Simple Phone Transmitter Circuit

Simple Phone Transmitter Circuit uses few parts, as it take sound from phone talk and changes to signal and also signal goes far using antenna.

Furthermore, this circuit is easy to make and works well with landline phone.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors	10k, 47k, 330Ω (1/4 watt )	1 each
Capacitors	Ceramic 47pF	3
Semiconductors	Transistor BC547	1
	Diodes 1N4148	4
	Inductor Coil inductor, 7 turns using 0.5mm wire, 3mm dia.	1

This device take voice from phone talk and it changes voice into signal for other electronics; also, it work only in short distance and uses phone wire like antenna.

Below is how circuit work:

Four diodes D1 to D4 make bridge and it change AC to DC for power.

Transistor Q1 with R1, C1 and coil make oscillator and this oscillator give high frequency signal based on coil and C1.

C2 send audio signal to base of Q1 and audio change the high frequency signal (modulation).

Q1 and coil make signal strong and send out and C3 help to adjust signal frequency.

Formulas:

Colpitts oscillator made by transistor Q1, R1, C1 and coil L1, as it give high frequency signal.

Formula for frequency is:

f = 1 / (2π * √(L1 * (C1 + C2)))

where:

• f is frequency in hertz Hz
• L1 is coil value in henrys H
• C1 and C2 are capacitor values in farads F

Note:

This formula work for ideal parts but real parts are not perfect so frequency may be little different; hence, for better result use SPICE software or also count transistor base capacitance.

How to Build:

To build a Simple Phone Transmitter Circuit follow the below mentioned steps for connections:

• First, connect Q1 collector to (+) supply through coil, connect Q1 base to capacitor C1 and then connect Q1 emitter to ground.
• After that, put R1 and R2 in series from (+) to (–) supply.
• Now connect one side of C2 to coil and other side to Q1 emitter.
• Then connect C3 from (+) to (- ) supply and also connect R3 from (+) to (–) supply.

Caution:

• Be careful while using radio transmit device without license may be illegal and check the local rules in your areas

Conclusion:

Overall, Simple Phone Transmitter Circuit changes voice to electric signal to send, but it is not the same like radio transmitter for sending phone talk.

So be careful to not mix both.