Mocomtech CDM-570 - Manual (Page 150)

CDM-570/570L Satellite Modem with Optional IP Module Revision 4
Front Panel Operation MN/CDM570L.IOM
6–26
6.8.8 (CONFIG, RX) BUFFER
Edit the size, in bits, of the Plesiochronous/Doppler Buffer. The value is changed using
the
▲ ▼ arrow keys. The user should then press ENTER. Values of Disabled, +/- 128,
256, 512, 1024, 2048, 4096, 8192, 16384 and 32768 bits are possible.
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). This menu choice is shown below:
If the IP Module is installed and the selected Data Interface is IP, the buffer is Disabled
by default and this is the only valid selection.
When a value other than ‘Disabled’ is selected, the Plesiochronous/Doppler buffer is
enabled, and set to the selected size. This is shown below:
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 CDM-
570/570L can be operated 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).
6.8.9 (CONFIG, RX) INVERSION FUNCTIONS
Select Spectrum or Data, using the ◄ ► arrow keys, then press ENTER.
Rx Buffer: Disabled (Loop
Timing Mode)( ▲ ▼, ENTER)
Rx Buffer: +/-32768 Bits
(13.1ms) (
▲ ▼, ENTER)
Rx Inversion functions:
Spectrum Data (
◄ ►,ENT)