How To Use Roofing Filters

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

How to use roofing filters.

Align one of the standoffs to be in th panel on the pa unit. The top of the board should be just below the top of the shield on the pa unit. These narrow filters require that the receiver uses a first if well below vhf range perhaps 9 or 11 mhz. There are two basic designs for modern radios.

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. Basically a roofing filter is simply the first if filter in a radio. Using a more narrow roofing filter can eliminate this unwanted signal and eliminate the agc pumping. 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.

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

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 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. 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.

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. 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. Position the roofing filter in place temporarily as shown in figure 2. If your family has health or allergy issues then you may want to look for a high efficiency filter that s merv 11 or.