I got the book Electronics Cookbook from Oreilly and I have read the part about radio signals and modulation. Sorry if this question is convoluted.

I understand that in FM the frequency, or the number of times the wave repeats, changes and in AM the amplitude, or the power of the wave, changes.
I understand that part on paper, but I don't think I can picture the way it works in a real application.

In FM you start out with a carrier wave that repeats a certain amount of times and that tells the radio what the frequency is, like 102.3 or whatever right? Then you introduce a modulating wave to add the music.

Does that mean two waves are sent out? If not, how would a carrier wave repeat at the same rate if the audio or song would be changing by the second?

 

I got the book Electronics Cookbook from Oreilly and I have read the part about radio signals and modulation. Sorry if this question is convoluted.

I understand that in FM the frequency, or the number of times the wave repeats, changes and in AM the amplitude, or the power of the wave, changes.
I understand that part on paper, but I don't think I can picture the way it works in a real application.

In FM you start out with a carrier wave that repeats a certain amount of times and that tells the radio what the frequency is, like 102.3 or whatever right? Then you introduce a modulating wave to add the music.

Does that mean two waves are sent out? If not, how would a carrier wave repeat at the same rate if the audio or song would be changing by the second?

The trick with FM is that the audio signal causes a small shift in the frequency of the carrier wave. With no audio, it’s precisely the nominal frequency but with the ups and downs of a signal it shifts slightly. That ‘error’ is then observed at the receiver and used to reconstruct the original audio signal.

 

Thank you for the reply. So the small shift from the audio signal is not big enough to change the frequency?

 

Thank you for the reply. So the small shift from the audio signal is not big enough to change the frequency?

I suggest you reread many times post No. 2. He already answered your question.

Also you could try to understand it by reading here

 

I asked a question to clarify it. Lol no need to be mean about it.

 

To get a handle on modulation....you need to understand speech, or sound.

Sound has a complex structure. Complex means that sound has 2 or more components that work together to produce a sound.

The two components are amplitude and frequency. And both of these components vary with time.

So every sound has a duration of varying amplitude and varying frequency...................that make that particular sound.

That combination and duration is called a sound envelope. Every syllable has an envelope.

When you hear different people say the same word.......you are detecting the envelope....with your ears.

Even though the people use different amplitudes and frequencies......the sound or syllable was the envelope. It was the RATE of amplitude change and the RATE of frequency change that made the envelope. Envelope = two rates.

The information and intelligence is in the envelope. So when we modulate with sound and audio.....you modulate with envelopes.

If we modulate with data........ the modulation technics are different. The individual components have to be detected.....not just the envelope. It's binary or discreet. Not RATE.

In AM and FM sound modulation......we modulate with TWO rates.

Am modulation manufactures sidebands. The carrier is not changed. The sidebands vary with modulation. Fire an AM transmitter up.....watch the spectrum output.......now talk......what do you see?

Did the carrier change?

This is a youtube on FM.....but it compares it to AM. Maybe it will help you. I've never understood why textbooks teach the way they do.

 

Thank you for the reply. So the small shift from the audio signal is not big enough to change the frequency?

Read carefully the response -- "the audio signal causes a small shift in the frequency of the carrier wave". So, yes, it IS big enough to cause a change in the frequency. For instance, in U.S. broadcast FM (88 MHz to 108 MHz), the maximum frequency deviation is 75 kHz, or less than 0.1% of the carrier frequency.

 

The above might help.


Regards, Dana.

 

To get a handle on modulation....you need to understand speech, or sound.

Sound has a complex structure. Complex means that sound has 2 or more components that work together to produce a sound.

The two components are amplitude and frequency. And both of these components vary with time.

So every sound has a duration of varying amplitude and varying frequency...................that make that particular sound.

That combination and duration is called a sound envelope. Every syllable has an envelope.

When you hear different people say the same word.......you are detecting the envelope....with your ears.

Even though the people use different amplitudes and frequencies......the sound or syllable was the envelope. It was the RATE of amplitude change and the RATE of frequency change that made the envelope. Envelope = two rates.

The information and intelligence is in the envelope. So when we modulate with sound and audio.....you modulate with envelopes.

If we modulate with data........ the modulation technics are different. The individual components have to be detected.....not just the envelope. It's binary or discreet. Not RATE.

In AM and FM sound modulation......we modulate with TWO rates.

Am modulation manufactures sidebands. The carrier is not changed. The sidebands vary with modulation. Fire an AM transmitter up.....watch the spectrum output.......now talk......what do you see?

Did the carrier change?

This is a youtube on FM.....but it compares it to AM. Maybe it will help you. I've never understood why textbooks teach the way they do.

Thank you to all who answered. The envelope part helped the most.