wrote:
wrote:

As a demod filter? I would image a low order active filter to clean
things up. Remember, this is the audio band, not RF. I've seen some
write ups on 455khz IFs being done with active filters.

Kiwa sells an active filter for 455Khz
http://www.kiwa.com/kiwa455.html

Note the AR7030 has "tone controls", so certainly it has an active
filter past the demod. The problem with building LCR filters in the
audio band is they are bulky, not to mention often inaccurate. With
active filters, you have more flexibility over component values.

Drake uses an LC filter in the IF. They "Get away" with it becuase of
the
lower IF they use. R390s, original not the R390A, and the R392 use
several staged of LC filters and have excellent skirts.

Except we are not talking about IF filters .The "fading" filter is at
the end of the chain, i.e. past the demod.


The Kiwa filter you refference is not a "active filter", but a ceramic
filter
with amplification. To me active filter means opamp or norton amp
with feedback to control pass/reject charactoristics. The premium Kiwa
unit is nearly as good as a crystal or mechanical filter and MUCH
easier
to connect. I installed one in a friends R2000 and was impressed by
the quality and how well it worked.

A big advantage of passive LC filters is they are much less "fussy"
then active filters. I like not having to mess with power and proper
bypassing.
And if you are willing to wind your own torroids, it is pretty easy to
get the
L very close to what you want. The C can be built with standard value
caps in parallel.

Except this is at audio frequencies, where the component sizes are much
larger. Again, this is not at IF frequencies.




The Tone-Tilt filter I used in all 3 of our R2000s is active because it
would be
VERY difficult to use LC filters effectively.

Terry