[R-390] Filters

[Jim Haynes]

Rockwell-Collins still makes mechanical filters, but it's my understanding
they use a different principle from the older ones, and also that the
interface requirements are different.

I see by a web page that they make a low-cost series for use in 455 KHz
IF circuits, with bandwidths of 300, 500, 2500, 5800, 7000 and 10000 Hz.
Naturally they don't say what "low" means in cost.

jhhaynes at earthlink dot net