U.S. Navy DAG-1
1942 RDF
The
frequency range of this RDF, 1.6 to 18.2 mhz., implies that it was not
for navigation, but to seek out the source of enemy radio
transmissions. WWII U-Boats operated in the range of 3.7 to 15
mhz., so perhaps sub hunting was one purpose of these units.
The British used an automatic DF, far more complicated and
much
larger, nicknamed the "Huff-Duff", for HF/DF, or "high frequency
direction finder". The Huff-Duff had an advantage as some U-Boat
transmissions were made very short, in order to thwart DF attempts. So
these units would automatically take a bearing on the signal, and give
an instant read-out. But the Huff-Duff's where apparantly not portable,
as these units are. These portable DAG units would make sense on Coast
Guard
vessels, PT boats, merchant ships, aircraft... anytime direction
finding capabilities were needed on an attack or search craft not
originally equipped with one.
A few interesting things about it are for one the fact that it does
home in on these higher frequencies... other RDF's may receive as high
as 5 mhz., but none that I have seen have a direction finding
capablitity in any range above the broadcast 1.6 mhz. Another is that
it includes a "sense" circuit, a feature which I do not believe
appeared on private sector navigation receivers until after WWII. I
think it is "state of the art" on this Navy unit. The loop has what
looks like a bracket for a compass on it. I think I'll look at Navy and
Army WWII compasses, and I'd bet it will turn out there is a standard
type this was made to fit.
The loop and sense antenna store neatly in the folding door, along with
a ground stake. There is no wire for hooking up the ground, though. It
was probably just a wire with an alligator on one end, and an "O"
terminal on the other. The original set of earphones, in excellent
shape, were still in the small compartment to the right. The openings
for the antennas have watertight screw-down covers, held in place by
bead chains.
Other than the bad paint on the outside of the unit, the inside,
chassis, and even the original A/B batteries are all in fine shape. Of
course I will store the batteries outside the unit. The black speaker
cloth is as new, too. Click on image for larger version.
Miniature tube chassis, in perfect condition. The whole chassis comes
out with the spinning of eight knurled screws. As usual for military
practice, it is designed for easy field servicing. And that is where
the odd wire comes in. When the chassis is pulled, it unplugs from a
female, four prong battery socket. But the nifty "umbilical" can be
plugged into the chassis and the battery socket so the unit can be
powered out of it's cabinet... I assume, for testing while powered.
Tube compliment is (2) 1T4 (screened pentode), (2) 1R5 (heptode
frequency changer), (2) 1S4 (power output pentode). All tubes appear to
be the original RCA components.
Chassis "powered"
by umbilical:
The original batteries, not leaking, or even
swelling. I'm going to do something I've not heard others try, and
maybe for good reason. I'm going to try to get a charge in these
batteries. I'm doing it out of their precious cardboard cases, and away
from all living things... but it's a question I just have to answer...
and I have seen no information on trying this, one way or the other.
Can we guess the results of charging two 90 volt, 50 year old batteries?
This image was from the original ad on eBay. You can clearly see
the two bearing windows around the antenna rotation knob on the left.
The upper one is marked the direction of the antenna when it is
perpendicular to the unit, and the window to the right shows a 90
degree offset, and is labeled "sense". It looks as though, when the
sense circuit is in play, the antenna's orientation is to be 90 degrees
from it's DF position. The later ferrite bar sense circuits did not
need to do this, for whatever reason. When I find a manual I can check
this assumption.
The
frequency range of this RDF, 1.6 to 18.2 mhz., implies that it was not
for navigation, but to seek out the source of enemy radio
transmissions. WWII U-Boats operated in the range of 3.7 to 15
mhz., so perhaps sub hunting was one purpose of these units. 