Comtech EF Data CDM-570A - Manual (Page 535)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix G Revision 2
G–17
Step Task
2 Verify that the PDS ration is within spec for the CDM-570A/AL.
3 Calculate the Allocated Bandwidth (BW) and Power Equivalent Bandwidth (PEB) for the duplex link:
• BW
Duplex Link
= Greater of (BW
Carrier 1
, BW
Carrier 2
)
• PEB
Duplex Link
= PEB
Carrier 1
+ PEB
Carrier 2
• Leased BW
Duplex Link
= Greater of (BW
Duplex Link
, PEB
Duplex Link
)
4 For an optimal link, the Leased Bandwidth and the Power Equivalent Bandwidth should be equal / nearly
equal.
5 Repeat the link budget process by selecting different Modulation and FEC, until the BW and PEB is
nearly balanced.
G.5.2 Estimate PSD Ratio
You can estimate PSD from a link budget using Downlink EIRP and Symbol Rate:
PSD = Downlink EIRP – 10 * Log (Symbol Rate)
PSD Ratio Example:
Carrier Downlink EIRP Symbol Rate Power Spectral Density
A to B 27 dBW 500 ksps -29.99 dBW/Hz
B to A 24 dBW 375 ksps -31.74 dBW/Hz
PSD Ratio (@ A) = -29.99 – (-31.74) = 1.75 dB
PSD Ratio (@ B) = -31.74 – (-29.99) = -1.75 dB