Understanding AM and FM Radio Signals: BLV, DBL, and BLU Modulation

A carrier signal is transmitted along with a full sideband.
To reduce reception costs, a portion of the other sideband, near the carrier, is removed. This is referred to as a “trace.”
Increases the number of channels per band (n1) and performs better than standard AM.
Suitable for large-scale communications.

The power transfer is concentrated solely in the sidebands, resulting in a 50% yield.
Demodulation is straightforward, although it requires additional, more expensive circuitry.
This modulation is used when reducing transmitter power is desired or when the carrier might interfere with other signals.
Applicable in scenarios with multiple signal transmitters.

To improve transmitter performance, both the carrier and one of the sidebands can be eliminated.
All the transmitted power is useful, as only the entropy of the original message is sent, achieving a 100% return in the transmitter.
The spectrum is reduced by half, potentially increasing the number of channels used.
Due to spectrum reduction, the receiver becomes significantly more complex than the conventional version.
Requires specialized and expensive receivers. Consequently, its usage is limited to applications that can justify the higher cost.
Not used for large-scale broadcasts because it is more cost-effective to have simpler receivers.

Block Diagram of an AM/FM Receiver

Here’s a breakdown of the components and their functions:

Antenna: Converts electromagnetic waves into electrical current.
Tuning Circuit: Selects the desired station and filters radio frequency signals.
Converter: Changes the carrier frequency, lowering it to 10.7 MHz. This is known as the intermediate frequency (IF) signal. Using a fixed IF simplifies filtering and improves performance.
Intermediate Frequency Amplifier: Amplifies the IF signal while rejecting unwanted frequencies using highly selective bandpass filters. In FM, the filter allows a bandwidth of +100 kHz to accommodate the 10.7 MHz IF. In AM, the bandpass filter is centered at 455 kHz.
Demodulator (AM or FM): Extracts the audio signal from the carrier. The FM demodulator processes a stereo multiplex signal, which is then sent to the stereo decoder. The AM demodulator extracts the audio signal, which is typically sent to both speakers in mono.
Stereo Decoder: In FM, this circuit separates the multiplex signal into left and right channel audio signals.
Automatic Sensitivity Control: Implemented in the AM receiver, this circuit adjusts the sensitivity. If the signal is strong, it instructs the IF amplifier to reduce amplification. Conversely, if the signal is weak, it increases amplification.

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