[R-390] Filters

[Drew P.]

Bob Camp wrote:
[snipped]

"A narrow mechanical will have less insertion loss than a narrow LC filter (higher Q counts). With a gain stage or two you could fix that. It would make straight drop in a bit more complex."

IIRC, the Collins mechanical filters used in the R-390A have a very high insertion loss, even when working as designed.  This would be a reason why they were placed AFTER the first 455KHz IF stage.  If these filters indeed have high loss, then perhaps no additional gain stage would be required when substituting a many pole LC filter for mechanical. Lossy original filter, lossy replacement.

Drew