How To Use Roofing Filters

A basic merv 4 filter will likely be the cheapest but won t catch certain small particles like dust mites and pet dander that could be in your home.

How to use roofing filters. 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. The first water to come off the roof at the beginning of a rainstorm is the most contaminated. The use of roof washers and roof water filters can reduce the amount of these contaminants entering the system. The term roofing stems from the fact that it protects the rest of the radio following it from out of the passband signals.

O needs vhf roofing filters wide cheap or narrow expensive o excellent image rejection o close in dr varies down conversion architecture 9 mhz typical 1 st if o performance near if is not uniform o image rejection near ham bands requires design attention o needs only hf roofing filters narrow cheap. To reduce the amount of rain falling on the roof a more narrow roofing filter is required. The degree of contamination will depend on several things including the length of time since the last rainfall proximity of the catchment. 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.

If your family has health or allergy issues then you may want to look for a high efficiency filter that s merv 11 or. If you are susceptible to allergies asthma or other respiratory conditions then you may want to use a filter with a merv rating of about 9 to 12. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. These narrow filters require that the receiver uses a first if well below vhf range perhaps 9 or 11 mhz.

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. There are two basic designs for modern radios. Basically a roofing filter is simply the first if filter in a radio. 250 hz 500 hz or 1 8 khz for ssb would be acceptable values.

For residential furnaces filters range from 4 to 12 on the merv scale. Position the roofing filter in place temporarily as shown in figure 2. 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. It is usually placed as clos e to the first mixer as possible in order to be effective.