User Guide

PAMS
Technical Documentation
NHD–4
System Overview
Page 3–10
Original 11/97
Modulating Signals
Type:
Frequency:
Purpose:
Deviation:
Data
(FSK) 10 kbps
Instructions & Information
between Base Station & Phone
8 kHz
Type:
Frequency:
Purpose:
Deviation:
Type:
Frequency:
Purpose:
Deviation:
Type:
Frequency:
Purpose:
Deviation:
5.97 kHz 6.0 kHz 6.03 kHz
SAT
To varify a constant RF
connection from BS & Phone
2 kHz
Supervisory Audio Tone
Voice
300 Hz – 3 kHz
Person – Person
communication
12 kHz
AMPS_9
ST Signalling tone
10 kHz
Off–hook, On–hook
Hook Flash, Hand–off
8 kHz
Figure 9. AMPS: Modulating signals
As figure 9 illustrates an AMPS cellular phone can have four different types of
modulation.
DATA MODULATION
The first type of modulation a cellular phone uses when communicating with a Base
Station is Data. Data from the phone includes ESN, MIN, phone number to be
dialed and home system identification. Base Station data includes registration
conformation, notification of calls to the mobile, traffic channel assignment and
commands to adjust the mobile’s power output.
The data is Frequency Shift Keyed on the RF carrier. This is one way digital one’s
and zero’s can be modulated on an analog carrier. The 10 kHz data stream is
always transmitter by its self and not in combination with any other signal when in
the AMPS mode.
Supervisory Audio Tone (SAT)
SAT is used to insure that an RF link is being maintained between the mobile and
base station. The base station will transmit its assigned SAT frequency to the
mobile phone. When the mobile receives the SAT signal it will check to see that it is
the assigned frequency and then re–transmit SAT back to the base station. If either
the base station or the mobile fails to receive SAT the call will be terminated. SAT is
added to voice so a normal voice channel will have both voice and SAT. The user
does not hear SAT tones because they are filtered out with bandpass filters that only
allow voice frequencies to pass through.
Voice
Voice is transmitted in a range of frequencies of 300 Hz to 3 kHz. Remember that
SAT is also transmitted at the same time. The nominal deviation for Voice is 2.9
kHz and the maximum deviation for Voice is 12 kHz. Combining SAT and Voice
together will give a total maximum deviation of 14 kHz that the phone should never
exceed. If a mobile phone exceeds maximum deviation it will start interfering with
calls in adjacent channels.