FM Broadcasting

Posted on Feb 5, 2014

Metal enclosure, forget the plastic case they sell, it`s nearly useless. ( I made a box from copper PCB that I soldered together, it works okay, but could be better. ) Ground it to the enclosure well, and connect everything to a good earth ground. 4. Make sure you have a well filtered/regulated power supply. I put a 7812 regulator on the underside of the board. I also added

FM Broadcasting
Click here to download the full size of the above Circuit.

more filtering capacitance for kicks. (Using free Sanyo Os-Con samples!)Also, you can replace the diode string for the BA1404 with a regulator, just don`t go over 3V! You can also ditch the balance control, replace it with a 50K resistor. If it isn`t exactly centered, it can screw with the stereo pilot, and stability. (put it across the two pins on the chip, don`t use the + connection, as you would on the potentiometer. I havn`t actually tried this yet, but this is what the data sheet says. ) A note on changing/moving level controls, etc, Using excessive wire length for anything can result in noise, instability, feedback, etc! I advise that you keep all parts closely soldered to the board, and for example, don`t move the level controls to the front panel with any length of wire. I did the well covered 70mw mod. Tack soldered a 2N2222/2N4401 circuit on the underside of the board. Got 70mw output. covered a fair area(half mile radius), with a 1/4wave vertical groundplane antenna hanging from my bedroom ceiling. Not bad! I can get a solid watt into a dummy load, but only 900mw or so into my coax (and even less *at* the antenna. ~750mw, and thats only about 10 feet of RG58!) Good coax is a wise investment, don`t skimp here! mini RG-8 is okay, there are others that are better. Try and keep cable runs short and connectors, etc. to a minimum to avoid extra losses. When transmitting with such low power, every little bit helps! ;-)...

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