[ARC5] Nomenclature Taxonomy - AN/ART-13B

[Mike Morrow]

Robert wrote:

> ...a photograph of T-412/ART-13B is in T.O. 12R2-2ART13-1 (27AUG52) and
> subsequent revisions through 26SEP68.

Most of my AN/ART-13 library is still packed up, so I referred to T.O. 
12R2-2ART13-1 (15DEC56) and T.O. 12R2-2ART13-2 (30MAR56) at:

 http://bama.edebris.com/manuals/military/an-art13/

The -1 manual there does not have a picture of the T-412, nor any explict
reference to "T-412".  

There is a picture of the T-47A with CDA-T and no EXTENDED LOW FREQUENCY
switch on page 1-2A.  There is text on page 1-1 that defines this as the
AN/ART-13B.  Operation between 1670 to 2000 kHz is not possible.  These
pages were revised on 27AUG52 to add these details.  This sets a date of
not later than 1952 for the first early AN/ART-13B systems.  No new
nomenclature was applied.

Page 2-19 was revised on 15DEC56 to address the EXTENDED LOW FREQUENCY
switch and operation from 1670 to 2000 kHz.  This indicates that the full
modification of T-47A plus CDA-T plus EXTENDED LOW FREQUENCY circuitry
(C151/second S117) was now available.  This sets a date of not later
than 1956 for the first late AN/ART-13B systems.  New nomenclature
T-412/ART-13B was applied.

T.O. 12R2-2ART13-2 (30MAR56) addresses the capabilities of the T-412
by name in detail, including pictures on page 1-2 and 1-4 and the 
schematic on Figure 8-44.  This manual could lead one to conclude
(erroneously, I believe) that there never was an AN/ART-13B that
did not have the full CDA-T plus C151/second S117 mods that were
part of the T-412.

I believe that one can best categorize the AN/ART-13B as follows:

Early AN/ART-13B T-47A/ART-13 with CDA-T and *no* EXTENDED LOW FREQUENCY
                 circuitry.  There is no installed AN/ART-13B nomenclature.
                 The -1 manual revision for this model is dated 27AUG52.
Late  AN/ART-13B T-47A/ART-13 with CDA-T and the EXTENDED LOW FREQUENCY
                 circuitry.  New T-412/ART-13B nomenclature is installed.
                 The -1 manual revision for this model is dated 15DEC56,
                 and the -2 manual revision for this model based on the
                 T-47A is dated 30MAR56.

> ...addition of the dynamotor interlock switch ("first S117") to NT-52286
> or T-47ART-13 is Modification M1 (and replacement of  the 8Q-1 CFI with
> 8Q-2 is M2).

There's also that T-47A VFO dial B backplate with vernier scale to allow
setting one-tenth increments of the minor dial divisions.  That change
is why the calibration book for T-47A/ART-13 is more than twice as thick
as the books for the ATC or T-47.  The vernier permits setting frequencies
on the T-47A in 1 kHz intervals throughout the entire tuning range.  The
ATC and T-47 had books with data at 5 or 10 kHz intervals.

> Final revision of T.O. 12R2-2ART13-2 was 25JUN58...The majority of
> the text implies that if a T-47A went through the 10 to 20 hour 
> conversion process to install a CDA-T, it should have gotten a new
> nameplate and "second S117".

I agree, that's what the -2 manual would imply if one didn't know of
the revision history.  Judging from manual revision dates and the late
"T-412" designation, I think that the full T-412 mod dates from the
mid-1950s, while the first CDA-T installations date from 1952 or earlier.

It's also interesting that the T-412 mod would sometimes be applied to
old USN ATC and T-47 units that did not have the upgrades of the T-47A.
This can only be determined by looking at actual units in the field, and
not from these -1 or -2 Tech Orders which show the T-412 as built from
a T-47A.

And one question remains.  What value was the T-412's capability for
of CDA-T crystal-control in the range of 1670 to 2000 kHz in the mid-
1950s?  That would seem well past the era when the USAF (or even USN)
would have found aircraft operation in that frequency range to be of
enough interest that it was worth the trouble of the modification
required.

Mike / KK5F