how to calculate the exact frequency of this FM transmitter?

so is it possible to build a small talkie walkie similar a bit to the one used in the racing world ?

No in your country you are not permitted.

what about the toys i guess it's very low frequency

You guess wrong.

doesn't cover much more than 20meters or something

Range is not a consideration for most countries, as yours and mine, it is the act of making and using an unlicensed transmitter. Again there are bands for type approved equipment and that includes toys.

Grumpy_Mike: Because some one who does not know what they are doing can cause havoc interfering with vital communications of the Police and Military. Governments do not need that extra hassle. If you do know what you are doing you can apply for type approval which means your design is independently tested to make sure there is no interference outside the band you are using and that it is being manufactured in a professional way. Of course you pay for that. If you want to learn then there is always the Amateur or Ham license but there are restrictions on the use you can put to that.

RC airplanes use a specific band and the equipment has to be type approved. Imagine you were flying your plane and it was brought down by someone messing about with an FM transmitter. You would not be pleased and it could kill someone.

aha ok your right ok i have a question which i didn't get the answer i am looking for which is : how to define the frequency i want to work on ? is it by making calculations and defining what cap, resistors and inductors i must use or .. ? and still didn't get how a walkie talkie can't interfere with another walkie talkie or even other devices ? well so far i know there is some sort of encryption, so how is that done ? and what components ?

i remember when i was a kid i got a walkie talkie for about 10$ but extremely powerful according to a toy, it was very similar to the old big real ones and can cover a very big distance, + we used to hear people talking sometimes but very few moments that this happened !

how to define the frequency i want to work on ?

It depends on the frequency range you are working in.

is it by making calculations and defining what cap, resistors and inductors

For low frequencies say less than 30MHz you can do this although the value of all these components will change with temperature with careful design you can keep it down to manageable proportions. For higher frequencies it is more complex and a simple free running oscillator will not be stable enough. There are different techniques like heterodyning, crystal oscillators and mixers, and the use of phase locked loops to name but three techniques.

Grumpy_Mike:

how to define the frequency i want to work on ?

It depends on the frequency range you are working in.

is it by making calculations and defining what cap, resistors and inductors

For low frequencies say less than 30MHz you can do this although the value of all these components will change with temperature with careful design you can keep it down to manageable proportions. For higher frequencies it is more complex and a simple free running oscillator will not be stable enough. There are different techniques like heterodyning, crystal oscillators and mixers, and the use of phase locked loops to name but three techniques.

alright instead of a simple oscillator made of conductor and 60pf, it is more efficient to use the crystal oscillators for example

Well one saving grace is that most FM receivers utilize AFC (automatic frequency control) to lock the receiver's frequency to the transmitters signal actual frequency over a given (small) capture range, so the frequency transmitted doesn't have to be exactly on the standardized channel frequency.

You don't see many building these simple FM transmitter circuits much anymore. They are of very questionable quality, drift bad, distortion is pretty high and most beginners never get them to work. If you need the functionality rather then the project experience you might consider something like this pre-made with digital frequency control.

http://www.ebay.com/itm/Naztech-N3030-Hi-Fi-Digital-Universal-FM-Transmitter-/251416114395?pt=US_FM_Transmitters&hash=item3a899174db

it is more efficient to use the crystal oscillators for example

Not efficient but stable. You have to modulate it so one way with FM is to start with an 8MHz crystal, frequency modulate it and multiply it up to the FM band.

Grumpy_Mike: You have to modulate it so one way with FM is to start with an 8MHz crystal, frequency modulate it and multiply it up to the FM band.

well i don't really understand what you mean by multiply it up to the FM band, seems a bit advanced thing

retrolefty: If you need the functionality rather then the project experience you might consider something like this pre-made with digital frequency control.

http://www.ebay.com/itm/Naztech-N3030-Hi-Fi-Digital-Universal-FM-Transmitter-/251416114395?pt=US_FM_Transmitters&hash=item3a899174db

it's about the project and learning, if i wanted to just buy then i won't be on this forum :S

i don't really understand what you mean by multiply it up to the FM band, seems a bit advanced thing

It is one of the more simple aspect to radio communications.

http://books.google.co.uk/books?id=9X5gy_mDamsC&pg=PA143&lpg=PA143&dq=radio+frequency+doubling&source=bl&ots=6oOUSS3N4_&sig=OvKvjZzDcF56rZ4Nez-2AL88lLw&hl=en&sa=X&ei=4l3YUvvnLdOO7QaE9YHwDA&ved=0CEsQ6AEwAzgU#v=onepage&q=radio%20frequency%20doubling&f=false

firashelou:

retrolefty: If you need the functionality rather then the project experience you might consider something like this pre-made with digital frequency control.

http://www.ebay.com/itm/Naztech-N3030-Hi-Fi-Digital-Universal-FM-Transmitter-/251416114395?pt=US_FM_Transmitters&hash=item3a899174db

it's about the project and learning, if i wanted to just buy then i won't be on this forum :S

Understood, it's a valid learning experiance. Just be aware that very few people successfully get those simple analog FM transmitter circuits to function at all, let alone to function well. There are ICs that include phase lock loop to generate the FM carrier frequency from a single low frequency crystal.

You might want to look at another persons analog FM transmitter circuit design. The Elliott site has many great projects ideas:

http://sound.westhost.com/project54.htm

firashelou: i don't really understand what you mean by multiply it up to the FM band, seems a bit advanced thing

firashelou: it's about the project and learning, if i wanted to just buy then i won't be on this forum :S

I'm not trying to be condescending, I genuinely have the best of intentions here, but I think this project is well over your head. RF isn't beginner material -- even folks that understand it think it's half science and half black magic. If you want to learn something new, you should probably weigh your expectations against your experience level and pick a project that is beyond your current understanding, but only a by a little -- a gap you can realistically close. OTOH, if RF is really something you're passionate about, you probably need to pick up a book on theory, and read that (and related material) until you feel like you have a solid grasp on the concept.

I see a lot of people come through here asking for advice on topics that are obviously leagues beyond their capabilities. It's a bitter pill to swallow sometimes, but providing answers to those questions is about as helpful as speaking in a foreign tongue. If the poor chap were close enough to understanding that a forum post would clear things up, they probably would've figured it out on their own.

Just my two cents...

I think the OP may be a bit confused re what is needed. A few posts back, the OP indicated they wanted to make a walkie talkie. Firstly, such radios dont operate in the FM band, but usually in the 433 - 434 UHF band , similar to UHF CB radios. Such radios use narrow band FM , bandwidth limited to a 10 Khz channel, with typically 5 Khz deviation. In this case its essential that the frequency stability of the both the transmitter and receiver is controlled by a crystal oscillator which usually provides the clock for a fractional N dual modulus pre scaling synthesiser. In my work life I used to design and make such things, and its not that hard to do , but sure isnt a beginners project. Heres a bit of an article on how such devices work. Its a bit old , and there are far better ICs around now , but the explanation is easy to understand. http://epic.mcmaster.ca/~elmer101/wx_synth/wx_pll.htm

Thanks everyone for your help :)

SirNickity: I'm not trying to be condescending, I genuinely have the best of intentions here, but I think this project is well over your head. RF isn't beginner material -- even folks that understand it think it's half science and half black magic. If you want to learn something new, you should probably weigh your expectations against your experience level and pick a project that is beyond your current understanding, but only a by a little -- a gap you can realistically close. OTOH, if RF is really something you're passionate about, you probably need to pick up a book on theory, and read that (and related material) until you feel like you have a solid grasp on the concept.

I see a lot of people come through here asking for advice on topics that are obviously leagues beyond their capabilities. It's a bitter pill to swallow sometimes, but providing answers to those questions is about as helpful as speaking in a foreign tongue. If the poor chap were close enough to understanding that a forum post would clear things up, they probably would've figured it out on their own.

Just my two cents...

SirNickity well yes your totally right, but i did read some theories and i have an idea about but i am sure i have missed a big step but i am not sure which one because when it comes to practical things, it's a mess and i feel totally confused any suggestion of what i must really look for ?

mauried: I think the OP may be a bit confused re what is needed. A few posts back, the OP indicated they wanted to make a walkie talkie. Firstly, such radios dont operate in the FM band, but usually in the 433 - 434 UHF band , similar to UHF CB radios. Such radios use narrow band FM , bandwidth limited to a 10 Khz channel, with typically 5 Khz deviation. In this case its essential that the frequency stability of the both the transmitter and receiver is controlled by a crystal oscillator which usually provides the clock for a fractional N dual modulus pre scaling synthesiser. In my work life I used to design and make such things, and its not that hard to do , but sure isnt a beginners project.

yes mauried it is exactly what my target is to build such a device but i didn't know from where to start i thought FM transmitter are a place to start, and then i realized that frequencies of a radio have a specific range of frequencies so around it there plenty to work with

mauried: Its a bit old , and there are far better ICs around now , but the explanation is easy to understand. http://epic.mcmaster.ca/~elmer101/wx_synth/wx_pll.htm

well it's not an easy article to understand :S i can't make a project out of it because for me it's not much clear

I suggest that you start with something simpler.

then i realized that frequencies of a radio have a specific range of frequencies so around it there plenty to work with

I think you need a lot more background in radio before tackling a transmitter. How about getting a short wave set ( or making one ) and get a feel for radio in the raw.

firashelou: SirNickity well yes your totally right, but i did read some theories and i have an idea about but i am sure i have missed a big step but i am not sure which one because when it comes to practical things, it's a mess and i feel totally confused any suggestion of what i must really look for ?

Haha.. welllll, no, because I have no clue what I'm doing with RF either. ;)

Mike's suggestion seems like a good step though. Shelve the transmitter for now. Build a kit or two, and when you're feeling more confident, maybe try and build a radio receiver from scratch. AFAIK, you don't need a license to receive radio anywhere, and you'll know if it works because you get a signal. (With a transmitter, you have to have a compatible receiver to know it worked -- which is two conditions instead of one.)

i checked about the walkie talkie seems it doesn't really need any license :D

Grumpy_Mike:

then i realized that frequencies of a radio have a specific range of frequencies so around it there plenty to work with

I think you need a lot more background in radio before tackling a transmitter. How about getting a short wave set ( or making one ) and get a feel for radio in the raw.

what do you exactly mean ? isnt the same of what i was trying to do ? do you mean a small transmitter ? and how can i know it's working ?