From: d1gunnar@dtek.chalmers.se (Gunnar Andersson)
Newsgroups: sci.electronics
Subject: ** FM-transmitter **  Here are the Schematics!!!
Summary: Schematics for a MONO FM-transmitter
Date: 18 Oct 91 15:44:57 GMT
Organization: Chalmers university of technology, Gothenburg Sweden

Hi guys!!

A while back a couple of people requested information on an FM-transmitter
circuit.  I mentioned that I could post a design without any IC's if there
was enough demand.  I got a bunch of mail so I guess there was.  Because of 
this I have written a file containing the schematics and some info.  Here it
is:  Enjoy!!

*******************************************************************************

    Mono FM-Transmitter Schematics:
    ===============================

      *----- L1 ------*--- R1 -----*----* +12V (Approximately)
      |               |            |
      *---- C1 -------*            |
      |               |            |
      |   (c)         C3           R2
      *---|           |            |
      |   *  (b)      |            |
     C2   T1 *---*----*------------*    
      |   *      |    |            |
      *---|(e)   |    |            *
      |          |    C4      Signal Input here!  
      R3        R4    |            *
      |          |    |      +     |
      -----------*----*--- C5 -----*
                      |
                    (GND)

          Component-list:
          --------------

        R1,R3   560 ohm       
        R2      10  Kohm
        R4      2.2 Kohm

        C1      2-22 pF variable cap
        C2      10 pF
        C3,C4   2.2 nF
        C5      33 uF 
        T1      547B  (Any similar NPN transistor, really)

        L1      Make your own inductor:  Wrap 1.5 - 2.0mm thick copper wire
                6-7 times around a pen/pencil or similar object.

        Notes:
        ------
 *  This is a MONO transmitter!  A stereo Tx will require a more complicated
    design.
 *  The operating voltage is not critical. It could work on voltages as low as
    5V.  At least a 9V battery is recommended. 
 *  Use the variable capacitor for tuning (or alter L1 I suppose).
 *  The original design suggested using a microphone directly on the input.
    I don't know if this works but feeding it with any medium-level signal
    (e.g. a CD-player or TAPE output will work although it has a lot higher
    output level than a microphone does.
 *  REMEMBER! Using this transmitter could be ILLEGAL!!
    (As usual I will not be responsible for ANYTHING you do, blah, blah etc.)
    All legal aspects aside: Be considerate of others!!!
 *  Finally I would like to give credit to someone who calls himself 
    "Slice of Genix" as I think he was the one who came up with the original
    design.
 *  This file written by:
    Gunnar Andersson
    Chalmers University of Technology, Sweden. 
    Mail me at:  d1gunnar@dtek.chalmers.se

*******************************************************************************

I am interested in info concerning the output power of this baby and how to
control it.  Some people who use it for transmitting short distances inside
their house may want to decrease the power so that it won't bother anyone
else.  Others may wish to increase it.  I am interested in both things.
If you can figure out how to control the power or have any suggestions for
improvements, please mail them to me.

/Gunnar Andersson
d1gunnar@dtek.chalmers.se

******************************************************************************


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