2 km FM transmitter
Description.
With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.
Circuit diagram.
Notes.
- Assemble the circuit on a good quality PCB.
- The circuit can be powered from anything between 9 to 24V DC.
- Inductor L3 can be a VK220J type RFC.
- For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L3 and that will be L2.
- Frequency can be adjusted by varying C9.
- R9 can be used to adjust the gain.
- For optimum performance, value of C8 must be also adjusted.
- Using a battery for powering the circuit will reduce noise.
hello sir i want to get updates from your website often
Please sir, (referring to the 2km fm transmitter), how is the capacitor C5 connected, is it connected to resistor R5 or grounded. because i am confused.
Reply to Adex
One end of R5 is connected to the base of Q3 and other end is connected to the viper of POT R9
matching mic
what about L3,how cam i make it?
Please sir am a little confused is c5 and r9 grounded,and is l2 together with l1.
R9 is a potentiometer (POT) and it has three terminals, two end terminals and a wiper terminal.One end terminal of C5 is connected to the wiper of R9 and one end terminal of R9 is connected to ground.Other end of R9 is connected to the collector of Q2.
Thank you sir,sir again L1 and L2 and they connected together because i don’t see any wire that cross.and c5 and r9 can you leave them like that or they must be grounded.
Hi L1 and L2 are primary and secondary of RF transformer. This is for impedance matching of antenna with the tuned circuit(tank circuit). Admin has given a clear reply for your question on C5 & R9. C5 should be connected to the slider (center point) of the potentiometer, and one end (cold end)of the potentiometer connected to earth (-ve common rail)the other end (hot end)connected to R7 Q2 collector junction. R9 is for proper modulation of audio signal. by varying R9 slider from cold end to hot end it can be achieved.
Can you please share some information on the construction of the antennae to be used in this circuit
Reply to Ray
A 1 Meter copper wire will do the job. Do some experiments with the length for getting optimum performance.
Which transistors we can use in replacement of these (BC109, BC177, 2N2219) transistors
possible substitutes for BC109 are 2N2222, BC546, BC547, BC548 etc.
possible substitutes for BC177 are 2N2907, 2N2905, BC556,BC558 etc.
possible substitutes for 2N2219 are 2N2222, 2N2221, 2N2219 etc
Reply to Mohamed
Check this link
http://www.circuitstoday.com/how-to-make-an-air-core-inductor