[Milsurplus] ARR 15, how to narrow selectivity???

[Mike Morrow]

>My Collins R 105A ARR 15 is now working perfectly including the
>wonderous electromechanical autotune. It is as broad as a barn door
>however?and I'd like to narrow it wothout butchering the radio.
>
>This rcvr has a variable IF as part of the tuning so a fixed freq
>xtal or mech filter does not seem useful.?

No, it won't be.  The AN/ARC-2 and -2A also employ a similar type of
variable single-conversion IF, FWIW.

>I guess I could make a tunable outboard additional IF stage,
>but that seems extreme. Any practical ideas?

When in CW mode, a narrower built-in audio filter is switched in.  For
greater sensitivity, perhaps the easiest thing to do is use an external
digital audio filter.  It shouldn't be too critical...no one is going
to count on one of these as a contest receiver today.

I have many fond memories of my first AN/ARR-15 receiver.  In 1969 I 
got an R-105/ARR-15 through Navy MARS.  I used it as my only general
coverage receiver for years.  I even took it and an Elmac AF-67 to my
room at ratty Ga. Tech freshman dorms to check MARS on CW at 6970
kHz.  It was a very useful receiver, and could easily be set within
1 kHz accuracy.  For CW and SSB, tuning could be performed with the
calibration set knob rather than just the main frequency control.
I used an AC-powered 28 vdc supply for the dynamotor, but to get rid
of all the ripple I had to put an electrolytic across the HV, internal
to the receiver.

I wish that the R-105 covered 200 to 520 kHz (like the BC-348 and the
R-648/ARR-41).  I enjoyed listening to merchant marine CW from
420 to 520 kHz.

So...try a modern external audio filter.

Mike / KK5F