Comtech EF Data SLM-5650A User Manual
Page 350
SLM-5650A Satellite Modem
Revision 8
Appendix B
B–16
Figure B-4. Doppler Shift
If the two earth stations are configured as master/slave, then the buffer need only be configured
for Doppler operation. The buffer will then have sufficient capacity for the Doppler shift on the
outward and return paths.
A buffer set up for Doppler operation only will typically require less depth than one intended for
both Doppler and plesiochronous operation.
B.4.1
Buffer Size
The depth of the receive buffer will depend on four parameters:
1.
Doppler shift caused by satellite.
2.
Stability of each clock (plesiochronous/Doppler operation).
3.
Frame/Multiframe length of multiplexed data format.
4.
Allowable time between clock slips.
B.4.1.1 Doppler
A geostationary satellite should be positioned directly over the equator and orbit with duration of
24 hours. In practice, the exact inclination of the satellite (relative to the equator) is influenced by
the earth, moon, and sun’s gravity, as well as solar wind. Station-keeping motors are required to
maintain the orbital position.