. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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    hello please i would love to have a clapp instead of the colpitts. i need to hit frequency of 119mhz but I am still around 2mhz wit this cct.
    osci.PNG
    can anyone advise on the values of capacitors and resistors thatll give the req. frequency?
     
  11. k7elp60

    Senior Member

    Nov 4, 2008
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    I would recommend changing c2 and c5 to approximately 30pf, and changing c6 to 30pf and L2 to 6uh.
     
  12. J.o.s.h

    Thread Starter New Member

    Oct 8, 2014
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    I ended up with a somewhat unstable triangular waveform of about 50khz.
     
  13. k7elp60

    Senior Member

    Nov 4, 2008
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    The only other things I can suggest is to remove C1 and D1, Change C9 to 100pF and where L2 connects to R2 replace that junction with a 1000pf capacitor.
    One important thing is the construction, it needs to have short leads from each component. Building it on a solderless bread board will not work. You may have to increase the supply voltage. If you have an adjustable power supply increase the voltage to about 9V.
     
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