869.400MHz filter

[nighthutner]

Hi everybody. I am making a long range transciever based on RFM12BP, but i get serious problems, because the RFM outputs a lot of unacceptable noise on whole range from 100MHz up to 1GHz. Would somebody help me to design a bandpass filter for 869.4MHz center freq. BW is about 40kHz? The output power is about 500mW. I attach a measurement of the spectrum that outputs the RFM.