DDR Type 2 Short-wave spy transmitter (opens in new tab)

Are you certain you want to be compared with the Stasi?

I don't think there are any border disputes in this area.

Perhaps the hobby-archaeologist wanted to remain anonymous because unearthing historical artifacts with a metal detector is illegal in some places. In Germany one needs a permit at least and must leave finds undisturbed so that archaeologists can see the context of the find. If the hobby-archaeologist is searching illegally, then he/she may be afraid that the location of the find may lead to him/her.

That railway and strange border is an old remnant of the Treaty of Versailles.

Conformal coating is used, which is a thin layer of polymer sprayed as a film over the finished and soldered PCB.

As modern components are normally much smaller and sit fairly flush with the PCB, there are less nooks and crannies, and so the coating manages to fill them all or bridge them over quite well. It's still not a step used in most PCBs, there are downsides like requiring connectors and switches to be masked off with tape, and so it is reserved for more extreme applications than consumer electronics. Think electric gate control boxes, or marine electronics.

It would probably have existed in some form at the time of the OPs radio, but spraying the PCBs in it wouldn't have saved all the connectors, switches pots and other front panel controls from moisture, and so a more general method was needed.

Finally, a more extreme step is to "pot" the entire PCB by putting it in a sealed container and filling the container with a "potting compound", a liquid resin that sets solid or to a rubbery finish. This makes replacing or repairing the PCB very difficult, requires a lot of thought as to connectors, and it doesn't work well for high power electronics as the potting compound traps heat. It allows you to fully submerse a PCB in water forever, stops sparks if your PCB is working around explosive gases/powders, and is sometimes used as a "security" method in hardware security modules or "secure" USB keys.

For security, potting only really works if tiny wires are embedded in it, which on breaking wipe the encryption keys. Scraping off potting compound can otherwise be done by anyone if they are willing to spend a long time.

> A question though: how is humidity handled in modern electronics? Is there any sacrificial used on mainboards

For consumer electronics it generally isn't handled. If you look at the edges of the boards you'll see that they are rough-sawn and not sealed and that there is not conformal coating elsewhere on the boards. Note that while FR and hardpaper material are hygroscopic, the epoxy cases of chips let moisture pass as well.

Conformal coating or potting. Simply not exposing the components and board traces to environmental conditions at all is simpler and more effective - but then we no longer expect to need to replace vacuum tubes very often.

The disguise was for transport. There was very little chance that it would be discovered once underground and even if it were, it would not compromise the owner as it would be located far away in a place like a wood or a public park.

Here's how it may have went down:

> Digs around in forest for no good reason

> Finds car battery

> Rattles

> Opens it

> Western radio inside

> "Oh shit, a cache of an allied spy. I better put this back where I found this and tell no one ever."

While it's true that a dumped car battery would at least raise interest or even suspicion, a buried one is significantly harder to stumble upon, however suspicion is still optional. Who is going to open a potentially highly acidic/hazardous car battery anyway? Something "rattled" inside, which suggested it was dry, and what ever rattles inside a car battery, everything is supposed to be fixed there, right? Besides, an ancient Varta battery - put that in a museum! There - the cover's blown.

Back in the days no one cared about dumped car parts. But nowadays just about anything raises instant suspicion if anything out of the ordinary lies about on the ground.

Are we sure it was buried intentionally, and not moved from its original place and eventually thrown away (presumably because the concealment worked as intended and it looked like a junk old battery) to where it ended up now?

I can't edit my other comment, but I did think that it accomplished its mission.

> ensuring that anyone who stumbled across it would be suspicious.

Or the person who was meant to retrieve it would know what they found. "It's inside the car battery buried in ..." is a pretty easy instruction to follow.

The instruction can also be hidden in plain sight – a car battery is ordinary enough that no one is going to be suspicious if you write it down on a piece of paper. You can even hide the location in order or invoice number pretty easily.

If someone found it, they may be suspicious. If I found one my first thought would be that is just some junk someone threw out (you can't put car batteries in normal trash where I live). It is fairly easy to notice if dirt has been recently disturbed, even from afar (which his good if you're worried about getting caught).

TL;DR burying something in a car battery is actually pretty clever.

It did stay hidden for 30+ years

This is a transmitter, it can't receive replies.

But yes, they tested it:

> The transmitter produces a strong and stable signal at the fundamental frequency, but also produces strong unwanted harmonics, with the f2 being only 3dB down. Furthermore, the f3 is only 10dB down and the f5 is just 20 dB down.

But Stasi ceased to exist in an orgy of shredding, so it might very well have been forgotten.

I wonder if there are any news articles about what else might have been found in the cache, and where it was found?

Edit: Just hadn't read far enough...