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[SOLVED] Relation between Frequency and bit rate.

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jesuschrist

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I know the relation between bps and Hz as a formula but i can't imagine how the data is sent. Say I have a basic psk modulation and i want to send data from a satellite down to earth for tv. They allot me 50 MHz bandwidth. How do I send my data over this 50 MHz bandwidth between 12000 MHz and 12050 MHz. The question is do I send data at every hertz like 12000000000 Hz,12000000001 Hz , 12000000002 Hz and so on ?Do i have 50 million different carrier frequencies each sending a different data at different data rates(since faster the frequency faster the data rate) ?
 

Hi,

It seems you don´t know what modulation means. And it´s effect of bitrate and modulation sceme on necessary bandwidth.
--> Please read about modulation schemes
A quick internet search gave this:
There are many other (better) informations available.

Klaus
 
Hi;

I know what modulation is. But every textbook and source says there is a carrier frequency(which is only 1 frequency, not a bandwith which is a collection of frequencies). Take ASK for example if output of digital source V(d)t = 1 you send a sine wave at fc 12000000000 Hz if it is 0 you send nothing. You can decide the bit rate yourself depending on your digital source(you can send a bit every 1 milisecond, second or whatever you want except you wouldn't go below the carrier frequency.) What i wanted to know is that do i have 50 million different "fc " for 50 MHz bandwidth?
 

Hi,

If you read some documentetion, then you will know that every modulation causes bandwidth.
In the given document it is easy to see.

Klaus

added:
Picture:
PSKModul.PNG
 
Think I got it now kind of. I think everything goes on frequency spectrum. Since square wave is a kind of sine wave in fourier series. If i get a 50 MHz bandwidth I can use an appropriate frequency square wave for modulation(15 MHz maybe for second harmonic or 10 MHz square wave for 3rd harmonic at 5 f(d) ).ANd that 10 MHz decides my bit rate along with the modulation scheme I chose. Correct me if I'm wrong.
 

Hi,

you are getting closer.
Since PSK results in symmetric (doubled) bandwith than the input you can theoretically only use 25MHz of analog input signal bandwidth.
But now you have square wave with it´s harmonics....
You need to suppress all input frequencies above 25MHz.
A square wave has no 2nd harmonic, only odd harmonics. Therefore if you want to go to the third harmonic, then there is only 8Mbaud possible.
I´m no expert in data modulation, but I think the margin is too small.

Maybe there is a member that is experienced with PSK modulation ... he can give you more "realistic" informations.

If your input frequency is not properly bandwidth limited, then you will intrude in the next channel.

Klaus
 
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