no you dont need to use the plate
There is a
DISEQC switch in the LNBF to select
C band or Ku band.
How do you have it hooked up (cable wise)? - explain your cable connections.
You can verify Ku by removing the short coax jumper and putting your receiver cable directly into the Ku connector.
What receiver are you using? Are you using PORT 1 for C band and PORT 2 for Ku band?