[R-390] Modification?

[John Vendely]

It's apparently widely believed that the R-1247 was developed for NASA for
use in the space program, but this is incorrect.  An acquaintance who worked
for a NASA contractor in those days once told me that they had indeed tried
using a few R-1247s, but only briefly.  The associated frequency
synthesizers were extremely unreliable, and NASA removed them from service
after only a short time, due to the constant problems.

The R-1247 appears to have been originally developed by Manson Laboratories
as part of the AN/GRC-129, intended as an improvement on the AN/GRC-26 RATT
van.  The transmitter for this set was a T-368 modified for SSB, which
contained a synthesizer similar to Manson's commercial MHS-400 model, plus
the CV-1695, a sideband modulator/frequency converter, also designed by
Manson.  This synthesizer/modulator/converter arrangement was also very
similar to a SSB conversion done by Manson on the Collins AN/FRT-24A.
Manson also later marketed their Model 299 synthesizer, also designed for
the R-390A, which featured an extra loop providing 100 cps steps.

The Manson Laboratories synthesizers were all variants on the same theme--a
serial injection, multi-loop phaselock design developed by them some years
earlier.  They were state of the art for the early 1960s,  particularly in
view of their relatively small size, but were notoriously unreliable.
Although they solved the R-390A's problems with long term frequency
stability, use of these synthesizers greatly degraded its phase noise, one
of the R-390A's greatest strengths.   The R-390A really is a much better
receiver without the external synthesizers.

I have several different types of these old synthesizers, and although
they're fascinating and fun to work on, they require constant fussing to
keep them operational.  They must have been particularly difficult to deal
with in a military environment...


73,

John K9WT




----- Original Message ----- 
From: "Tom Norris" <r390a at bellsouth.net>
To: <r-390 at mailman.qth.net>
Sent: Thursday, October 19, 2006 2:32 AM
Subject: Re: [R-390] Modification?


>
> On Oct 18, 2006, at 11:14 PM, ToddRoberts2001 at aol.com wrote:
>
> >
> > It looks like an R-1247/URR variant of the R-390A. These had
> > external inputs
> > for the 1st, 2nd and 3rd Local Oscillators on the rear panel that were
> > provided by an external synthesizer for high-stability operation
> > and were supposedly
> > used by NASA in the Apollo space program. The radio can be tuned
> > like a normal
> > R-390A without the external synthesizer. Several small relays
> > inside switch
> > it over for use with an external synthesizer when needed. 73 Todd
> > WD4NGG
>
> Yea, it's got the rear panel for it, and from the pictures there are
> some of the cables inside.  I wonder if all the "guts" for the rest
> of it are there?  Only the radio is collectable.  Used to be folks
> like Rick Mish would remove and toss the adaptors and other things
> that were inside.... myself, I have the synthesyser decks, but I'm
> not sure I'd ever use it either since you still have to tune the
> radio to frequency THEN tune the very noisy 60's vintage frequency
> synth decks.
>
> Interesting thing, weren't the 1247's  (I apologize to Barry for the
> typo, I'm really asleep right now) normally later model radios?  The
> Manson radios I've seen looked to be 1967 EAC's - or at least later
> than what appears to be either a 56 or 58 Motorola (with an R-390/URR
> long tag to fill the empty space).
>
> At least this one has the audio transformer problem solved, like
> what's been discussed here on the list.  Looks like there is one of
> the small 600:8 ohm can transformers mounted on a bracket just
> underneath the terminal strip behind the power supply.
>
>
> Tom
>
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