Attenuatation won't get rid of the interference completely. Try a 1/4 wave stub in series with your coax line. A 1/4 wave stub can be made by using a BNC T connector in-line with your coax at the radio end. Join one end of the T connector to the radio and the other end to the antenna. Then connect a length of coax to the free end of the T connector. Cut the length of the coax slightly longer than the 1/4 wave length of the interfering frequency i.e. 460.375 = 0.163meters.
Then tune the radio to that frequency and start to cut down the length of coax in small sections and watch the signal strength meter. (better resolution is achieved if you add attenuation) You should see the signal strength start to reduce in level. When it seems that the signal strength has reached its weakest level, stop cutting.
This is a cost effective way of notch filtering. The better the coax you use, the better the Q of the attenuation.
Good luck
Michael
