troyunrau

Sometimes people get caught up trying to find exact matches for software, when instead it's a combination of tools that gets the job done on another OS. The annoying thing is learning new toolsets -- but it's only annoying until you know them.

I appreciate your caveat about peak load. Fortunately for this device it is largely irrelevant. It's so old school and analogue that there isn't a standby draw -- it's either on or off. Its operational time is measured in days on a single 9V.

It might be interesting, so I'll describe the instrument. Starting with some VLF background:

There are a number of VLF stations scattered around the world -- for example station id NAA in Culter, Maine (24.0kHz) -- used to communicate with their submarines while submerged. If they only transmitted when they had something interesting to say to the subs, that would be useful information to an enemy. So they have to transmit continuously (except for on scheduled maintenance days for the transmitters). These are very powerful huge antennas, often spanning entire valleys -- after all, the wavelength at 24kHz is enormous. Different stations have different frequencies and we know about most of them.

At a sufficient distance away from these antennas, all incoming signals are polarized due to reflecting off the ionosphere. These radio waves pass over linear conductors in the ground which will distort the polarization. What we're effectively measuring is the distortions in these incoming radio waves to map the locations (and orientations) of linear conductors (natural antennas) in the ground, up to about 250m below surface.

So this device is used to measure the incoming signal direction and polarization. It does so by setting up a harmonic oscillation on the device and emitting a tone. There's a couple of magnetic coils on the device, and as you swing the device about, the received signal from the transmitter and the onboard oscillator will constructively or destructively interfere, changing the tone. You note the direction the tone is the strongest using a compass and inclinometer (both analogue) and write it down in a notebook. Then move to your next position and repeat.

Prospectors have been using this for five decades at least.

But as you can see, not a complicated thing from an electronics perspective. The only complicated thing is tuning the on-board oscillator properly.

Mild acids that are food grade are great because you don't have to worry about occupational health exposure. A lot of people use vinegar. I use citric acid -- which you can find in the grocery store in the spices section. Citric acid is what makes sour candies sour. You buy it as a powder.

I mix a little water and citric acid and let the part soak in it, then brush with a soft wire brush (not steel wire, as it's too hard and will scratch the parts too much).

But, as a tangent, buying stronger acids is pretty easy, depending on the acid. Hydrochloric acid is sold in hardware stores as muriatic acid. Sulphuric acid is used to recharge lead-acid batteries. You'll have a harder time finding nitric acid (because people can make explosives with it) or hydrofluoric acid (cause it is actually deadly as fuck), but industrial suppliers often have them. I wouldn't handle any of these without some training. Even muriatic acid will off-gas chlorine and cause all the tools in your shop to rust if stored improperly. (From experience.)

I agree. However the Ah capacity of a modern 9V is pretty good compared to the 70s. Unless you buy the cheapest 9V crap you can find ;)

I use citric acid on a lot of connectors when the pins are corroded (for the same reason). Revived a lot of cables that way. Good advice :)

The whole battery mounting board is shot -- entire traces corroded on it, and the contacts have effectively dissolved.

Fortunately, the machine was designed in 1977(ish) and batteries have gotten a lot better since. 6x AA batteries can now be replaced by a single modern 9V and it'll deliver enough current. So I'll mount a new 9V holder and solder it into the battery board wiring harness. I've already tested that solution on the breadboard and the machine appears to work.

Duracell rep might be a sales robot. Or possibly talking about another type of battery? Anyway, points for learning :)

Probably about 4mm across.

Needs some baked beans for scale. One baked bean spider in size.

These batteries are in a circuit which has a physical power switch separating it from the device, meaning there should be zero parasitic drain while off.

Thus I conclude your fun fact to be apocryphal.

The instrument is fully analogue, designed in the late 70s. The serial number on the device implies it was manufactured in 87. I contacted the manufacturer and the last person who could service it has long since retired, but they sent me the calibration and tuning documents so I might be able to revive this beauty.

12 years ago. Now you'd deepfake it :/

I didn't build it. Just renting it for Thanksgiving weekend (Canada) with the family