Roofing Filter Design

Mcf or discrete crystal construction width.

Roofing filter design.

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. The amplifier provides enough gain to override the filter insertion loss. There are two basic designs for modern radios.

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. First filter as close to the antenna as possible 1 st if typical why. 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.

These allow a much better filtering curve than a roofing filter which often uses a high first if above 40 mhz. 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. 250 hz 500 hz or 1 8 khz for ssb would be acceptable values. Roofing filters are usually crystal or ceramic filter types.

To the left is the 2x 4 pole ssb filter to the right is the 2x 3 pole cw filter. 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. 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.

It is usually placed as clos e to the first mixer as possible in order to be effective. Sized to pass the widest mode of operation improve dr3 begins with. To reduce the amount of rain falling on the roof a more narrow roofing filter is required.