N8KDV wrote:

Mike Maghakian wrote:


one myth I believed for about 25 years was that a filter rated at 6KHz
at 6db had a 6 KHz bandwith at 6db. that is not true.


Yes it is true! If one looks at the plot of the response of the filter,
and if it is 6 kHz wide at the -6db point then that's exactly what it is,
6 kHz.... at the -6db point... not 8, not 12, not 4....

With some of the cheapeast ceramic filters, I think this
varies from sample to sample -- that is, some samples may be
6kHz wide at the -6db point and other samples not --
nonetheless, all samples of the same model receive the same
nominal rating. However, "performance" filters tend to be
more consistent. In any case, a radio manufacturer can
select which samples go in its radios and which ones get
rejected. For bottom of the line radios (esp. cheap
portables), manufacturers are probably not so discriminating.

--
M2