Frequency Modulation

Discussion in 'Wireless & RF Design' started by RizwanFM, Aug 24, 2016.

  1. RizwanFM

    Thread Starter New Member

    Aug 24, 2016
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    Hi,
    I wanted to design a Frequency modulation circuit, i'm using a frequency synthesizer (adf4360-8) to create a frequency band of 20MHz which i'm using as my carrier and i'm generating a sine wave of 6KHz which is my information signal. I want to modulate and transmit them. Which modulator IC should i use that can take these two signals as input and give a frequency modulated signal as an output ?
    Or any help regarding the circuit is welcome or any suggestion how should i do it?
    Thank you.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The minimum output frequency of the adf4360-8 is 65MHz so I don't see why you want to try to use it at 20MHz.

    Here's a simple FM modulator you should be able to modify to run at 20MHz.
     
  3. RizwanFM

    Thread Starter New Member

    Aug 24, 2016
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    Thank you for your reply, and just to make it clear i'm not using adf4360-8 at 20MHz. I'm producing a 20MHz band ranging from 88MHz to 108MHz and i'll be using 13 different frequencies from this range as my carrier step wise.
     
  4. RizwanFM

    Thread Starter New Member

    Aug 24, 2016
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    Hi, in simple words i want to modulate two signals, one is varying from 88-108MHz(carrier) and other is of 6KHz(information). How to modulate them?
    Thank you for your response i've very weak RF basis so help kindly.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
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    The method described in the paper liked below can be used to generate phase modulation, which is a lot like frequency modulation. I am not sure that this works well at 100 MHz, but you might find it useful background.
    www.scomcontrollers.com/downloads/lcphasemod.pdf
     
  6. crutschow

    Expert

    Mar 14, 2008
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    What do you plan to do with this signal?
    If you plan on transmitting it any significant distance, that could get you a call from the FCC.
     
  7. RizwanFM

    Thread Starter New Member

    Aug 24, 2016
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    hahaha thank you for your concern :) I know about that i'm not doing anything that would get me or anyone around me in any sort of danger.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    There are various TTL VCO chips that will work in that range and probably CMOS types too - might be 74LS629 or something in that number range.
     
  9. RizwanFM

    Thread Starter New Member

    Aug 24, 2016
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    My 20MHz frequency band range is from 88-108MHz which is carrier signal and information is of 6KHz whereas 74LS629 frequency range is from 1-25MHz
    Can you recommend any chip ?
    Thank you.
     
  10. DickCappels

    Moderator

    Aug 21, 2008
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  11. ian field

    Distinguished Member

    Oct 27, 2012
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    Any logic family will be in the ECL variety for that range.

    You may have to look at manufacturers like AD for an off the shelf chip.

    There is a new development board with similar form factor to the likes of Arduino, Pi etc that was created for instrumentation purposes. Radio Hams are adopting it to program as a transceiver - but I can't remember the frequency limit.

    DDS is an option - but could get a bit spendy at that frequency.
     
  12. radiohead

    Active Member

    May 28, 2009
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    Here's a simple AM radio transmitter that uses a few parts that you can harvest from "unwanted" electronic items. This site doesn't theory you to the point where you don't care anymore, but looks at it from a science point of view. Beginners have to start slowly and build the blocks of knowledge as they go, starting with easy "confidence" projects that require only a few parts for the projects that actually work. My advice: start simple then work on the difficulty level.
    http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
     
  13. bertus

    Administrator

    Apr 5, 2008
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