Reproduction 1909 Marconi Direction Finder

We have a 1909 Marconi Direction Finder at the SPARK Museum of Electrical Invention that is missing a section called the “Goniometer”. Rather than display the piece with a huge hole in the front I constructed a replica of the Goniometer, using an original as a guide. Here is the original on the left with the repro on the right, aged & stressed to match as best I could:

All of the engraving and some of the cutting was done on the Glowforge. The rest was done in my machine shop (actually, the GF is in my machine shop, but you know what I mean).


This is amazing work. Once installed, it would take a true expert to notice it is a reproduction. They are blessed to have you at the museum.


That is an amazing reproduction!

Not sure how it works, but it looks like the center is rotated 90 degrees from the outer dial on the original.


Wow, skills.


Ha! I was wondering if anyone would catch that. Nice attention to detail!

Edit: Hey Bill, I checked, & the orientation on my repro is correct. At some point someone must have disassembled the original one & put it back in the wrong position!


you should share that on twitter and tag adam savage. he’d be all over that, you’d probably get a nice retweet.


Wow, that’s amazing! No one would ever know it wasn’t original.

Yup. Looks like a goniometer to me, too…

( A “goniometer” is a device that measures an angle or permits rotation of an object to a definite position. In orthopedics, the former applies more. The art and science of measuring the joint ranges in each plane of the joint are called “goniometry” .)

Thing is I always thought it was “goinometer” and “goinometry” because my dad said it was how you could tell what direction something was “goin”…


Well done

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Nice work!


Great job! I’m sure you … and everyone else was thrilled with the outcome.

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If you didn’t tell me, I wouldn’t know the original from the reproduction. Amazing!

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That makes way more sense! I thought that was a really strange orientation for zero.

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A Marconi Direction Finder is a radio direction finder from the very early days of radio. I’m guessing on the details because I’m too lazy to look 'em up. But I would guess there’s a directional antenna someplace (probably a large loop) that should attach to this device, probably mechanically but maybe it drove an electric motor (need to see inside). You turn the knob and the directional antenna rotates proportionally. The signal strength has to be monitored somehow (would probably have been done “organically” by an operator with an earphone), and the bearing to the radio transmitter would be the direction the antenna is pointing when the signal is strongest. It probably would have been referenced to the front of a ship, so 0º would be dead-ahead. The radio operator could determine the direction to steer to intercept a ship in distress. “Steer 37 degrees to port!”.

This type of system was the primary method of locating ships at sea for a good part of the 20th century. The technology obviously would have improved significantly, but the basic idea of pointing a rotating antenna at the source of a transmission to determine the bearing to that source didn’t change until everyone started using GPS.


Yes, that is essentially it. In this case there were four fixed loop antennae, one set fore/aft and another port/starboard. Here is a schematic of the set:

Ah. That’s actually quite a bit more sophisticated than I thought. Though I’m going to have to stare at it for a bit to figure out how it works.

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THAT is super cool!

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Keep staring.
Let me know when you figure out where the macaroni fits in… I can see where you wind the pasta around your fork…
Screen Shot 2021-02-17 at 5.19.41 PM
…but after that, I get lost…


Essentially it takes the phase difference between the four antennae & amplifies it, so the goniometer is adjusted to the strongest signal, & the direction is read off the dial. Very rudimentary, 1st generation radio direction finding.

Yeah. I understood it was using phase in lieu of rotating the antenna. But I don’t see how the phase gives 'em 360º. I’m thinking it should only be good for 180º. Not that this forum is the place for such a discussion… but don’t tell me if you understand it, anyway. I’d rather try and suss it out myself. Though worst case, I’ll ask my dad who’s got an “old school” MS in EE, from the days when everything was still analog, and he’ll enjoy explaining it to me. :slight_smile:. My education is more digital than analog.