[Milsurplus] DU-1 Loop Assembly,

[Mike Hanz]

KK5F did his usual outstanding treatment of the subject below.  One has 
to remember that the DU was originally intended to be used in open 
cockpit aircraft.  The metal reinforcements of a Plexiglas® canopy, 
which is pretty much the only remaining deployment by the time the war 
started, does introduce some deviation in direction finding, but at 
least it would get you in the ballpark.  The original DU was a sort of 
second generation development of the Navy RDF-1 coupler/loop, which 
shares its overall appearance and even the bands to 8MHz. Anything over 
1.5MHz was useless for DF work and offered real dangers for 
misinterpretation, so the DU-1 and DU-2 were throttled back to the 
1.5MHz limit.

For the die-hards, I posted the entire 55 page chapter on Navy DF 
development and use (circa 1936) in the documents section of my website:

http://aafradio.org/docs/1936_NRL_Aircraft_Radio_Training_Manual_DF_Chapter.pdf 
is the link.  Be aware that it is 14MB in size.

I took a photo of a typical installation of a DU-1 with an RU/GF set in 
an OS-2U Kingfisher in the Smithsonian collection - it's at the very 
bottom of http://aafradio.org/flightdeck/Peripherals-mikes.html (the 
Kingfisher is currently suspended above the Enola Gay at the Udvar-Hazy 
Museum near Dulles airport for those interested.)

73,
Mike  KC4TOS

On 7/23/2012 3:00 AM, Mike Morrow wrote:
> 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.