[R-390] Lankford Filter Mod

[Perry Sandeen via R-390]

Charles and List,
 
Wrote: As I noted in a previous post (7/30/14), any IF
filter added to a 390 or 390A will not be a real roofing filter and will not
provide the advantages that a roofing filter can provide to receivers designed
with other architectures.
 
That may be true but that’s not at all what my post was
about. 
 
I believe the issue is what the filter does or doesn’t do
for improvement of one’s own receiver performance for the money paid.
 
The *roofing filter* mod was real and worked well as an
improvement for its intended purpose regardless of its *Purity of Definition*.
 
Whether the receiver improvement was/is worth the time and
effort is a personal judgment decision. As this mod requires getting into a
small shielded compartment. That is why I recommended anyone considering it to
look at the Y2KRE manual article to see if it was something they wanted/could
do.
 
Wrote: The problem of out-of-band IMD was addressed by
Collins and, for better or worse, the design the engineers settled on was the
multistage tracking RF that we all know and love.  By its nature, this architecture prevents the
use of a roofing filter.  The Collins
engineers COULD (in principle) have added a tracking IF roofing filter, but
they didn't -- and you can thank them every time you align your 390/390A for
not doing so.
 
I think the key word here is COULD. I’m not technically qualified
to comment on receiver design. To me, the word COULD or COULD HAVE means a theoretical
speculation of a concept or situation of something that didn’t happen.  We all do that from time to time on various
subjects
 
You have the benefit of your present knowledge and 20-20
hindsight of 50 or so years. OK. However it was a far different world then. Collins
worked with what components were available, specifications required: physical,
electrical, operational and financial.
 
I would like to see that with your skill set you would
design a plug in DBM first mixer replacement using the LM 1496 for the *A*.  I think that it would be a quantum leap
improvement.
 
And we have what we have or “What it is, what it was, what
it shall be”. We can take it, leave it or change it.
 
For me, being 73 yrs old. I think negative second guessing
of past designs is a complete waste of the few years I have left before I take
the big dirt nap. 
 
So here are the facts as I understand them:
 
We have to work within the physical and some electrical limits
of the receiver we have unless we want to make a whole new receiver. Some have
gone that route.  But then it’s not a
R390A anymore.  OK, go for it if that’s what
you want.  Pink paint with a purple boa,
neon lites and sparkles?  No problem!
 
Please remember, the roofing filter mod was never stated as
a cure for other R390A problems. It maybe that to achieve its best performance enhancement
other mods need to be implemented. 
 
There are over 10 authors that I’m aware of whom over the
last 20 years who have made design improvements.  Some major, some minor. That’s why I added 4
additional chapters of data to the Y2KR3 manual.  When I can get some more round-to-its or some
free help (whichever  comes first) I have
about a hundred pages of more of proven Heretical Goodness upgrades to issue as
a supplement.  I have already released a
two part schematic that incorporates most of those upgrades for those who want
to join the dark side of excellent performance.
 
Regards,
 
Perrier
 
“One test trumps a million opinions” Anon