How To Use Roofing Filters

There are two basic designs for modern radios.

How to use roofing filters.

If your family has health or allergy issues then you may want to look for a high efficiency filter that s merv 11 or. Align one of the standoffs to be in th panel on the pa unit. The roofing filter makes the passband seen by the agc much less narrower and in doing so the weak station is not minimized because of the presence of the strong station nearby. To reduce the amount of rain falling on the roof a more narrow roofing filter is required.

Using merv 5 8 filters will keep your hvac system more efficient than using higher rated filters as long as you replace your filters regularly. For residential furnaces filters range from 4 to 12 on the merv scale. Basically a roofing filter is simply the first if filter in a radio. These narrow filters require that the receiver uses a first if well below vhf range perhaps 9 or 11 mhz.

250 hz 500 hz or 1 8 khz for ssb would be acceptable values. 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. The degree of contamination will depend on several things including the length of time since the last rainfall proximity of the catchment.

The first water to come off the roof at the beginning of a rainstorm is the most contaminated. If the agc cannot see or hear signals nearby in the passband it does not need to use part of its resources to attempt to deal with it. Position the roofing filter in place temporarily as shown in figure 2. 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.

The use of roof washers and roof water filters can reduce the amount of these contaminants entering the system. The top of the board should be just below the top of the shield on the pa unit. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. 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.