Roofing Filter Design

250 hz 500 hz or 1 8 khz for ssb would be acceptable values.

Roofing filter design.

Kenwood ts 950 series roofing filters. First filter as close to the antenna as possible 1 st if typical why. The imd dynamic range will be improved 5 to 15 db for some signal spacings. There are two basic designs for modern radios.

For more demanding uses like listening to weak cw or ssb signals a roofing filter is required that gives a smaller passband appropriate to the reception mode in use. Protects following circuits from nonlinear operation due to strong out of band signals what. Basically a roofing filter is simply the first if filter in a radio. Roofing filter basics where.

Think of the roofing filter as a roof on a house the wide filter allows the dsp and hardware agc to respond to all the rain falling on the roof. Note the shield to improve the stop band beyond 100db and the small trimmers needed to align the cw filter to center exactly on 9 000000mhz. These allow a much better filtering curve than a roofing filter which often uses a high first if above 40 mhz. The term roofing stems from the fact that it protects the rest of the radio following it from out of the passband signals.

A close up of the roofing filter section of the frontend board. Roofing filters are usually crystal or ceramic filter types. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. To reduce the amount of rain falling on the roof a more narrow roofing filter is required.

Mcf or discrete crystal construction width. The amplifier provides enough gain to override the filter insertion loss. To the left is the 2x 4 pole ssb filter to the right is the 2x 3 pole cw filter.