its a silly question ,i think but i have no way

if write a code to make 21000000(MHZ) cylcles per second and connect a antenna wire in any digital out pin.doesn't it produce radio waves.I know i am basically have bad basic knowledge. Please help me to understand what is my misunderstanding.

If you could do that, how would you prove it?
Tune a radio to that freq and watch the signal meter go back and forth (signal present/absent)?

How would you do 21 MHz?

i don't get you.explain me basically.

actually if i want to send a data 1001(9) with carrier frequency of 21MHZ(t=21um)
why dont i make mark of 20 ms(1) 10ms(0) 10ms(0) and finally 20ms(1) with space of 10ms
if i do same decoding on other side wont i get the vale

1. What you want to do is illegal.
2. How are you going to start and stop the carrier with such precision, you are not going to do it with an arduino.

A logic signal isn't sinusoidal so you'd output a whole bunch of harmonics across the
spectrum too... This is the cause of electro-magnetic interference from digital electronics
and why you specifically avoid hanging single wires off a signal.

ohhh. So ,is it the reason why Xbee and rf modules are.isn't it?

Those modules convert digital into analog signals and transmit with some modulation tecqnuice which is same as used in receiver side and it will be again decode to digital data. The transmission is in analog so no harmonics i mean noise ,am i right?

So ,is it the reason why Xbee and rf modules are.isn't it?

Yes. They use the correct frequencies and are type approved. That means the design has been submitted to testing by an approved test house.
They also know what they are doing.

The transmission is in analog so no harmonics i mean noise ,am i right?

No you are not right. All RF transmitters produce harmonics the trick is to keep them to an absolute minimum. Turning a transmitter on and off produces harmonics all over the band.

Yes. They use the correct frequencies and are type approved. That means the design has been submitted to testing by an approved test house.
They also know what they are doing.

the licence free band vary for different countries.so the xbee and rf have different working frequencies in different country

bhuvaneshnick:
the licence free band vary for different countries.so the xbee and rf have different working frequencies in different country

So what has that got to do with anything?
Bottom line constructing a transmitter without a license is illegal in just about every country.

okay.By the way i have tried ir transmission with pwm modulation to control my sony bravio tv.Then i started to think why don't we use same way to produce rf transmission.That leads me here

Then i started to think why don't we use same way to produce rf transmission.

Well, to start with, there's the length of antenna you'd need at 38kHz.

(Do the arithmetic)

1/38KHZ=26um length antenna.

Maybe you want to reconsider your arithmetic.

( the old UK long wave service is 1500 meters / 200 kHz)

this is the calculation as far as i know, thats why the AM towers are taller that FM

I don't know and can't imagine how you arrive at a tiny fraction of a millimetre as an antenna length for a 38kHz radio wave.
Put it this way, in air, a 40kHz ultrasound signal has a wavelength of over eight millimetres.

Sound travels an awful lot slower than radio.

bhuvaneshnick:
this is the calculation as far as i know, thats why the AM towers are taller that FM

As far as I'm aware, the modulation scheme has little to do with antenna length.
Frequency is an entirely different matter, however.

bhuvaneshnick:
1/38KHZ=26um length antenna.

So you take the reciprocal of frequency and you get length!
Maths doesn't work like that. What you have calculated is the period of the wave in mS.

Wavelength = C / F
Where F is the frequency and C is the speed of light.

bhuvaneshnick:
Yours for the making - Instructables