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.

How to use roofing filters.

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. Align one of the standoffs to be in th panel on the pa unit. 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. 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. There are two basic designs for modern radios. The top of the board should be just below the top of the shield on the pa unit. For residential furnaces filters range from 4 to 12 on the merv scale.

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. The first water to come off the roof at the beginning of a rainstorm is the most contaminated. If your family has health or allergy issues then you may want to look for a high efficiency filter that s merv 11 or. These narrow filters require that the receiver uses a first if well below vhf range perhaps 9 or 11 mhz.

Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. Position the roofing filter in place temporarily as shown in figure 2. The degree of contamination will depend on several things including the length of time since the last rainfall proximity of the catchment. The use of roof washers and roof water filters can reduce the amount of these contaminants entering the system.

It is usually placed as clos e to the first mixer as possible in order to be effective. 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. 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. 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.