# Arduino Forum

## Using Arduino => General Electronics => Topic started by: firashelou on Jan 16, 2014, 10:14 am

Title: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:14 am
hello guys,
i have a schematic of FM transmitter so i build it on breadboard but i got some components that are different from the schematic, so i guess this changes the frequency which should be 102.3 MHZ, in fact this frequency in my country is used (can i still be using it and interfere to the station that is using it ?)
so i need to calculate the new frequency which i should check to hear the sound from my transmitter, how can i do that ?

the original schematic in attachment file

my changes are :
instead of R5 47K i used 50K
instead of 4.7uF i used 2.2uF
instead of of 220K i used 200K
instead of variable capacitor C5 i used a ceramic 0.1uF
instead of the inductor used i put a piece of wire and made it into a coil
as an antenna i used a piece of wire about 17cm attached to the + of the inductor

i assume there is connection between R2, R3 and the base of transmitter is that right ?
and a connection between the LED, 330ohm and the base ot the second transmitter ?

Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: mauried on Jan 16, 2014, 01:00 pm
What are you trying to do with this transmitter?
The frequency is given by the formula 1 / 2 X pi X sqroot (L X C), but as
the circuit has the oscillator as the output stage , its frequency stability will be terrible.
You need some kind of crystal oscillator followed by a multiplier to get a stable frequency.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: MarkT on Jan 16, 2014, 01:21 pm
Nice thought, but you really don't want a stable frequency for wideband FM, you
have to shift the frequency +/-200kHz or so according to the modulation input,
0.1% or so, far more than a crystal can be "bent".   _Narrowband_ FM can be done
with crystals (deviation is more like 2.5kHz), wideband you need either PLL or DDS
techniques or an modulated LC oscillator like this.

The frequency is set by the tank circuit, C6/L1, since C6 is a trimmer anyway that
should give a wide range of adjustment.

Without a spectrum analyser you'll have to use a radio receiver to tune this
transmitter.

Note that this circuit is primitive and the antenna will affect the tuning so you must
tune with the antenna you will be using.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: michael_x on Jan 16, 2014, 01:57 pm
Quote
instead of the inductor used i put a piece of wire and made it into a coil

Hopefully you manage to hit a frequency in the range of your radio receiver (88 .. 108 MHz is not a too broad range).

Quote
Note that this circuit is primitive ...
... so chances are good the mic audio signal affects frequency somehow and produces an FM-like signal. I guess if it works at all, it will affect all FM radio frequencies. No need to worry about 101.3 in special. ;)
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 16, 2014, 04:19 pm
So you used a 100,000pF ceramic capacitor in place of a 6 to 60pF variable? So I'd say the frequency is 0Hz, because it won't oscillate.

As for the coil, there is no way anyone can tell you the inductance with the information you gave.

This is a rather unstable oscillator, for the reasons given. Pretty much anything you change that is connected to Q2 (including the battery condition) will change the frequency. You can get close by calculating the resonance of C5 and L1, although the frequency will be something lower than that due to the feedback capacitor C6 and the transistor's operating point characteristics.

So the only way to know for sure is either tune a radio into its signal, or use a frequency counter. If you connect an oscilloscope probe or anything else directly to it, you'll lower the frequency.

What a horrid schematic. Terrible place to draw a (wasteful) power LED. And the LED is pointing the wrong way.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: MarkT on Jan 16, 2014, 04:32 pm

What are you trying to do with this transmitter?
The frequency is given by the formula 1 / 2 X pi X sqroot (L X C), but as
the circuit has the oscillator as the output stage , its frequency stability will be terrible.
You need some kind of crystal oscillator followed by a multiplier to get a stable frequency.

Actually it may more complex than you think, since its a modified Hartley
oscillator several capacitors are contributing to the overall capacitance.
(Including those of the device itself which are modulated by the input)

Tuning a radio into the output is a fairly sane way to tune this (although
it will also detect harmonics, so a rough calculation based on the component
values is a good safety check.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 16, 2014, 05:24 pm
Like 100,000pf for the resonating capacitor? ;')
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 05:33 pm

Like 100,000pf for the resonating capacitor? ;')

well yea i thought this will affect it big time, i just used because i didn't have the 60pF trimmer but seems it's very wrong !

about the tuning using a radio, what do you mean by that ?

about the inductor, it's 6 rounds, 0.5 cm diameter
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 16, 2014, 06:07 pm
Well, it is only about 2000x larger. :'/ What happens if I put mining truck tires on my car? It isn't meaningful any more to ask how fast it can go, because it won't work.

Tuning the radio? I meant tuning your receiver around until you hear the signal from the transmitter.

We need to know a lot more about the inductor to calculate the inductance. Is that 5mm inner or outer diameter? How long is it? Wire gauge?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 06:31 pm
Quote
in fact this frequency in my country is used (can i still be using it and interfere to the station that is using it ?)

Most countries will not allow you to transmit in this band anyway.
If you fill in the location information in your profile everyone can see it and give you better advice.

In general this is a broadcast band and using any frequency is illegal especially using such an unstable circuit.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 08:18 pm

Well, it is only about 2000x larger. :'/ What happens if I put mining truck tires on my car? It isn't meaningful any more to ask how fast it can go, because it won't work.

Tuning the radio? I meant tuning your receiver around until you hear the signal from the transmitter.

We need to know a lot more about the inductor to calculate the inductance. Is that 5mm inner or outer diameter? How long is it? Wire gauge?

i guess it's better to buy an inductor than build one like that
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 08:19 pm

Quote
in fact this frequency in my country is used (can i still be using it and interfere to the station that is using it ?)

Most countries will not allow you to transmit in this band anyway.
If you fill in the location information in your profile everyone can see it and give you better advice.

In general this is a broadcast band and using any frequency is illegal especially using such an unstable circuit.

than what is the solution ? how can i choose a specific frequency and make a circuit for that frequency ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 16, 2014, 09:50 pm
First, tell us what you are trying to accomplish.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:06 pm

First, tell us what you are trying to accomplish.

ok my goal is to go from here to build a system like the walkie talkie or something small similar to the communication system used in racing when the team speak to driver and the driver speak back

i can say after i finished the book i was reading i managed to build a small speaker system, and i can say i have an idea (not very advanced but i am not much confused like when i first started) of what is going on in sound stuff
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 10:10 pm
From the document attached:-
Quote
Article 14: Requirement of a Frequency License
1. Subject to Article 14 (3), no Person may use Radio Frequencies or operate a radio apparatus in Lebanon, or on board of any ship, aircraft or space object that is registered in Lebanon, unless authorized by a Frequency License of the Authority.

See the last section of the document for:-

I don't think they will allow you to make a transmitter to do this. Also see "type approved in Lebanon".
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:27 pm

I don't think they will allow you to make a transmitter to do this. Also see "type approved in Lebanon".

but why what is the reason, if it is just like the FPV used on RC airplanes ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 16, 2014, 10:30 pm
Because that radio is carefully designed by trained engineers, extensively tested, and approved.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:34 pm

Because that radio is carefully designed by trained engineers, extensively tested, and approved.

so is it possible to build a small talkie walkie similar a bit to the one used in the racing world ?
and what about the toys i guess it's very low frequency that doesn't cover much more than 20meters or something ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 10:38 pm

but why what is the reason, if it is just like the FPV used on RC airplanes ?

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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 10:41 pm
Quote
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.

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

You guess wrong.

Quote
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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:46 pm

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.

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 !
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 10:53 pm
Quote
how to define the frequency i want to work on ?

It depends on the frequency range you are working in.
Quote
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.

Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 10:56 pm

Quote
how to define the frequency i want to work on ?

It depends on the frequency range you are working in.
Quote
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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: retrolefty on Jan 16, 2014, 10:58 pm
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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 11:01 pm
Quote
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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 11:18 pm

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 16, 2014, 11:20 pm

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 16, 2014, 11:26 pm
Quote
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.

Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: retrolefty on Jan 16, 2014, 11:29 pm

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: SirNickity on Jan 17, 2014, 02:08 am
i don't really understand what you mean by multiply it up to the FM band, seems a bit advanced thing

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...
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: mauried on Jan 17, 2014, 07:38 am
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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 08:24 am
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 ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 08:26 am

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 09:09 am

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: polymorph on Jan 17, 2014, 02:47 pm
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 17, 2014, 04:53 pm
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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: SirNickity on Jan 17, 2014, 10:04 pm
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.)
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 11:10 pm
i checked about the walkie talkie seems it doesn't really need any license :D
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 11:11 pm

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 ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 17, 2014, 11:15 pm

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
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: mauried on Jan 17, 2014, 11:17 pm
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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: SirNickity on Jan 18, 2014, 12:38 am

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:
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 18, 2014, 12:52 am

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.
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 18, 2014, 01:03 am

and what did u mean by getting a short wave set ( or making one ) and get a feel for radio in the raw ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: Grumpy_Mike on Jan 18, 2014, 08:22 am

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 (http://www.dxing.com/swlintro.htm)
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 18, 2014, 08:03 pm

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.

i found the 2013 version of this book, it should be mostly the same as 2014 ?
Title: Re: how to calculate the exact frequency of this FM transmitter?
Post by: firashelou on Jan 18, 2014, 08:04 pm

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 (http://www.dxing.com/swlintro.htm)

aha ok Grumpy Mike this should be a good start thanks :)