Doppler Buffer - Comtech EF Data SDM-650B Installation And Operation Manual

Configuration

3.3 Doppler Buffer

The Doppler buffer assembly is an option that plugs on to the modem interfaces, that
provides elastic buffering to the receive data channel. The Doppler buffer compensates
for the effect of satellite movement or disparity between transmit and receive clocks, and
can be used at data rates of 9.6 kbit/s to 2.5 Mbit/s.
Note: 120
AS/0679 PCBs.
The Doppler buffer attaches into the receive data path on the interface assembly at TTL
signal levels. The buffer should be attached before the signals are configured to the
specific interface type.
The buffer assembly is compatible with many different interface types.
The clock source for the buffer output can be selected from one of three sources:
•
•
•
If the transmit clock source is selected, the buffer output is used after being recovered and
dejittered (if necessary). Any signal with which the transmit side is designed to work can
supply a valid buffer output clock.
Jumpers on the buffer determine local clock source control, or the M&C system control.
The modem software must be configured for buffer support in order to use M&C
functions from the front panel.
To select the required buffer depth for the system, the maximum peak-to-peak
transmission delay variation has to be known.
Refer to Table 3-8 for jumper settings.
Refer to Table 3-9 for the delay variation of an INTELSAT satellite.
3–40
Ω impedance-matching resistors are required on the AS/0627, AS/0569, and
Receive channel (effective bypass mode)
Modem transmit clock
External customer supplied reference clock
SDM-650B Satellite Modem
Rev. 5