Roofing filter
A roofing filtration is often a type of filtration system used in the HF receiver (shortwave radio).<br> It's usually found right after the 1st receiver mixer. The objective of a roofing filtration would be to reduce the passband with the 1st intermediate frequency (IF) to about 6-20 kHz, so that overloading and distortions through the using amplifier stages and mixers are reduced. The receiver's Bandwidth (signal processing) is not determined through the roofing filtration but by a using crystal filter, mechanical filter or DSP filtration. These enable significantly far better filtering curve than a roofing filter, which often makes use of a high 1st IF of higher than 40 MHz. Since of this, roofing filters are usually crystal filtration types.
Although a 6–20 kHz roofing filtration system is acceptable for standard intent HF radio reception, demanding uses like listening to weak CW or SSB signals demands the utilization of roofing filters that are a much smaller width appropriate towards the reception mode in use. 250 Hz, 500 Hz, or 1.8 kHz can be acceptable values. These also need that the receiver employs a lower primary IF below VHF selection, maybe 9 or 11 MHz.
