# Question about decoding information in electromagetic wave

• Jackson Lee
In summary: AM) or frequency modulation (FM) or any other types of modulationthe antenna's job is to collect the RF energy from the transmitter and to radiate it out into spacethe antenna does not care if the RF energy is modulated or notIn summary, the conversation discusses the production and decoding of electromagnetic waves by a dipole antenna. The EM waves are emitted as a torus with varying amplitudes, and the discussion touches on the use of modulation and demodulation in the transmission and reception of the waves. The conversation also mentions the influence of reflections and interference on the signal.
Jackson Lee
When electromagenetic wave is produced by dipole antenna, all the space exist EM waves like torus with different amplitude. Even though waves could reach destination, then how to decode information within it?

Jackson Lee said:
When electromagenetic wave is produced by dipole antenna, all the space exist EM waves like torus with different amplitude. Even though waves could reach destination, then how to decode information within it?

How much do you know so far about modulation and demodulation? Maybe start with this wikipedia article, and post any specific questions you have after reading that article:

https://en.wikipedia.org/wiki/Modulation

Jackson Lee
berkeman said:
How much do you know so far about modulation and demodulation? Maybe start with this wikipedia article, and post any specific questions you have after reading that article:

https://en.wikipedia.org/wiki/Modulation

I have just read the article, thanks a lot, but I'm still confused. My question is after completing modulation of the signal, when ejecting it out via dipole antenna, it will create many kinds of signal at different points in space(This is my opinion, because at different points in space there exist different electrical and magnetic magnitudes, thus at different directions in space there exist different EM waves [if it is wrong,please correct it]), then when all these signal from the same source reach same destination, how to demodulate the real meaning from others?

The signal of a specified frequency (say your 101.7MHz FM station) and a specified modulation, in this case FM, (EM) is radiated by the transmitting antenna and picked up by any antennas within range. the antenna connects to a receiver and if the receiver can tune to the 101.7 MHz frequency, it will be amplified and sent to the demodulator circuit, again, in this case an FM demodulator, where audio will be recovered

do some google searching on FM and AM modulation and demodulation and ask any specific questions of anything you don't understand
Supply links to those places so we can also read what you areDave

Jackson Lee
davenn said:
The signal of a specified frequency (say your 101.7MHz FM station) and a specified modulation, in this case FM, (EM) is radiated by the transmitting antenna and picked up by any antennas within range. the antenna connects to a receiver and if the receiver can tune to the 101.7 MHz frequency, it will be amplified and sent to the demodulator circuit, again, in this case an FM demodulator, where audio will be recovered

do some google searching on FM and AM modulation and demodulation and ask any specific questions of anything you don't understand
Supply links to those places so we can also read what you areDave
Thanks a lot, maybe I need to make my question clear. According to this[https://en.wikipedia.org/wiki/Dipole] , electric field of all the points in bisecting plane are dependent on the distance to axis. When the dipole is oscillating constantly, it seems electric field of all the points in the plane are changing with same frequency but amplitude related to distance to axis. Could all these points produce their EM waves? If so, many waves with different magnitude will reach destination if we use AM method, then how to modulate and demodulate signal? There must be wrong somewhere, but I don't know. Correct it please.

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Jackson Lee said:
When electromagenetic wave is produced by dipole antenna, all the space exist EM waves like torus with different amplitude.

Just so we're clear, the torus shape you see is a representation of the amplitude of the emitted wavefront or the gain of the antenna. The wavefront itself is NOT shaped like a torus.

Jackson Lee said:
Thanks a lot, maybe I need to make my question clear. According to this[https://en.wikipedia.org/wiki/Dipole] , electric field of all the points in bisecting plane are dependent on the distance to axis. When the dipole is oscillating constantly, it seems electric field of all the points in the plane are changing with same frequency but amplitude related to distance to axis. Could all these points produce their EM waves? If so, many waves with different magnitude will reach destination if we use AM method, then how to modulate and demodulate signal?

For the most part, only a very, very small part of the expanding wavefront will reach a receiver. You can have reflections and will have interference when the phase of these reflected parts aren't in phase with the main signal, but as long as the main signal is much larger in amplitude than the reflected parts you just demodulate it as normal. If the out of phase parts begin to approach the amplitude of the main signal then you start having problems. The amount of noise these reflected signals (or other sources of interference) also heavily depends on the type of modulation used. Amplitude modulation is notorious for being highly susceptible to noise, while FM is far less susceptible.

For the exact details on modulation and demodulation you can see the following links or search google.

https://en.wikipedia.org/wiki/Demodulation
http://web.mit.edu/6.02/www/s2012/handouts/14.pdf

Last edited by a moderator:
Jackson Lee said:
When the dipole is oscillating constantly, it seems electric field of all the points in the plane are changing with same frequency but amplitude related to distance to axis.

The dipole doesn't oscillate ... there is RF AC (RF alternating current) oscillating in the dipole. The frequency of that RF current is emitted from the dipole as a changing electromagnetic field. The EM field strength drops off in intensity calculated by the
inverse square law.

Jackson Lee said:
Could all these points produce their EM waves?

all what points ?

Jackson Lee said:
If so, many waves with different magnitude will reach destination

there is only one source of the RF energy --- the transmitting antenna

Jackson Lee said:
if we use AM method, then how to modulate and demodulate signal? There must be wrong somewhere, but I don't know. Correct it please.

as I said in my previous post...

the modulator section in the transmitter circuit does the modulating
the demodulator circuit section in the receiver does the demodulating

the antennas know nothing about the types of modulation being used

Dave

Drakkith said:
Just so we're clear, the torus shape you see is a representation of the amplitude of the emitted wavefront or the gain of the antenna. The wavefront itself is NOT shaped like a torus.
For the most part, only a very, very small part of the expanding wavefront will reach a receiver. You can have reflections and will have interference when the phase of these reflected parts aren't in phase with the main signal, but as long as the main signal is much larger in amplitude than the reflected parts you just demodulate it as normal. If the out of phase parts begin to approach the amplitude of the main signal then you start having problems. The amount of noise these reflected signals (or other sources of interference) also heavily depends on the type of modulation used. Amplitude modulation is notorious for being highly susceptible to noise, while FM is far less susceptible.

For the exact details on modulation and demodulation you can see the following links or search google.

https://en.wikipedia.org/wiki/Demodulation
http://web.mit.edu/6.02/www/s2012/handouts/14.pdf

davenn said:
The dipole doesn't oscillate ... there is RF AC (RF alternating current) oscillating in the dipole. The frequency of that RF current is emitted from the dipole as a changing electromagnetic field. The EM field strength drops off in intensity calculated by the
inverse square law.
all what points ?
there is only one source of the RF energy --- the transmitting antenna
as I said in my previous post...

the modulator section in the transmitter circuit does the modulating
the demodulator circuit section in the receiver does the demodulating

the antennas know nothing about the types of modulation being used

Dave
Thanks a lot to both of you, I got it. Your answers are fantastic(smile)

davenn

## 1. What is the process of decoding information in electromagnetic waves?

The process of decoding information in electromagnetic waves involves extracting the electromagnetic signals from a carrier wave and decoding them using a receiver. This can involve using various techniques such as amplitude modulation, frequency modulation, and phase modulation to retrieve the original information.

## 2. How do electromagnetic waves carry information?

Electromagnetic waves carry information through variations in their amplitude, frequency, or phase. By modulating these characteristics, different types of information can be encoded and transmitted through electromagnetic waves, such as radio waves, microwaves, and light waves.

## 3. What types of information can be decoded from electromagnetic waves?

A wide range of information can be decoded from electromagnetic waves, including audio signals, video signals, data signals, and digital signals. This allows for various forms of communication, such as radio and television broadcasting, wireless internet, and satellite communication.

## 4. Can the decoding process be affected by interference?

Yes, the decoding process can be affected by interference from other electromagnetic signals or external factors such as weather conditions. This can result in a loss or distortion of the information being decoded, which can affect the quality of the communication.

## 5. How is the decoded information interpreted by the receiver?

The decoded information is interpreted by the receiver based on the modulation technique used. For example, in amplitude modulation, the varying amplitude of the electromagnetic wave is translated into sound or image signals. In frequency modulation, the varying frequency is translated into different pitches or colors.

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