Simple FM transmitter circuit.
Two transistor FM transmitter.
Description.
A lot of FM transmitter circuits have been already published here. This just another one, a simple two transistor FM transmitter.The first stage of the circuit is a preamplifier stage based on transistor Q1. This is a collector to base biased amplifier stage where resistor R2 sets the collector current and R1 provided the necessary collector to base bias. C1 is the input DC decoupling capacitor which couples the input audio signal to the Q1 base. C8 is the power supply by-pass capacitor. Next stage is the oscillator cum modulator stage built around transistor Q2. Electrolytic capacitor C2 couples the output of the first stage to the second stage. R3 and R4 are the biasing resistors of Q2. R5 is the emitter resistor of Q2. Inductor L1 and trimmer capacitor C5 forms the tank circuit which is necessary for creating oscillations. The modulated FM signal is available at the collector of Q2 and it is coupled to the antenna using capacitor C9.
Circuit diagram.
Simple FM transmitter circuit
Notes.
- The circuit can be powered from anything between 6 to 12V DC.
- Using battery for powering the circuit will improve the performance and reduce noise.
- A 9V PP3 battery is a good option.
- If you are going with a battery eliminator, then it must be well filtered and regulated.
- Trimmer C5 can be used for adjusting the transmission frequency.
- Antenna can be a 1m copper wire.
- L1 can be constructed my making 4 turns of 1mm enameled copper wire on a 10mm diameter plastic former.
- Trimmer capacitor C6 can be adjusted for obtaining the maximum range.
- Most of the components required for this circuit can be procured from your junk box.
can i use a electrct condensor mic in place of audio in?
I want more explanation to get the output of this CKT when we run it in laboratory.when i was going to run it the output of L1 & C5.what i want to do?please reply me.
how to find the transmitting frequency
give me the specifications of antena..
INductor is availble in market or not..?
audio in with a mic rite?
please help me with the circuit diagram of 2km of fm transmittes.thanks from your boy
sir, can you please tell me the use C3 and C4 capacitors ..???
actually i am going to build one,but theoretically i am not able to find out the use of these two capacitors,
Someone please help me …
C3 and C4 are for suppressing the ripple if any. And by ripple I mean any ac components. C3 prevents any noise disturbance to pass into the input of transistor Q2. and C4 suppresses voltage spikes and noise disturbance in the powersupply. Always in small circuits, typically a 100nf condesor will be connected from supply to gnd to bypass the unwanted ac components.
I need to know how to make this tuneable. Any help would great. Also I am new at this kind of thing so please make it as simple as possible.
Hello sir can i know the frequency at which this circuit works
Hi Seetharaman,
Can i use BC107 instead of BC108~? pLease reply ASAP thanks
please i want a answer about FM transmitter……what is the function of FM transmitter in analog modulation?????????????
Appreciated,
Hi Sujeesh you have to use a non metalic screw driver to adjust the trimmer. may be an ebonite rod tip filed similar to screw driver’s tip will be the best.
Sir,
i made a fm transmitter similar to this circuit.and i can’t tune it correctly.it have one 20pf trimmer and while tuning it made clear reception when i touch in variable resirtor in the circuit.but when i don’t touch it,it will not make clear reception,can you help me? How can i make clear tuning?
Hi This transmitter range will be similar to 200m FM Transmitter. The tunable frequency range can be between 80 & 150MHz with the adjustment of both L1 coil and trimmer C5.
what wiil range of this circuit ? &
which frequency it will transmit ? &
how we change the frequency and range of this circuit ?
what is the frequency range of this circuit?
Thanks.
Hi Ashnuka for BC108 you can use BC548 or 547 or any low noise NPN transistor but for 2N2369 you have to use 2N2219, 2N1711 or 8050
What are the replacements for both transistors?Can i use BC547 or any npn?
how to prepare our own antenna?
@M
For long range transmitters – follow these links:-
http://www.circuitstoday.com/2-km-fm-transmitter
http://www.circuitstoday.com/long-range-fm-transmitter-1
Short range:-
http://www.circuitstoday.com/200m-fm-transmitter
@Rajkumar
This is a two stage FM transmitter. First stage is the preamplifier stage where the input audio is amplified for transmission.This stage is served by transistor BC108. Second stage is where the amplified signal is modulated to a carrier wave (produced by tank circuit L1 and C5). This modulation stage is served by transistor Q2 (2N2369)
Why two different transistors are used for?
how to test ckt using multisim?
I have working multisim and proteus simulations of above FMT those who requires mail me @ harbindersidhu@ymail.com
Hi, how much distance is this circuit can deliver?
In theory C3 and C6 capacitors will cause damage to transistors. When transistor tries to saturate it will try to reduce the voltage across the capacitors to zero. However, if the capacitors are charged a large amount of current will flow into the transistor.
An FM transmitter must have a modulator. All I see it amplifiers and filters.
Forgot:
-How do i make this transmitter stronger?
-Thanks again!
How long range is this transmitter for?
How strong is the efect? (mW)
-Thanks!
Hi, how much distance is this circuit can deliver? this is a good circuit, that requires only minimum of parts from “junk box”
Thanks in advance.
Iam already going to build tone detector by using NE567, to detect this circuit frequency .
So please can you define the Frequencey of this Transmitter ?
and it’s calulation equation ?
In abrief I need Fo .
Thanksssss alot
Nafez Fares