another beginer

hello everyone
i am new in this community as well as in electronics enginnering
what i want is that if any coperative person will send me some detail of fm transmitter that how it works and any he or she have some circuits of fm transmitter which was tested by him or her then i will be very great full to you
actually i want to build a transmitter whose ranges upto 1 or 2 km min
i will be very great ful to you if anyone send me the required data on my address
austin_msa@hotmail.com

What frequency band are you interested in, what information do you plan to transmit, and oh by the way where are you located?

thank you for replying on my request .
well basically i belongs to asia.
and the frequency on which we suppose to transmitt is around 88mhz to 105 mhz. and let me clear you one thing i am a student and want to build this project as my annual project so dont take it negative
i hope you will reply me with what i want
take care

Asia is a pretty big place and there are many local rules and regulations concerning RF transmitters with a range of 1-2 km. In the US, where I live, what you are proposing would be clearly illegal as it would have the ability to interfere with commercial FM bradcasts. Power levels of 500 to 1000 mW, depending on your antenna, would caertainly disrupt our neighbors FM receivers.

There are many FM transmitter circuits which can be found on the internet by doing a google search. This and other forums also have numerous examples of FM transmitter circuits. You can do a search for relevant threads. One of the problems you will have in constructing a circuit to work in this frequency range is careful layout and construction.

You did not say if you want to transmit voice, data, or something else. That choice may have an effect on the acceptable designs.

Its also quite a detailed subject with many choices. Is there no textbook you can read about it in? In mine it covers quite a few pages...chapters even.

You want a simple FM transmitter that transmits your voice over an FM radio right? just go to google and type in FM transmitter, theres lots of these circuits around. Just don't expect more than about 200 feet or so rane, depending on how crowded your FM band is, and how good your radio is, but thats about the average I got with those kinda transmitters.

hello every one
first of all i want to clear the fact that i am no longer making this project for negative purpose what i want to do is to build a transmitter which can transmitt my voice in a defined region and let me clear one thing i am a university student and want to transmitt friendly talks in the university and as far as legal and illegal matter comes i know that in my country there are some frequency band which are legal to use only for nomn commercial usage these bands i think was callesd ism bands so dont worry that i am going to use this illegally.
As far as searching is concerned i was searching for last 2 months but was unable to find the appropiate circuit what i want is that if somebody tested the circuit and its range comes upto 1 or 2 km then plz inform me on my given id.
another thing i want to ask is that if i made a transmitter then how i set the frequency or how i would know that what frequency i have opt.

plz dont demoralize me i am new in this community

There is no demoralization here, and nobody has suggested that you had a negative purpose. In fact I'm a bit offended by your characterization of our motives. Since you are new, we just want to make sure you don't stumble into something you are not aware of. If people can broadcast on the 88 to 105 MHz band in your country it is fine by me.

There are several ways to set the frequency of your transmitter. You can use a crystal oscillator, or you can use a frequency synthesizer, or you can use a voltage controlled oscillator. There may be other ways, but those are the main ones. You can monitor your output with an oscilliscope, or a frequency counter, or a calibrated receiver.

As I mentioned in my earlier post you need a power level of 500 to 1000 mW. If you can find a circuit that will go 200 feet, and then feed that signal to an RF power amplifier, you should have what you need. In this frequency range you will need careful layout and construction technique. Keep all component leads as short as possible. As a student at the university you should have access to all kinds of test equipment.

Good Luck

thank you.
well want i want to ask is that i have attached the circuit what i planed to make but the problem is that i dont fined any place from where i can change the frequency .another thin is that it requires a 30 feet high antene to transmitt but you it is not possible to do this manually so what you advise me to do and last thing what is balun how it works and what it is

plz reply

MSA said:

thank you.
well want i want to ask is that i have attached the circuit what i planed to make but the problem is that i dont fined any place from where i can change the frequency .another thin is that it requires a 30 feet high antene to transmitt but you it is not possible to do this manually so what you advise me to do and last thing what is balun how it works and what it is

Click to expand...

This is an expanded crude 'bug' transmitter, the frequency is set (mainly) by L1 and C4, plus stray capacitance and inductance. All the other coils really need to be tuned to the same frequency as well for maximum output. Basically it's an LC oscillator, followed by a buffer, then two amplifier stages.

A balun is a "balanced to unbalanced transformer", in this case it's used to transform the 75 ohm output of the transmitter to the 300 ohm impedance of the folded dipole. You could connect a 75 ohm non-folded dipole, or 1/4 wave whip without using the balun.

I don't suppose that you have component values for the components in the picture do you?

Hi MSA, If you are trying to find a 2 km good fm transmitter,check on this site "Audio Guru FM Transmitter"....I have tried it and it is working good.......

Hi MSA,
The circuit you attached looks very powerful.
It has nothing to hold an accurate RF frequency so its frequency will drift with changes in temperature and supply voltage.
It also doesn't have pre-emphasis (treble boost) that all FM stations have so its reception will sound muffled like an AM radio or like your stereo with its treble control turned all the way down.

My FM transmitter works very well and has a range of about 2km line-of-sight.