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another FM transmitter project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by hannobisschoff@gmail.com, Apr 14, 2011.

  1. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    4w_fm.gif

    This looked like a nice transmitter to build when I came across it on the web. But only later did I see it uses a negative -3 V power supply, and a hard-to-get ferrite core coil.
    All I want to know is how to create a +4 and a -3 v supply that I can use, and how could I substitute the ferrite beads with 6 holes.
     
    Last edited by a moderator: Jan 26, 2014
  2. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    the ferrite beads are RFC1; 2; and 3
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It doesn't specify the voltage rail (there's only one!) on that circuit - those are just pin numbers, notice 1, 2, 5 and 6 are there as well.
     
  4. dave

    Dave New Member

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  5. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    Nigel goodwyn, are you saying that the bottom rail is in fact ground, and that "line" 4 goes to an unknown + voltage that is not given on the schematic?

    If so, that solves the supply V problem.
     
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, the diagram makes no claim that those are voltages (and would make no sense if they were), they are obviously simple pin numbers for connecting off the board
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The extremely old circuit is a Smartkit from Greece and is posted at Electronics-Lab 4 Watt FM Transmitter
    Its single-polarity supply is 12V to 18V.
    It is designed to use a very old "crystalic microphone" and needs a modification to use a modern electret mic.
    It does not have pre-emphasis like all FM radio stations have so it will sound muffled without high audio frequencies on any FM radio.
     
  8. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    would it work if I used the mic input to feed an audio signal into directly, or would I have to match the impedance to a crystallic mic. If so, HOW.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    An audio signal has a much higher level than a mic signal so an attenuator is needed.
    A 4W transmitter is illegal in most countries without having a licence to operate a radio station and that poor quality old circuit is not good enough to be a radio station anyway.
     
  10. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    Thank you, the circuit is only as an intro into RF. And besides, I'd rather be a guy that prefers science to abiding the law.
    I'll google a suitable attenuator. BTW you specifically have been helpfull at this site, since when have you been interested in this wonderfull world (hobby?) of electronics?
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You must not break the law with a poor quality high power transmitter because it causes all kinds of interference to aircraft communications and guidance signals, FM radio, TV, police, ambulance and fire department radios.

    Make a radio instead of a transmitter as an intro to RF.

    I began playing with electronics about 55 years ago. I built an AM radio about 51 years ago. I built an FM tuner and amplifier about 49 years ago and I built an oscilloscope about 48 years ago. I built a low power FM transmitter about 47 years ago and built a much better one 6 years ago. My entire career was in electronics, mostly sound systems.
     
    Last edited: Apr 16, 2011
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  12. killivolt

    killivolt Well-Known Member

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    That wasn't the right thing to say to the guru.

    Just listen and learn to experience and the sheer weight of knowledge. It can't be obtained otherwise.

    But, "that" was a good question to ask "since when have you been interested in this wonderfull world (hobby?) of electronics?

    " Weed Hopper" what were you thinking.

    For him it's not a hobby, he helped build what you want to know. Watch your step.
     
    Last edited: Apr 16, 2011
  13. JimB

    JimB Super Moderator Most Helpful Member

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    A VHF transmitter (4 watts output) is not a good place to start for someone who has to ask about the supply voltages and connector pin numbers.

    OK fair enough.
    Just consider how you would feel if some numpty just down the road was pratting around with such a device and metaphorically vomited spurious signals all over the radio programme you were trying to listen to or blanked the screen on your TV?

    Since you ask, as a hobby about 50 years, professionally in various capacities just over 40 years.

    JimB
     
    Last edited: Apr 16, 2011
  14. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    Yes JimB, you have a point. I'm thinking I'll just let go of this circuit and start looking for a better (maybe weaker as well) one. But the problem is, none of these cheap 2n2222 or 2n3904 "Transmitters" work. they all just seem to jam and osscilate through the whole bandwidth. Another question I have, is should I rather try AM, or are FM transmitters better in terms of quality and complicatedness. Can you maybe supply a link to a good quality and not too complicated circuit.

    Thanks.
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your cheap radio was probably overloaded by the nearby transmitter.

    My FM transmitter is made with a 2N3904 transistor as the audio preamp, another 2N3904 transistor as the RF oscillator and a 3rd 2N3904 transistor as the RF amplifier.
    When it feeds a cheap $1.00 FM radio from The Dollar Store its transmission is all over the dial the same as local radio stations.
    When it feeds a cheap Sony Walkman FM stereo radio its transmission is all over the dial when its attenuator is switched to DISTANT but is in only one spot on the dial when the attenuator is switched to LOCAL and is not too near.
    My HI-FI stereo tuner has the transmission in only one spot on the dial.

    AM sounds terribly distorted even though all high frequencies above 3.5kHz are missing. Also it is mono not stereo.
    A half decent FM radio has a frequency response to 15kHz with low distortion and is in stereo.
    A single pole FM antenna is only 80cm long. But a single pole AM antenna must be 8000cm long to work the same.

    Look in Google for The Micromitter which is an FM stereo transmitter project using new ICs and the circuit is used in many commercial MP3 to car radio FM stereo transmitters that do not cost much. They have an attenuator at their antenna to reduce the range and interference but it is easily removed.
     
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  16. hannobisschoff@gmail.com

    hannobisschoff@gmail.com Member

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    the problem is, my local electronics store doesn't supply the BH1417F like in the silicon chip magazine. But still, it looks like a nice circuit. I don't want to be a nuisance, but you don't perhaps have schematics of a simpler transmitter that is made of commonly availible parts.
    As always, thanks for the help to the newbies like me.
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    There are hundreds of simple and old FM transmitter circuits using US and European common parts on the internet. Most are toys with very poor performance.
    You don't show where you are so I can't help you.
     
  18. killivolt

    killivolt Well-Known Member

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    Silicon chip Magazine is based in Australia. .
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    But the BH1417 IC is supplied all over the world. Digikey in North America has over 8000 in stock today and Farnell has it in 90 countries.
     
  20. tytower

    tytower Banned

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    Err I'm fairly sure you did not mean this as I read it ?
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I wrongly said that a single pole AM antenna must be 8000cm long.
    I should have said that a single pole anranna for the 1MHz AM broacast band must be 8000cm long.
    There are a few AM broacast band radio station antennas near my home. They are HUGE.
     

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