This particular bay was really an afterthought. Until the prospect of amateur work being possible below 500kHz, inclusion of any of the navigation receivers
seemed to be inconsistent with the general rule for the fight deck - "Everything should be useful, at least in some fashion." If I keep my weight down to a 96 pound
weakling or really "suck it in", just enough room is left in the entry gap into the octagon shaped array of racks
to accommodate a vertical column of the most common manual and automatic direction finding receivers used during the war. These receivers were teamed with loop antennas
and not only found application as radio range beacon receivers, but also functioned as independent direction finders on signal sources whose position was known, such as
AM broadcasting stations. Often the aircraft had both kinds of receivers, one of those depicted here and a MF command receiver such as
the R-23/ARC-5 or BC-453 to handle the radio range system. That allowed cross checking bearings (at least where the radio range was established), though in the vast
reaches of the Pacific or in forward battle areas of either theater, the larger receiver was often the only one providing any accuracy. The control boxes for
these receivers are mounted to the right of the bay and are shown on a different page - Navigation Panel
Beginning at the top is a dual purpose receiver, the Bendix RA-10. It actually doubles as both a navigation set and an HF receiver, teamed with the
TA-12B transmitter just out of view to its right. The frequency range of this particular set
(an RA-10DB) is 150-1,100kHz and 2.0-10.0MHz. The antenna is shown at the bottom of this page, a manually steered loop that (at least in the AAFRadio shack) is
shared with the MN-26 receiver below it.
Below the RA-10 is another well known nav set, the Bendix MN-26. These receivers came in a surprising
number of variations. Though all similar in appearance, different frequency ranges were available
for different theaters, leading to a frustating time trying to match the control head with the receiver.
This particular one is an MN-26LB, and has bands of 200-410kHz, 550-1,200kHz, and 2.9-6.0MHz. It is the
one peculiar version of the MN-26 series that is also known as the AN/ARN-11.
Perched on top is a small ferry beacon receiver, employed with the radio range system in aircraft
that needed to be moved from one place to another but had yet to have a radio
compliment installed. This was fairly common during the time when the destination
of a particular aircraft out of the factory could be either the European or Pacific
Next in line is the Navy's primary "big gun" DF receiver - the DZ. This is a
model, and employs a sophisticated goniometer crossed loop design by RCA. This
loop was rotated manually by a knob at the bottom of the loop assembly, limiting
its placement within the aircraft to a position near the navigator or radio operator.
The frequency coverage of this set is a remarkable 15kHz to 1,750kHz in six bands
(15-32.5, 32.5-70, 100-200, 200-400, 400-800, and 800-1750kHz.) The separate dynamotor
is shown below. It provides 220 volts DC at 60mA.
Below that (unseen in this photo) will be what both the Navy and USAAF finally settled on
toward the end of the war as the joint DF solution - the AN/ARN-7. An evolution of the Bendix
SCR-269 and its predecessors, it offered completely automatic loop slewing when the
signal was strong enough. Below it will be mounted
an AN/ARN-6, which used a variation of the DZ antenna design to minimize the
exposed size of the loop structure. Both of these are automatic DF units, which
is to say a frequency was dialed in on the control box and the antenna slewed
automatically until the direction was indicated on a servo controlled indicator.
The antennas for these receivers are all rotatable loops, some more complex than
others. Several of these are shown below, eventually to be installed in the ceiling
of the "flight deck"
DZ-1 loop antenna
DZ-1 control base
LP-31A loop antenna for ARN-7
MN-20E loop antenna for MN-26 and RA-10 receivers
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