In the regulatory domain you are using the frequency channels your law permits (it maybe outdated though). The falling of CCQ may be caused by many things like i.e interference, damage or moisture in the cables and connectors, etc etc
What hardware are you using, what is the distance, etc
Have you scanned the usage of channels in your city? Try to change channels at first, then if this doesn't help, provide more information about your setup
--Do you remember that guy who gave up? Neither does anybody else!