200M FM Transmitter
Description.
A very stable and simple FM transmitter circuit is given here. With a matching antenna, this transmitter can attain a range of around 200 meters. I assembled this transmitter few years and got very good results. Let us see how the circuit works.
A condenser microphone (K1) is used to pick the sound to be transmitted. Capacitor C1 is a DC decoupler and the sound signal is coupled to the base of Q1 which wired as a preamplifier.R2 and R3 are the biasing resistors of Q1. Amplified sound signal will be available at the collector of Q1 and it coupled to the emitter of transistor Q2 through the capacitor C4 and 1mH inductor L1. Capacitor C4 decouples the DC component from the preamplifier output. Q2 performs the job of oscillator and modulator. Inductor L2 and variable capacitor C5 forms the tank circuit necessary for creating oscillations. Capacitor C6 is the feedback capacitor. The modulated FM wave will be available at the collector of Q1 and it is transmitted using the antenna A1.
Circuit diagram.
Notes.
- Assembling the circuit on a good PCB will give better results.
- I used a 12V battery for powering the circuit. A 9V PP3 battery will also do the job.
- A battery eliminator is also fine but it will induce noise.
- Antenna A1 can be a 25cm long copper wire.
- K1 is a condenser microphone.
- C2 should be a Tantalum capacitor.
- Variable capacitor C5 can be used to adjust the transmission frequency.
- This simplified formula will help you in making inductors, L = (d²n²) / (18d+40l). Where L is the inductance of the coil in uH , d is the coil diameter in inches, l is the coil length in inches and n is the number of turns. Just try to make the inductor your self using this formaula. If you can’t, then comment here.I will give you the winding details.
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There is no specific volt identified for the capacitors. I don’t understand capacitors of which volt i’ll use for making a FM transmitter. Please help me……
There is no specific volt identified for the capacitors. I don’t understand capacitors of which volt i’ll use for making a FM transmitter. Please help me.
Sir, I’m not able to make the inductors ………. can please tell me the exact no. of turns and the diameter of the inductors, especially of the 1mH one!
Thank you.
Hi Mike Q1 is the audio amplifier. Q2 is the colpitts oscillator and the oscillator is modulated at the emitter(Q2)with audio and with the passive tank circuit the modulated RF signal is radiated.
Thanks Seetharaman It’s a good idea but I’ve another question. Can you explain me why “Q2 performs the job of oscillator and modulator”? I thought that tank circuit is oscillator but Q1 is amplifire so how transistor can create oscillations?
Hi Atul 3.9, 5.6 PF can be used here.
Hi Mike you can add a 22PF fixed capacitor in parallel with the existing C5.
I’d like to have a tramsmitter with a range about 100MHz so may I use 10-30pF variable capacitor to get lower frequencies?
plz suggest me anthr capacitor instead of 4.7pf feedback capacitor of T2.
Hi Meleja yes with C5 you can set the frequency.
How is the frequency set? Is it set via C5?
Hi Meleja between 150 and 300MHz.
Hi, what frequency does this work at?
Thanks
How find the length of a copper wire by using its weight and diameter…?
Hi Gustav if it is readily available please use it. no need to test your patience in winding.
please tell me the winding detials.
Can I use inductors bought in a an electronic shop or do I have to make it at home?
dear,send many circuits diagram for project related
what is the output frequency
Pls send the details of L in the circuit the winding detail
And antenna details
Thanks
how do i calculate the frequency? i constructed it and it worked but i need to know how to calculate the frequency.
can i change the value of variable capacitor and inductor to increase the range of frequency
please send me IR transmitter and receiver
i would like to ask is air core inductor a compulsory components? can i use other type of inductor such as coloured-band inductor? i assembled this circuit and i didnt get any output from it. can anyone tell me how to troubleshoot the circuit?
Pls. send me the winding details of the antenna for the 200M FM transmitter.
i need project on fm transmitter having frequency 500Mhz
Winding details:http://www.circuitstoday.com/how-to-make-an-air-core-inductor
You can find requency by frequency counter device
Or use the formula
F = 1 / 2π √ L X C
please tell coil turns details
Please help me to get the details of winding of inductance coil of .1uH and 1mH.
Hi Tyler diode is decoupling audio and rf stage to minimise cross modulation. C8 is the supply decoupling capacitor it can be upto 100nF.
What is the purpose of the diode, and c8 in this circuit diagram. I just finished building it and it works great!
What is the purpose of the diode? Also what is actually doing the modulating here? I just built it and it works great!!!
can you give printed circuit board (pcb) of this circuit? it is very urgent.
here what friquancy
how to calculate transmitter frequency
Hi Met you can use one of the following PCBs
http://www.aaroncake.net/circuits/fmtrans.asp
http://www.talkingelectronics.com/projects/Voyager/Voyager-P1.html
can you give this circuit’s board design? please.
(can it be 1,65 * 1,25 inches?)
Hi Saad with the given inductor and variable capacitor it will tune between 160 and 300MHz.
F = 1 / 2π √ L X C
operating frequency?
hi,how to make the inductor.wouldn’t the inductor will be available in the market,plz reply quickly,
even i hav the same doubts whch these ppl hav., hw 2 find the freq. of tranmitter? tel me much about designin of inductors.,.
ya…. its very interesting.. but at wat frequency i can receive my message..
sir tell me about how many turns required for 1mH & 0.1uH Intductors for 200m fm Transmitteralso about the thickness of wire plssss its very urgent………….plsssss ?????????????????????????????
sir can i make that inductor L3 by my own pls suggest….
What is the frequency range? I assume C5 is used to alter this?
thank you . kheily khob bood.
امیدوارم موفق باشید.
@ Dinesh
Try this link – http://www.circuitstoday.com/how-to-make-an-air-core-inductor
How to create inductors?
@ Hardik
Try this link – http://www.circuitstoday.com/how-to-make-an-air-core-inductor
How to calculate the frequency of this fm transmitter and how to make inductor coil of 0.1uH please suggest some methods to make inductor coils
De 18 and 40 are they constants. How do i increase the output power of my transmitter
Could you Plz tell the o/p frequency of the transmitter.
i.e. at which frequency I could be able to get the signal in my FM Receiver.
Plz Its URGENT.
@ Suraj
Try this link
http://www.circuitstoday.com/how-to-make-an-air-core-inductor
Hi, now i’m in Cambodia , some comnponent not easy to find but i want to buy online can u tell me where to buy (website)
good one but i want that winding details….. can u please help me…..
How to calculate the frequency of this fm transmitter and how to make inductor coil of 0.1uH please suggest some methods to make inductor coils