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Fm Transmitter

Discussion in 'Electronic Basics' started by DG, Oct 16, 2003.

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  1. DG

    DG Guest

    Brand new to this, i wanna build a transmitter,

    Operating frequency: 150 to 216 MHz

    FM deviation: + or - 15 KHz

    Operating Frequency: 150 to 216 MHz

    RF Power Output: 50 mW

    Whats the best way to go about this, PLL? capacitor/coil?

    Any suggestion on stuff? and refernces to site? Dont know much, plan to
    learn but at the moment want easy fast solution.



    Thanks
     
  2. John Fortier

    John Fortier Guest

    Easy fast solution?

    Sorry, there isn't any. Unless you actualy find out the necessary
    background information you'll be working in a "monkey see, monkey do"
    fashion, and won't be able to correct the inevitable problems which will
    occur while you build and test this transmitter.

    Further, have you checked the licencing situation with regard to this
    transmitter. Will it be legal in your area?

    You might try going to your local Radio Shack, or equivalent, and seeing if
    they have any kits available with these specifications, but again, check the
    licencing situation.

    Assembling a kit won't really teach you anything, though.

    John
     
  3. Joel Kolstad

    Joel Kolstad Guest

    A PLL (assuiming a crystal or other suitably stable reference) will just get
    you a nice, stable carrier. What's your application? If it's just for
    hobbyist uage, you probably don't need the complexity of a PLL.

    You'll find that modifying the scads of designs on the web for 88-108MHz FM
    transmitters to instead run 150-216MHz is easy. As for the +/-15kHz
    deviation -- you'll see a lot of designs out there that _don't even use
    something like a varactor diode_ to thereby allow a (readily) predictable
    deviation with input voltage -- the simplest designs merely change the bias
    of the transistor (that's serving as the 'negative resistance' for the
    oscillator) and... poof!... the frequency of oscillation changes. (Arguably
    it's due to reverse biased junctions in the transistor _acting_ like
    varactors, it's just very difficult to predict the magnitude of these
    changes.) I.e., if you really do need a specific deviation, look for a
    design where it's clear what mechanism is being used to achieve the
    deviation!

    Finally, for 50mW of output power... that's enough power that -- while I
    wouldn't be surprised to see someone having done it one transistor -- it's
    easiest to generate your RF and then add an adjustable gain buffer amplifier
    afterwards to obtain it. Unless you have a low power wattmeter lying
    around, though, you'll have to infer how much power is getting out to your
    antenna based on measuring, e.g., current and voltage through the amplifier.
    Or build your own low power wattmeter.
    Try some of these:
    http://braincambre500.freeservers.com/
    http://ourworld.compuserve.com/homepages/Bill_Bowden/homepage.htm#menu
    http://www.commlinx.com.au/transmitters.htm
    http://www.uoguelph.ca/~antoon/circ/circuits.htm
    http://sound.westhost.com/project54.htm
    http://tacashi.tripod.com/elctrncs/smplfmtr/smplfmtr.htm

    ---Joel Kolstad
     
  4. These freqs are in the middle of the TV broadcase bands, and below 174
    MHz, in the public service bands. In many countries, this power is
    not allowed without a license. For narrow band FM, you would probably
    be best off with a PLL design. Check on the newsgroup
    alt.radio.pirate for more information.

    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
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  5. Radio Scrap withdrew those TXes from the market, apparently at more
    than a gentle nudge from The Flunked Clown College.
    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  6. That's easy to do. A 50 ohm load with 1.5V RMS across it gives about
    45 mW. So if you use one of those grain of wheat bulbs from radio
    Shaft that are rated 1.5V at 25 mA, it will give an approximate
    indication of the power output.
    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  7. DG

    DG Guest

    Thank you.
     
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