[R-390] Filters

[John Kolb]

Yes, newer design mechanical filters have low insertion loss,
but R390A filters are spec'ed at 25 db max, typical of older
designs.

I put the data sheet for the F455N-20 filter on my web site,
but then for the first time ever, my 300 MB/month bandwidth
was exceeded, so I guess a bunch of you found it of interest.
Perhaps someone who grabbed it can make it available elsewhere.

"Filters" has been one of the most active threads I've 
ever seen on any of the groups I watch, and is very interesting.
Good luck to you, Quartz, as you attempt this difficult
repair - I've never attempted anything more difficlt than opening
filters, cleaning or repairing coil wires.  Hats off to you all
who rewind coils.

John  KK6IL

At 09:01 PM 2/18/2013, you wrote:

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