User Guide

Technical Documentation
NHD–4
System Overview
PAMS
Page 3–7
Original 11/97
High frequency signals will radiate electromagnetic waves from an antenna.
Generally the higher the power the further the waves radiate. Our voice
information is at a low frequency, these frequencies will not radiate. The solution is
to put our information onto a high frequency carrier wave.
Phone
AMPS_3
Figure 3. AMPS: Voice/RF
These signals can then be radiated out an antenna and carry our information to the
receiver.
The function of placing information on a carrier wave is called MODULATION.
Carrier
Generation
800 MHz
Modulator
Audio
Amp
Transmiter
Receiver
RF
Amplifier
Demodulator
AMPS_4
Figure 4. AMPSTX/RX:
In AMPS mode information is placed on the carrier by changing the carrier’s
frequency. The modulating signal causes the carrier’s frequency to increase and
decrease. This is called Frequency Modulation (FM), and changes to the carrier
frequency are known as deviation.
The receiver picks up RF signals, amplifies them and then retrieves (Demodulates)
information from the RF carrier. Demodulating changes in RF carrier frequency
recovers the original modulating audio frequencies.