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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.

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