Venture onto the great rc cars communications world

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Wireless and rc cars channels communications can be great. These types of communications are governed by the rules of each country, so what should not exceed certain limits, the omission of such limits is punishable by fines and penalties.

The miniature FM transmitter has been designed in such a way that does not exceed such limits on their frequency of oscillation which is comprised between 88 and 130MHz and the field generated by the irradiation, does not exceed 50 mV per meter at a distance 15cm of the circuit.

If you join the rc cars circuit following the specifications below you will not exceed these limits, since any changes made to the pro circuit including such a variation in supply voltage, change the scope of the signal. Finally you need to solder the microphone, taking into account their polarity, the antenna and connector for 9V battery respective sprats and secure the battery holder using the screws.

Operation

The transistor Q2 is the oscillator, Q1 is the amplifier to modulate the signal. The modulating signal is applied to the base of Q2 via C2, R6. The capacitors C6 and C7 are part of the oscillator. Q2, L1, C5 form a voltage-controlled oscillator circuit, which is modulated by the audio voltage, is amplified by Q1. C5 is used to tune the oscillator circuit by setting the frequency of oscillation. C8 acts as a filter capacitor.

Once you are sure that all rc cars components have been assembled properly, you can proceed with the testing and calibration of the radio car model circuit. To do this, place a FM radio near the circuit, find a point on the dial in silence (no radio) and receiver volume up to a point where you can hear the interference.

Connect a 9V battery to the circuit and listen to the radio. Slowly and with the help of a small screwdriver, adjust the condenser (trimmer C5) until the receiver is heard a whistle or sound similar, which means that at this point has been tuned to the transmitter frequency dial. You can then speak into the microphone and be heard on the radio the talk.

If the selected frequency is not achieved good reception, repeat this procedure at another point on the FM band. Alternatively, instead of varying the capacitor, tune the radio to find the point where you feel better reception (silence). If after doing this, tune the rc cars transmitter fails, you can adjust the coil that forms the oscillator circuit pooling their turns to raise the frequency, or separating them if you want to reduce it a bit.