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CDM-Qx Satellite Modem
Front Panel Operation
(Config%Rx%Buf) – RX BUFFER CLOCK SOURCE
Rx Buffer: Internal Rx-Sat
Tx-Terr Ins External (◄ ►, ENT)
The user will select which Rx buffer clock source. Note that Tx-Terrestrial will only be
selected if the cards are grouped as modem. Selecting either one will allow the user to
select the buffer size as shown below (also, note that External will only be selected if
QDI interface type is selected):
Rx Buffer Size:
Disabled
Values of Disabled, ± 512, 1024, 2048, 4096, 8192, and 16384 bits are possible. Edit
the size, in bits, of the Plesiochronous/Doppler Buffer. The value is changed using the #
$ arrow keys, then pressing
Note: For QDI interface type, the selectable Rx Buffer settings are Rx-Sat, Tx_Terr and
External:
When Disabled is selected, the Plesiochronous/Doppler buffer is disabled. The receive
clock will then be derived from the satellite signal, and will therefore be subject to clock
offsets relative to the local transmit clock, This is due in part to the originating clock
being slightly different from the local clock (a so-called plesiochronous offset), and to
the motion of the satellite (a Doppler offset).
The input to the buffer will be the signal from the satellite, with any clock offsets and
jitter. The output from the buffer will be derived from the local TRANSMIT clock. In
this way, the receive data will be perfectly synchronous with this local clock.
The modem operates with independent receive and transmit data rates. Even in this
configuration, where RX data rate <> TX data rate, the output clock for the buffer will be
phase locked to the transmit clock.
While it is only possible to select the size in bits, the corresponding total buffer size is
displayed in ms (which will vary in inverse proportion to the data rate).
(▲ ▼, ENT)
ENTER
•
Tx-Terr is a recovered E1 clock from the Tx terrestrial E1 data. This setting
will also loop the Tx terrestrial E1 data to the Rx terrestrial E1 data port. The
incoming Rx IF data will be instered and overwrite this "looped" data.
•
External is a user-provided E1 frequency balanced clock on J5 of the Quad
E1 interface card.
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Revision 6
MN/CDMQx.IOM
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