[Milsurplus] DU-1 Loop Assembly,

[Mike Morrow]

Joe wrote:

> Just how well did the DU-1 loop assembly work installed inside the
> aircraft.  I was not able to find any info on this.

The information in the manual is interesting, including its suggestions
and comments on the sense antenna.  Mike Hanz has the essential parts
of the DU-1 manual at http://aafradio.org/docs/DU-1.pdf .

> I am assuming it was installed near the radio operator position,
> somewhere in the rear sections of the aircraft. 

On all the pictures I've ever seen of single-engine pre-WWII USN carrier
aircraft with a DU-* loop, it was installed on the top shelf in front of
the gunner/radio operator, about middle of the aircraft under the canopy
between the radio operator and the pilot.  Under that shelf was the RU-*
receiver, and below that the transmitter, typically a GP-*.  The DU-*
obviously had to be easily accessed for manual operation by the radio
operator.

After the innovative 1940 ZB/YE VHF homing system was available, the
photos I've seen indicate that the rather useless (to carrier aviators)
1938 DU-* loops were replaced in short order, well before Pearl Harbor.
For these aircraft, one finds the small ZB-* homing adapter on the top
shelf where the DU-* once might have been.  The ZB-* connected to the
RU-* through an antenna switch box and a pilot's control box for the
ZB-*.

Liaison set RU-* receivers had connections for a loop, but it would have
likely been the similar but external 1938 DW-* loop.

Receivers in the GF-*/RU-* command sets had loop connections.  But the
1941 models like the GF-12/RU-17 would have used the loop connections
for output from a ZB-* homing adapter.  There were dual range coil sets
for these RUs which could be remotely switched by the pilot from an HF
communications band to the 540 to 830 kHz band on which the ZB-* output
operated.  The ZB homing adapter was sized so it could be mounted on
the RU-* in place of the tube cover.  That made a compact remotely
operated command/homing set for aircraft with no radio operator.

The 1940 RAV liaison set receivers CBY-46102 (beacon band) and CBY-46103
(broadcast band) had a loop antenna connection and switch, but the DW-*
external loop would have been utilized rather than a DU-* loop, if at all.

The 1940 ARA command set receivers CBY-46129 (beacon band) and CBY-46145
(broadcast band) had *no* loop antenna connection or switch.  Since the
CBY/CCT-46145 BCB receiver was not used for communications it could be
permanently connected to the ZB's output to eliminate the complexity of
the ZB's antenna switch box and control box.

Loop connections were restored (for God knows what reason) on the 1943 R-23*
and R-24/ARC-5 receivers.  I don't know of any documented purpose or use of
them...they appear simply to be atavistic anachronisms.

The 1942 ARB has loop connections, but they were advertised as present
to support the addition of the ZB homing adapter without use of ZB antenna
switch box or control box.  The ARB has mounting studs for the ZB on top.

All of the above indicate that the days of DU-* loop value were pretty
much gone for carrier- and island-based aircraft after the ZB came out in
1940.  And just a while later, a ZB-* homing adapter feeding an RU-*,
ARA, or ARB receiver became unnecessary after the all-in-one-box AN/ARR-2
VHF homing receiver appeared in 1943.

Mike / KK5F