Roofing Filter Design

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

Roofing filter design.

There are two basic designs for modern radios. Basically a roofing filter is simply the first if filter in a radio. The imd dynamic range will be improved 5 to 15 db for some signal spacings. Roofing filters are usually crystal or ceramic filter types.

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. Roofing filter basics where. A close up of the roofing filter section of the frontend board. 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. It is usually placed as clos e to the first mixer as possible in order to be effective. 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.

To the left is the 2x 4 pole ssb filter to the right is the 2x 3 pole cw filter. The term roofing stems from the fact that it protects the rest of the radio following it from out of the passband signals. Mcf or discrete crystal construction width. 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.

Sized to pass the widest mode of operation improve dr3 begins with. The amplifier provides enough gain to override the filter insertion loss. Protects following circuits from nonlinear operation due to strong out of band signals what.