Roofing Filter Design

There are two basic designs for modern radios.

Roofing filter design.

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. A close up of the roofing filter section of the frontend board. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. These allow a much better filtering curve than a roofing filter which often uses a high first if above 40 mhz.

To the left is the 2x 4 pole ssb filter to the right is the 2x 3 pole cw filter. Protects following circuits from nonlinear operation due to strong out of band signals what. First filter as close to the antenna as possible 1 st if typical why. 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.

250 hz 500 hz or 1 8 khz for ssb would be acceptable values. It is usually placed as clos e to the first mixer as possible in order to be effective. Roofing filter basics where. The amplifier provides enough gain to override the filter insertion loss.

Basically a roofing filter is simply the first if filter in a radio. 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. Roofing filters are usually crystal or ceramic filter types. Mcf or discrete crystal construction width.

Kenwood ts 950 series roofing filters. To reduce the amount of rain falling on the roof a more narrow roofing filter is required. 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.