Understanding Modulation & Demodulation (UMD)

UMD: SOLD

Thank you to @Joseinnewworld
who just bought my 5 #NFTs, your appreciation means a lot to us 🤩 as the builder. #PayButton #eCash $XEC #NFTCollection #NFTCommunitys #nftcollector 1 #NFT gift for you coming soon after I get home pic.twitter.com/XDOeugAhxr
— Gaexe (@gaexe_) January 15, 2025

1. Modulation

It is the process of superimposing an audio signal on a carrier wave originating from an RF oscillator.

1.1 AM

Amplitude Modulation (AM) is a modulation where the amplitude of the carrier wave changes according to changes in the amplitude of the sound signal/information.

Illustration of Amplitude Modulation

1.2 FM

Frequency Modulation (FM) is a modulation where the frequency of the carrier wave changes according to changes in the amplitude of the sound signal/information.

Frequency Modulation Illustration

1.3 OSC frequency is determined by its Resonator

Resistance / Impedance Formula in Resonators

RL Circuit Against AC Current

RC Circuit Against AC Current

RCL Circuit Against AC Current

Information:

At the time of resonance:

XL > XC, then inductive
XL < XC, then capacitive
XL = XC, then the resistance

2. Modulation Technique

Modulation technique is a technique of mixing high frequency with low frequency, where the high frequency with a fixed amplitude produced by the oscillator section is used to change the modulation characteristics or amplitude, then the signal is modulated with a low frequency signal through a modulation transformer, if the signal is low frequency (+), then the high frequency amplitude increases and if the signal is low frequency (-), then the high frequency amplitude decreases.

For the modulation process in the transmitter system is carried out in the Pwr RF section. In order for the transmitter system to work well, a buffer is installed so that the impedance of the Pwr RF and OSC do not affect each other and the Buffer is installed between the two. In the transmitter system, the sine signal generator (FR) is the OSC.

2.1 OSC parts:

Class A amplifier
Resonator
Feedback (+)

2.2 Getting to know FM (Frequency Modulation) Receivers

This receiver operates on the 88-108 MHz frequency band. On this band the specified frequencies are spaced 200kHz apart.

FM Receiver Range

While the maximum frequency deviation is 75kHz. The block diagram of the FM receiver is almost the same as the AM receiver, only a little difference here:

AM receiver has no limiter circuit (amplitude limiter)
Different discriminators
In AM there is no Deeppasis network
For AM receivers the IF frequency is set at 455kHz while FM is set at 10.7Mhz, with the same bandwidth of 180kHz.

IF Frequency

FM Receiver Block Diagram

Information:

1. RF Amplifier
2. Mixer
3. IF amplifier
4. Limiter (limiter)
5. Discriminator
6. Deemphasis
7. Tone control
8. Final amplifier (pwr Amp)
A Local Oscillator
B. Trimmer factor
C. AGC (Automatic Gain Control) detector is slowed down
D. AFC (Automatic Frequency Control)

The block diagram above shows a mono FM receiver with a maximum signal sensitivity of 10µVolt. The MF tuning circuit and the local OSC (oscillator) are arranged by a variable capacitor. The OSC frequency can be changed from 98.7MHz to 118.7MHz, resulting in an IF frequency of 10.7MHz.

3. Demodulation

What is meant by demodulation / detection is the process of separating the sound signal from the carrier wave, and the following is an example of the circuit schematic.

Straight Radio Receiver

3.1 Definition of live radio:

It is a receiver that has a direct electromagnetic wave reception system that is detected without experiencing a frequency change (frequency converter).

3.2 Function of each block:

Antenna: captures electromagnetic waves from radio transmitters
Tuner: to select the desired broadcast
Detector: to separate sound waves from carrier waves
Power Amp: to amplify the sound signal produced by the detector.
Speaker: converts electrical waves into vibrations.

SOLD