[ARC5] Re: [Milsurplus] Hosstraders... Now ART-13

[Mike Morrow]

I wrote:

> ...the USAAF/USAF T-47A/ART-13 has a vernier scale on VFO dial B
> that allows setting it in tenths of a division, and a power interlock 
> switch that activates when the top cover is removed...

> ...The T-47A uses a different calibration book than the T-47 does.
>
> The LF oscillator that should be in a T-47A/ART-13 is the
> O-17/ART-13A, which only covers 200 to 600 kc in three bands.
> The LF oscillator that should be in a T-47/ART-13 is the
> O-16/ART-13, which covers 200 to 1500 kc in six bands...

John wrote:

>I posted the original question about the differences between the 
>13 and 13A. I'd intended the question as more of an inquiry about
>the relative features and performance of the 13A compared to the
>13. I know there were changes made to the external antenna coupler
>and related things, but is the 13A distinctly better?

John,

If one is attempting to duplicate a USN airborne HF installation for use with any USN receiver (like an ARB or AN/ARR-15), then the ATC or T-47 and NOT the T-47A should be chosen for the purely historical reason that the USN generally did not use the T-47A (or the T-412/ART-13B).  The T-47/ART-13 and the R-105/ARR-15 together with the C-740/ART-13 and C-733/ARR-15 control panels make up most of the AN/ARC-25 set.  If a LF oscillator is included, then it should be an O-16/ART-13.  A DY-11 or -12/ART-13 dynamotor and CU-25 and -26/ART-13 external LF tank coils should be used.

If one is attempting to duplicate a USAAF or USAF airborne HF installation using the AN/ARR-11 (BC-348-*) receiver, then the T-47A should be chosen, since the T-47A is a USAAF unit.  The T-47A/ART-13 and the BC-348-* make up most of the AN/ARC-8 set.  If a LF oscillator is included, then it should be an O-17/ART-13A.  A DY-17 or -17A/ART-13A dynamotor and a CU-32/ART-13A external LF tank coil/antenna switch should be used.

>If so, how and why? What is the rational for the changes made in the 13A?

If selection of a T-47 or the T-47A is NOT based on historical alignments such as detailed above, there is NO real significant difference nor advantage of one over the other.  I like the USAAF's T-47A because the vernier scale on VFO dial B and the associated calibration book allow frequencies to be set at 1 kc intervals across the entire frequency range of the T-47A.  The USN's ATC or T-47, in comparison, has no useful vernier scale on VFO dial B, so the calibration book contains data only at 5 kc intervals below 8 mc, and 10 kc intervals above that.  However, on any specific frequency contained in the calibration tables for both the T-47 and T-47A, the data is the same.

The saftey interlock when the top cover removed is also a feature that the ATC or T-47 lacks.

As Robert said, many T-47/ART-13 units and other components are just re-nomenclatured earlier USN ATC or ATC-1 units.  Sometimes, only a yellow paint stencil was used to mark the new component number in the black crackle paint.  The old MT-161/ART-13 transmitter mounting system was replaced with the MT-283 and -284/ART-13 mountings in both the USAAF and USN.  The T-47A units would tend to be a little younger than the ATC and T-47 units.

Some T-47A/ART-13 units had a CDA-T crystal-controlled oscillator backfit for 20 MF/HF crystal controlled channels, and there was also some of the same units with a new nomenclature of T-412/ART-13B.  A modified C-87/ART-13 had to be used with this set to allow selection of the 20 crystal-controlled channels. 

The O-16 and O-17 LF/MF oscillators can be used in either the T-47 or T-47A, but normally they'd be found as indicated above (16 with 47, 17 with 47A).

Mike / KK5F