![]() ![]() Try to use no wires in the main functional area (transistor and coil). It consists of 36SWG wire 2.5 turns only in 5mm diameter ferrite rod. ![]() A coil takes care of the output frequency. The circuit has a central RF oscillator NPN transistor BF494 (substitute: BF199). This runs at very low voltage, by a CR2025 3V battery, current consumption is also low.And the total size of this FM transmitter (including battery, excluding antenna) is less than that of a matchbox. This is the most simple and cheap FM transmitter you can ever find. I surrender this circuit to anyone who likes to experiment in things like this. So with the overpass being right around 50 feet in height also, the transmitter surpassed my judgement call on its signal. Well, being on that overpass, if I had a strong telescope with me, I am sure I could see the 50 foot antenna in my oak tree. I now understand what is meant when one says FM signal travels best in a line of sight. When I got to the top of the overpass in my car, the audio signal came in as 'clear as a bell'. With the transmitting antenna at 50 feet above ground, I decided to see how well I could receive the transmitter signal from an overpass than is exactly 15 miles from the transmitter. Like I had said above, right at 10 miles, the unit was at its best giving clear audible audio into the speakers of my car. When I finally did get used to find out where my 'main' frequency was, the unit performed extremely well. ![]() It was thru trial and error, with the FM tuner, in finally finding out how to grab the right frequency. That was, by far, one of the hardest things to capture. Of course, one would be better off with more equipment than I have had to capture the main oscillating frequency. This circuit worked well for me, as I had experimented with it for nearly a year. I had no equipment, other than a watt meter to measure it's power and a digital FM tuner with a 5-LED Signal Strength Bargraph display to use as capturing the main oscillating frequency, which was right at 87.5 MHz. overall distance was 17 miles, but the audio signal was weak. Together with about 70 feet of coax, this transmitter delivered great audio at a distance of 10 miles. I used this transmitter with a half-wave open-end dipole in a vertical position 50 feet above ground. Together with the power amp 2SC1971 / MRF237 / NTE342 it then became a 7W unit. This 7 Watt FM Transmitter was originally a 200mW unit, without the universal power stage added. At this point you don’t receive yet the long range fm wireless transmitter due to the fact that the electric power is fairly reduced, a maximum of 0.5 mW. Feel free to employ transistors similar to BF199, BF214 however be careful not to use BCs. By tweaking the diode capacitance the L1 + diodes circuit renders a resonance circuit for T1. Both of these diodes function as a changeable capacitor whilst you regulate the pot. Essentially the potentiometer is needed just as a flexible power source for the a pair of MV2019 varicap diodes. would probably decrease but when you fine-tune it in direction of + it would climb. apply the 10k linear potentiometer this way: should you moderate, in the direction of ground, the freq. Transistor T1 is employed as an oscillator stage to present a small power steady frequency. The output strength of this long range rf transmitter is approximately 1W. It includes an extremely consistent oscillator for the reason that you employ LM7809 stabilizer that is a 9V stabilized power source for T1 transistor and for frequency realignment that may be reached by means of the 10K linear potentiometer. This will likely encompass 5km spectrum (long range). The proposed long range transmitter circuit really is very steady, harmonic free design which you can use with standard fm frequencies between 88 and 108 MHz.
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