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WESTERN WASHINGTON COOPERATIVE INTERFERENCE COMMITTEE <br /> WWCIC ENGINEERING STANDARD #6 REV. C (02-97) <br /> FOR RADIO TRANSMITTING AND RECEIVING DEVICES AND FM BROADCAST <br /> All communications fixed transmitter installations shall employ isolators or <br /> alternative techniques meeting the same criteria to minimize spurious radiation and <br /> intermodulation products. Additional filtering may be required according to frequency <br /> and interconnect devices as listed below. As the industry progresses, superior <br /> devices may be available and installed. <br /> The following engineering standards will be observed: <br /> Transmitters in the 29.8 to 54 MHz range shall have a low pass filter, band pass filter <br /> or cavity providing a minimum of 30 dB attenuation removed 1.0 MHz from the <br /> operating frequency. <br /> Transmitters in the 66 to 88 MHz range shall have at least 25 dB of isolation followed <br /> by a band pass cavity providing at least 20 dB of attenuation 1.0 MHz removed from <br /> the operating frequency. <br /> Transmitters in the 88 to 108 MHz range operating at a power level of 350 watts or <br /> less shall have at least 25 dB of isolation followed by a band pass cavity providing at <br /> least 35 dB of attenuation 1.0 MHz from the operating frequency. <br /> Transmitters in the 88 to 108 MHz range at power levels above 350 watts shall have <br /> a band pass cavity providing at least 25 dB of attenuation 1.4 MHz from the <br /> operating frequency. <br /> Transmitters in the 130 to 225 MHz range shall have at least 50 dB of isolation <br /> followed by a low pass filter and band pass cavity with a minimum of 15 dB of <br /> attenuation 1.0 MHz removed from the operating frequency. <br /> Transmitters in the 400 to 470 MHz range shall have at least 50 dB of isolation <br /> followed by a low pass filter and band pass cavity with a minimum of 15 dB of <br /> attenuation 2.0 MHz removed from the operating frequency. <br /> Transmitters in the 806 to 990 MHz range shall have at least 50 dB of isolation <br /> followed by a low pass filter or a band pass filter with a minimum of 15 dB of <br /> attenuation 10 MHz removed from the operating frequency and 40 dB of attenuation <br /> at 20 MHz. <br /> A band pass cavity/filter or crystal filter is recommended at the input of all receivers. <br /> Its purpose is to protect against RF energy "off frequency" from mixing in a non- <br /> linear device such as the first RF amplifier in a receiver which can re-radiate causing <br /> interference. <br /> The band reject duplexer (cross notch duplexer) may not be used without the use of <br /> cavities or isolators. <br /> coot -4.19.24 <br />