Date: Sat, 16 Mar 2002 07:40:36 +0900 From: Brenda Ann Newsgroups: alt.radio.pirate Subject: Re: Newbie FM Transmitter (Newton Braga) I've built many many of these little circuits (variations on a theme), and they are usually good to about 100 to 150 feet in an urban area. The trick is the tuning. First, you don't use a metal screwdriver to tune it, use one made of plastic, or, at most, a metal-tipped plastic one, to do your tuning, or you will get very severe "skin effect" inductance.. which you observe as a change in frequency when you remove the screwdriver. Second, these little transmitters are VERY dirty.. and what you are most likely finding when you can only hear it 2" away is one of the dozens of spurs these things put off, some can be quite strong, and can actually give you nearly 1/4 of the range of the fundamental frequency. What you want to do when tuning it, is to have your radio across the room, with the antenna down. The best method is actually to use a home stereo system with the antenna disconnected. Tune very slowly through the range of the trimmer till you hear the carrier on the stereo THEN apply modulation to see if it sounds good. If you never get a STRONG carrier, then you are not tuning to the proper frequency. Move to the bottom of the dial, and see if you can tune to that area. If you can, then you need to simply spread the turns on your coil about 1/8" or so, and try the high end of the dial again. Important: Your antenna is a part of the oscillator circuit. It should not be more than about 1' long, or it will detune the circuit badly, and you will cause a LOT of splatter. Also, don't overmodulate... these circuits are capable of very wide modulation... over three FM channels worth.. listen to another station, and try as best you can to match the volume of that station. If in doubt, run a little LOWER modulation level, or you will receive distortion on your radio, and possibly complaints from your neighbors about the interference you are causing. To see what I am talking about, simply try this once you have found the proper frequency... tune your FM radio across the dial, and see how many places you can receive your signal weakly.. you'll be surprised.. and it's also coming in on several TV channels, too.. :)