On Tue, 14 Feb 2017, Ralph Mowery wrote:
In article ,
says...
I recently saw a notice that Rockwell Collins has stopped production
of Mechanical Filters.
Many of the newer radios are starting to use electronic circuits or more
likely software fro the filtering now.
Many newer radios do not have much RF circuity in them, mainly
microprocessors doing most of the work. This trend started about a
dozen years ago and is progressing more and more every year.
Instead of being limiated to just 2 or 3 filters (that often cost around
$ 100 each) you just turn a knob or move the mouse and set up any type
of filtering you want.
That's why in the past, some receivers went down to a 50KHz IF, if you
wanted a selection of filters, it was cheaper using LC circuits down there
than a bunch of crystal or mechanical filters at some higher frequency.
It is amazing. Even the low end shortwave portables are using ICs that do
a bit of RF handling, and then down to where it can convert to digital.
SO you have ICs that offer more than a given receiver provides, the
modification now consisting of changing the firmware, or bypassing the
internal microprocessor, and controlling it through another computer.
And of course the high end receivers are going the same way, except they
use better circuitry. Build the circuit once, and then you can do endless
things like changing selectivity or adding different types of
demodulators.
Michael