On Sat, 19 Jul 2014, dave wrote:


Very , very difficult. Even after it is close enough(!)in resonant
frequency- there are a few MORE extremely critical parameters involved ...
This is why true "Crystal Filters" were so expensive,even when they were
mass produced ...


You can get nice 5 pole filters for about a hundred bucks can't you (I
haven't checked for a few years). For relatively wide band SWL cascaded
ceramic resonators should suffice).

Expensive is relative.

I remember wanting an SSB filter for something about forty years ago, and
they were maybe forty dollars, expensive for a kid on allowance. I
thought a replacement part would be cheaper, but checking with Heathkit
for one of their SSB filters turned out they were more expensive. I
eventually found a second hand filter, though it clearly had never been
used.

So I suppose a hundred dollars now is a better price, but still one of
those more expensive components.

And consiering the cost of replacement filters (or even optional filters),
a receiver or transceiver must be pretty cheap since it includes not only
the filter, but all the other parts. I suspect they get a good deal for
bulk purchase, but don't pass it on for people wanting to buy a
replacement filter.

Ceramic filters, if you can live with the low IF, obviously has provided a
much better level of filter without the cost of crystal or mechanical.

Michael