Estimate Psd Ratio - Comtech EF Data CDM-570A Installation And Operation Manual

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Appendix G
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:
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 Ratio Example:
Carrier
A to B
B to A
PSD Ratio (@ A) = -29.99 – (-31.74) = 1.75 dB
PSD Ratio (@ B) = -31.74 – (-29.99) = -1.75 dB
BW = Greater of (BW
•
Duplex Link
PEB = PEB
•
Duplex Link Carrier 1
Leased BW = Greater of (BW
•
Duplex Link
PSD = Downlink EIRP – 10 * Log (Symbol Rate)
Downlink EIRP
27 dBW
24 dBW
, BW )
Carrier 1 Carrier 2
+ PEB
Carrier 2
, PEB
Duplex Link Duplex Link
Symbol Rate Power Spectral Density
500 ksps
375 ksps
G–17
MN-CDM570A
Revision 3
)
-29.99 dBW/Hz
-31.74 dBW/Hz