Automatic Power Control Circuit and DC amplifier:

The automatic power control circuit controls the o/p power of the transmitter automatically, with the help of power o/p detector and DC amplifier.

Transmitter o/p is fed to duplexer. Carrier i/p for the phase modulator & the local oscillator frequency signal for mixer are produced by frequency synthesizer.

Transmitter o/p power is controlled by cell site and MTSO.

OR

APC:

The receiver picks up the special control signals and sends them to the APC (automatic power control) circuit which sets the transmitter output power level to one of the possible eight levels.

Due to APC, the received signal from the cell site becomes adequately strong and the interference is reduced with the other stations in the same or adjacent cells.

Duplexer:

The signal received by the antenna is isolated from the output stage of the transmitter with the help of a device called "Duplexer".

The duplexer will connect the received signal only to the cellular receiver input.

The duplexer output goes to the RF amplifier which boosts the level of input signal to a sufficient value and applies it to the first mixer.