Wireless transmitter principle circuit diagram

As shown in the figure is the schematic circuit diagram of a wireless transmitter . Q1 is a common-emitter transformer coupled oscillation circuit: the load is the secondary coil of transformer T. After the collector output signal is coupled by T, it is sent from the secondary pole to the base via C1 to form a positive Feedback, vibration. The base is fed a low-frequency modulation signal at the same time to perform amplitude modulation on the generated high-frequency oscillation.

Q2 is a buffer amplifier stage. The output of Q1 is coupled to the base of Q2 ("Q1" on the right in the figure) via C3. L1 is the load inductance of Q2; and is sent to the antenna for emission via the C4/L2 series resonant circuit . R2 is grounded, that is, zero bias. Since the input signal amplitude is large and the frequency is selected by the C4/L2 resonant tank, it is not afraid of distortion and is more efficient.

There should be a connection point at T, L1 and 9V. Since the base of this circuit has no DC bias, the circuit all works in Class C amplification. The phases between the primary and secondary of T are opposite, that is, when the collector current of Q1 increases, the primary induced electromotive force of T is positive on the right and negative on the left, and the induced electromotive force of the secondary is positive on the left and negative on the right, and the charging current for C1 increases. The opposite is true when the collector current decreases. The frequency is determined by the capacity of C1 and the inductance of T.

The transmit power cannot be determined by these parameters now. The voltage is known, but the key is that the current is not known. The current (AC current) is determined by the current of Q2 (the transistor behind should be Q2), the base drive, and the impedance of L1.

When it comes to receiving distance, it is related to receiver sensitivity, propagation environment, antenna height, and antenna gain. Generally speaking, it is an ideal distance, and the actual distance is quite different.