Welcome to Cocoontech, kaohao!
Getting rid of radio frequency interference (RFI) can require some trial and error experimentation. What works and what doesn't will depend on the frequency of the radio transmission, where it is being picked up by your installation, and what is demodulating the signal.
Do you know the frequency or call sign of the radio station(s) that are causing the interference (e.g. 880 kHz AM)?
In your case, since you didn't seem to have a problem before you hooked up the Omni, that suggests that the Omni is part of the problem.
This
web site from a ham radio operator has some good suggestions to try. What worked and didn't work for him might not be the same for you. So try each in turn. It might be easiest to start with the DSL filter in item #8, as that is pretty much plug and play.
Where to install the filters, caps, or chokes is also something that you might have to play with. You can try them where the phone line enters the house, but also at the connection to the Omni.
If you have more questions, we'll be glad to help.
Let us know how it works out!
