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2-5 Km Long Range FM Transmitter
Posted on Friday, June 24, 2016   •   Category: FM Transmitters

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. This will likely encompass 5km spectrum (long range). 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. The output strength of this long range rf transmitter is approximately 1W. Transistor T1 is employed as an oscillator stage to present a small power steady frequency. To fine-tune the freq. apply the 10k linear potentiometer this way: should you moderate, in the direction of ground, the freq. would probably decrease but when you fine-tune it in direction of + it would climb. Essentially the potentiometer is needed just as a flexible power source for the a pair of MV2019 varicap diodes. Both of these diodes function as a changeable capacitor whilst you regulate the pot. By tweaking the diode capacitance the L1 + diodes circuit renders a resonance circuit for T1. Feel free to employ transistors similar to BF199, BF214 however be careful not to use BCs. At this point you donít 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.

0-30V Mini Bench Power Supply
Posted on Thursday, June 2, 2016   •   Category: Power Supplies

After many years of employing this ugly and clumsy bench power supply, I decided it was time to build something better, smaller and nice looking. It began as a variable power supply based on an LM338 5A voltage regulator and external power adapter. LM338's Data Sheet has several very helpful application notes and circuits. I chose one that illustrated variable output and included protection diodes. Diodes are included to protect the regulator from damage in case the input is accidentally shorted to ground. This is a distinct possibility if using jumpers to attach it to the power supply. Also the output of station supply may be shorted if some other device fails. Without the diodes, if this happens, the capacitors will dump their charge back through the regulator. Since the current spike may be many amps, the regulator may fail. The diodes steer the current around the regulator and into ground, thereby protecting it from damage. With adequate input the LM338 makes a fabulous variable power supply. This small supply is user friendly and fits nicely on my cluttered bench.

Pen FM Transmitter Bug
Posted on Friday, May 20, 2016   •   Category: FM Transmitters

Pen FM Transmitter bug projects have been very popular. The idea of being able to hide a transmitter in a pen is very appealing. In an effort to reduce the size of this design, we have used surface-mount components. Firstly, the thought of using the coil in the tank circuit for transmitting RF was a little far fetched, but we used it as an example for those who were interested in experimenting with our circuits. Now we have gone back to a conventional antenna, the whip. The whip or straight-line antenna can be coiled, wound longitudinally or folded. The way it is wound makes a big difference to its effectiveness, but when you are limited in space, you have to accept these limitations. Even though we have used this antenna set up in our previous pen bugs we have considerably improved the circuit to the point were it has low battery consumption, but high RF output. The size of this design has been reduced considerably by using surface-mount components.

76MHz - 110MHz FM Transmitter with Booster
Posted on Monday, May 16, 2016   •   Category: FM Transmitters

Three stage FM transmitter with an on board signal booster for increased transmitting range. It broadcasts audio on 76MHz - 110MHz FM frequency via included on board microphone or from MP3 player, Phone, iPod, Computer, Laptop, CD Player, TV, Satellite Receiver via on board 3.5mm connector. It transmit sound with excellent clarity throughout your home, office, yard, camp ground, etc. Transmitter is supplied by 3-12V DC voltage and uses one 2SC9014 and two 2SC9018 low noise RF transistors.

Simple Miniature FM Transmitter
Posted on Saturday, April 16, 2016   •   Category: FM Transmitters

I found this FM transmitter circuit on the internet, it works very well and it is very simple to build, even for amateurs. I managed to squeeze all the parts on small 1.5 x 2 cm PCB. When using small wire antenna and 3V power the range is 50m. The coil has 10 turns on a 3 mm diameter and is wound with 0.3 mm copper wire. The microphone is an electret type. Transmitting frequency is changed by stretching or compressing the coil. Furthermore, we can change the frequency by changing C2 capacitor (10pF capacitor with a frequency of about 88MHz, with 8.2pF 95Mhz and 6.8pF 104Mhz). Further tuning to the correct frequency is done through the coil. Transmitter can be powered by 3V button battery.

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