Mike ) writes:
In article ,
craigm wrote:

The filters in the 800 are not "right out of the R8". The Sat 800 has a 455
kHz 2nd IF while the R8 uses 50 kHz.

Which are not filters and have nothing to do with anything.

The Sat 800 uses ceramic filter while
the R8 uses LC filters.

The designers may have chosen to use the same bandwidths, but the filters
are not the same.

Since the R8/SW8/S800 were designed by the same people (Drake), the
bandwidth filters are the same. That's what I was talking about.

But there is more to a filter than bandwidth. You can have a nice
narrow filter that turns out to be lousy, because it has no sharp
skirts. So it broadens out really fast, and lets lots of adjacent
signal in, unless it's terribly weak.

"Selectivity" is often easy to get, but the shape factor is what
separates the quality filters from the rest.

Comparing bandwidths often doesn't mean anything.

And the frequency of the IF may indeed be a factor. Not maybe
in itself, but in the design that goes with it.

The previous poster is implying that the ceramic filters at 455KHz
may be relatively run of the mill, that whatever the stated selectivity
the skirts aren't sharp. Dropping to 50KHz has always allowed Drake
to make filters out of coils and capacitors, and that provides more
leeway in design. They aren't picking some premade filter out of
a catalog.

It's not really an issue of IF frequency, but it's easier to make
good LC filters at 50KHz than 455KHz, which makes sense since it's
a lower frequency. But it is the type of filter that matters. If
the Satellite used a Collins mechanical filter at 455KHz, paying
the premium for a premium filter, the shape factor is far better
than the average ceramic filter, and could beat out the Drake's
50KHz filter.

Michael