Frequency Allocation In Af Channels; Fig. 3-5 Typical Frequency Allocation In A 4 Khz Af Channel - ABB ETL600 Instruction Manual

ETL600
3.1.2.

Frequency allocation in AF channels

The frequency allocation of an AF channel is typically as depicted in
Fig. 3-5. The pilot band, typically at the upper end of the AF frequency
band, must be kept free because it is used by the PLC equipment for
an auxiliary signal called 'pilot'. The pilot serves several purposes such
as
•
frequency synchronization,
•
automatic gain control (AGC),
•
transmission of E- and M-telephone-signaling over the link,
•
embedded operation channel (EOC) of the link,
•
guard signal for the integrated teleprotection equipment NSD600.
Many possibilities exist for the frequency allocation of the services into
an AF channel due to
•
programmable speech bandwidth,
•
programmable bandwidths for AF data channels depending on the
required data rates,
•
programmable centre frequencies for AF data channels,
•
programmable pilot frequencies.
Fig. 3-6, Fig. 3-7 and Fig. 3-8 show all relevant possibilities for the
frequency allocation in 4 kHz, 3.2 kHz and 2.4 kHz AF channels,
respectively. Hatched areas indicate frequency bands which may be
occupied by other services. Any combination of services occupying the
frequency bands shown in the figure is allowed as long as these bands
do not overlap.
300
Fig. 3-5
Structure and Function
1KHW001489-EN
Speech
2000
Typical frequency allocation in a 4 kHz AF channel
Data
Data 600 Bd
100 Bd
November 2005
ABB Switzerland Ltd
Pilot
band
4000 Hz
3-7