Roofing Filter Design

Roofing filters are usually crystal or ceramic filter types.

Roofing filter design.

Roofing filter basics where. A close up of the roofing filter section of the frontend board. 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. 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. The ts 950 roofing filter mod consists of a 6 pole 4 to 5 khz wide filter followed by a high dynamic range feedback amplifier. 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. First filter as close to the antenna as possible 1 st if typical why.

The amplifier provides enough gain to override the filter insertion loss. The imd dynamic range will be improved 5 to 15 db for some signal spacings. These allow a much better filtering curve than a roofing filter which often uses a high first if above 40 mhz. Basically a roofing filter is simply the first if filter in a radio.

To the left is the 2x 4 pole ssb filter to the right is the 2x 3 pole cw filter. There are two basic designs for modern radios. 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. Mcf or discrete crystal construction width.

250 hz 500 hz or 1 8 khz for ssb would be acceptable values. Kenwood ts 950 series roofing filters. The term roofing stems from the fact that it protects the rest of the radio following it from out of the passband signals.