FM transmitter with a range of 1 km!! Perhaps the beginning of each building attracts electronics

FM transmitter with a range of 1 km!! Perhaps the beginning of each building attracts electronics "bedbug", a small FM transmitter. VA Radio was already several such simple zapojeníček published, but almost always been their reach just a few meters when they were powerful, and again were beginning to radio amateur merca too complicated. merca Figure 1 is a schematic diagram of a simple FM transmitter, which contains only three common transistors and its range is somewhere around 1 km!! The input is connected electret microphone MIC, which has found itself integrated amplifier. He is fed through resistor R1, and if you use a dynamic microphone input, you must disconnect the resistor. The signal from the microphone is fed through a decoupling capacitor C1 to the base of transistor T1. It is common emitter configuration and is responsible for the weak audio signal from a microphone to amplify. merca Its operating point is set by the feedback resistor R2 and should be determined according to the supply voltage used, so that the base of this transistor has a voltage of about 5V. For this transistor is connected capacitor C3 to remove high frequencies. The amplified audio signal is fed directly merca to the base of the transistor merca T2. That again is in common emitter configuration and operates as RF oscillator. Its frequency is given by the LC circuit connected in the collector, a coil L1 and a capacitor C5. The frequency at which this 'bedbug' broadcast is therefore fixed and can not be changed, because it is a surface coil and capacitor technology is not rotating. This feature, however, usually does not matter. But if the radio frequency transmitter cover any other, it can be two pieces of wire with a little reduced. This reduction is accomplished by taking any two pieces of wire (the wire but it must be hard to bend the straightened himself), and smotají to each other. This creates a kind of a small capacitor, which is then solder from the circuit in parallel to the capacitor C5. This creates a parallel connection of two capacitors whose capacity will be higher than the original one and it will all LC circuit merca to oscillate at a lower frequency. This reduction in transmission frequency is, however, possible only a few kHz, we need if our small transmitter tune somewhere else, it is preferable instead to engage the trimmer capacitor C5 and then whenever the transmitter retune. It is also possible to adjust the plate and place it on an ordinary coil. The coils would then be made of enamelled wire having a diameter of about 0.7 mm. Or just from that what you have at hand, but may be too weak. The coil is wound itself must hold its shape and will not unravel. It is wound on a 5mm diameter and has about 5 turns with turning on the first thread. After the solder can be the stretching and compressing merca change frequency, merca so there is no need to use a tuning capacitor. The entire product is then placed in proximity of our transmitters and two antennas are mounted so as to be perpendicular to the ground (vertical). S meter antenna is not doing anything, but the transmitter is different bends and rotates until the multimeter shows a maximum value. I am in my experiment had finally antenna merca slightly bowed to the ground and about half bent even more. You just need to play around a bit with the transmitter but then its range, in spite 1.5 km!! Below is a picture of the plate and its installation, the plate may be necessary, amended, to use when tuning capacitor or coil of wire. Subscribe entire circuit is about 30 mA at a supply voltage of 9V. P ro increase transmitter power can be increased its power supply voltage up to 15V, but it will also increase its consumption, but that in most cases does not matter much.
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