Comtech EF Data MIDAS Version 4.X Basic Configuration User Manual
Page 93
MIDAS 4.2 Basic Configuration, Rev. 1
Setup and Operation 2–59
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Use this drop-down list to select the Forward Error Correction (FEC) rate for
the traffic modem, either 5/16, 21/44, 1/2, 3/4, 2/3, 5/6, 7/8, 8/9, or 1/1
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Select a data rate for the traffic modem.
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Using the drop-down box allows the user to select the Encoding type, Viterbi,
Sequential, Turbo, TCM, TCM with Reed-Solomon, Viterbi with Reed-
Solomon, or Sequential with Reed-Solomon.
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Enter the Doppler Buffer size, in bits, to compensate for satellite movement.
The depth of the receive buffer will depend upon four parameters:
• Doppler shift caused by satellite movement
• Stability of each clock (plesiochronous/Doppler operation only)
• Frame/Multiframe length of multiplexed data format
• Allowable time between clock slips
Doppler shift results from the movement of the satellite in space over a period
of one day in relation to the earth station. Doppler shift should not result in a
clock slip as the buffer will constantly fill and empty due to the cyclic nature of
the satellite motion.
Depending on the location of the earth station relative to the satellite, the
variation in propagation delay will typically be 1.15 ms (up to satellite and
back down). So, 2 ms will be sufficient for most commercial satellites.
Bits to Seconds:
1/DATA RATE * BITS = SECONDS
Seconds to Bits:
DATA RATE * SECONDS = BITS
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The DVB Frame field is displayed in the Communication Settings window
ONLY when an SDM-2020 is selected. Valid entries are 187, 188, and 204.