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Topic: how to calculate the exact frequency of this FM transmitter? (Read 17689 times) previous topic - next topic

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.
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

firashelou

Thanks everyone for your help :)



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 ?
Aiming for the unreachable !

firashelou

#32
Jan 17, 2014, 08:26 am Last Edit: Jan 17, 2014, 08:28 am by firashelou Reason: 1

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
Aiming for the unreachable !

firashelou


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
Aiming for the unreachable !

polymorph

Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

Grumpy_Mike

Quote
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.

SirNickity

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.)

firashelou

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

firashelou

#38
Jan 17, 2014, 11:11 pm Last Edit: Jan 17, 2014, 11:17 pm by firashelou Reason: 1

Quote
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 ?
Aiming for the unreachable !

firashelou


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


lol what do you mean by that :D ?

well these frequencies theories i never licked it since school but seems now that it's a must to like it if i want to be in the telecommunication field projects  :P
Aiming for the unreachable !

mauried

Get yourself a copy of this book.
http://www.arrl.org/arrl-handbook-2014

It explains the basic theory of Radio Comm pretty well, and has constructional articles of how to build both transmitterss and receivers.
Dont expect to learn everything in 5 minutes though.

SirNickity


Get yourself a copy of this book.
http://www.arrl.org/arrl-handbook-2014

It explains the basic theory of Radio Comm pretty well, and has constructional articles of how to build both transmitterss and receivers.

Hmm, I dunno.... those guys accidentally labeled the inductor in their logo with an "R".   :smiley-mr-green:

Grumpy_Mike


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


You need a licence to MAKE ONE it has to be type approved.

firashelou

ah right right to make one, yes your right i got an answer about using

and what did u mean by getting a short wave set ( or making one ) and get a feel for radio in the raw ?
Aiming for the unreachable !

Grumpy_Mike


and what did u mean by getting a short wave set ( or making one ) and get a feel for radio in the raw ?

A short wave radio receiver is a good introduction to radio. It will allow you to experience the various methods of modulation and show you the various sorts of signals you can receive and hence transmit one day. Basically there is AM, FM, and SSB also there are lots of things that sound like funny noises which are actually data. These can be Morse code, RTTY, SSTV ( slow scan TV), piccolo data, weather map fax and many more. There is a whole world in radio, start by googling SWL which is short for Short Wave Listener.
When you have got that under your belt you can go in to look into how to acquire an amateur radio license which is the only legal way you are permitted to make your own transmitter.
An introduction from a U.S. perspective is given here:-
http://www.dxing.com/swlintro.htm 

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