Appendix L Revision 4
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
L–8
L.4.1 Commissioning and Deployment
L.4.1.1 Local DPD Commissioning and Deployment
Comtech EF Data recommends the following procedure for local DPD commissioning. Though a
loop-back is created in this procedure, this does not create a loop in the user network since the
received data is intentionally prevented from leaving the modem when in local DPD mode.
Do these steps:
1. Setup the transmit configuration.
a. Use a Modulation and Coding (ModCod) scheme with slightly lower spectral efficiency
than expected to close the link.
b. Leave the DPD function OFF.
2. Turn ON the carrier. Leave the DPD function OFF.
a. Setup the receiver configuration to receive the looped-back signal.
b. Verify that the demodulator is locked.
c. Verify that the received signal level is within specifications.
d. Measure/record the Es/No.
3. Turn the DPD function to LOCAL.
a. After the demodulator has relocked, wait 30 seconds to allow the predistorter to fully
converge to the current transponder conditions.
b. Measure/record the DPD compensation.
c. Measure/record the Es/No and compare to previous result without DPD. If the DPD
compensation level is low <1.0 dB, then the Es/No improvement may be small since the
transponder is not driven deep into compression yet.
d. Enable the BER test mode.
4. Follow this flow chart to maximize spectral efficiency and optimize the uplink power:
5. Basic performance validation:
a. Measure/record the DPD compensation.
b. Measure/record the Es/No.
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