88 - 108mHz Stereo FM trans. <5V, manually tunable when complete.

Discussion in 'Wireless & RF Design' started by Enigmatic Entity, Apr 20, 2009.

  1. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
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    Hi everyone,

    I wish to make a portable FM transmitter that is able to be tuned to any frequency within the FM (radio) band at any time using a pot. Desired range is about 30m. My best bet at this stage is probably the BA1404 version, but I don't know whether it is tunable using a potentiometer. I was wondering if anyone knows of an alternative solution?

    Any reply greatly appreciated; also, if you require more info, please ask and I will try to provide.

    e.E.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
    19
    0
    Most of the (490 000) ones I find are mono, microphone-type transmitters, and/or are not adjustable as in like how your clock radio has a tuning knob. Yes, they are tunable with some inductor/tune and set pot, but once set they are set almost permanently. Then there are those that are (tunable), but require large amounts of power and are not portable, i.e. for an mp3 player. The ones available in stores seem to have a range of about 2m, which is less than ideal.

    The first pic looks like it might do, except it is almost too large and is in a kit. I'm not going to pay heaps to get it sent to where I live.

    The second one is more available, except it will need a modification to make it tunable at any time using an "external" pot.

    Any other versions of the BA1404 or equivalent would also be helpful.

    Thank you for trying to help out,

    e.E.

    EDIT: Also, if there is a way to modify a commercially available transmitter for greater range to 30m, that would do, since there are some that can be tuned all over the FM radio band.
     
    Last edited: Apr 20, 2009
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The simple FM transmitters connect their antenna directly to the LC tuned circuit so the frequency changes when something moves toward or moves away.
    They do not have a voltage regulator so the frequency also changes as the battery runs down.
    They do not have pre-emphasis (treble boost) like all FM radio stations have so their sound heard on an FM radio (they all have de-emphasis) is muffled like your stereo with its treble tone control turned all the way down.
    They are mono, not stereo.
    They are cheap toys.

    The BA1404 is obsolete and had very poor performance. It was replaced by the BH141x family of FM stereo transmitters that use a crystal controlled frequency synthesizer and is used in most of the MP3 to car radio transmitters. The transmitter has an attenuator at its antenna (it can be removed) to reduce the range so it doesn't interfere with the radio in a car beside you.
     
  5. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
    19
    0
    I think I might wait until I get a good enough income and buy a C.Crane, do the mod and be happy. The only thing is, I'll have to get it shipped to Australia, I don't know how long that'll take.
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The Micromitter is a modern FM stereo transmitter kit that is made in Australia. Silicon Chip magazine from Australia had a project about it about 4 years ago.
     
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