[TowerTalk] Roofing Filter

[Tom Rauch]

The November issue of World Radio will have a detailed
article on that very topic. A roofing filter is the first
selective filter in a receiver containing multiple narrow
selectivity or filters. It is normally wide enough  to allow
noise blankers to function and passband tuning to work. It
provides a "widow" that limits maximum obtainable bandwidth.
The Drake R4C is a good example of a receiver that really
sucks for overload within the passband of the roofing
filter. That's why a 600Hz wide roofing filter or USB/LSB
roofing filters are required for decent R4C performance.
Most DSB based receivers, even the VERY expensive ones, are
also very poor within the passband of their roofing filters.
In some cases, like in the Orion, the roofing filter can be
switched to match the mode. This makes the Orion receiver
exceptionally good for close signal performance in all
modes, despite the fact it has a DSP system.

73, Tom W8JI


> This is probably "Stupid question No.1", but- here it is.
I have been
> trying to get a definition and/or description of a Roofing
Filter. The ARRL
> handbook, because of its pitiful indexing system, is worse
than useless.