Roofing Filter Design

The term roofing stems from the fact that it protects the rest of the radio following it from out of the passband signals.

Roofing filter design.

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. Protects following circuits from nonlinear operation due to strong out of band signals what. 250 hz 500 hz or 1 8 khz for ssb would be acceptable values.

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

Sized to pass the widest mode of operation improve dr3 begins with. 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. Mcf or discrete crystal construction width. To reduce the amount of rain falling on the roof a more narrow roofing filter is required.

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. Basically a roofing filter is simply the first if filter in a radio. First filter as close to the antenna as possible 1 st if typical why. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping.

There are two basic designs for modern radios. It is usually placed as clos e to the first mixer as possible in order to be effective. Roofing filter basics where.