SOLVING the Mystery Behind a Soviet Spy Bug : A True Masterpiece of Technical Elegance!

How did a Mysterious Microwave Bugging Device operate secretly for SEVEN YEARS inside the US Ambassador's study in Moscow with NO power source? As I'm an inquisitive and practical sort of chap, I MADE one for a BBC TV series with Professor Hannah Fry to discover EXACTLY How It Works!

In this episode of Machining and Microwaves, I do a deep technical dive into precisely HOW this totally passive mechanical contrivance worked as an undetectable covert bugging device. It has no active components, no battery, no wires and needed no modifications to the building.

Is this semi-magical Great Seal Bug somehow connected with infamous Moscow Signal?

There's a sneak preview of some of the machining work, but everyone wants to know the REAL MECHANISM behind how this weird "Thing" operates. I machined a batch of replicas and carried out practical experiments to uncover the REAL way they work.

Over the years, there have been lots of articles and academic papers which tried to analyse the way the "Thing" worked, but there is a lot of disinformation and obfuscation (and book sales!) involved, so the truth tends to get pushed aside in favour of a cracking yarn (and book sales). The CIA, FBI and US Naval Laboratories, as well as UK counter-intelligence specialists all had a go at analysing and reproducing the device, then improving it and making even MORE subtle and clever bugging devices, but this was probably the first.

Lev Termen, more commonly known as Leon Theremin, was the engineer behind it's creation, but I'll be covering his fascinating part of the story in a future episode. His life has even more folklore, fabrication and disinformation even than the Creation Myths of the Great Seal Bug.

So, buckle up for a deep dive into the Tech and Physics of how this magnificent piece of 1940s technology REALLY works.

Graphs and maths are made using Grant "3 Blue 1 Brown" Sanderson's Manim software running with Python 3.10 in an Anaconda environment. 3D CAD and mechanical vibration simulation using Fusion360, editing by Davinci Resolve Studio, electromagnetic simulation with OpenEMS running under GNU Octave. Microphone is a Shure SM7B driving a Zoom F3 audio recorder. Cameras are Sony alpha 7 IV, Sony ZV-1 and iPhone. Before you ask, I copied the background from Rob at VidIQ, not from Tech Ingredients. Alec's IKEA shelves are a nice tasteful brown and his lighting's better and he has great hair.

AIMEE, my artificially intelligent machining and engineering expert system is a little chastened from being roasted after getting a bit hyper-critical about how rubbish I am at everything in the RADIX 3D antenna lens video, and is trying to be more helpful. Spoiler alert: it's not going well.

[MachiningandMicrowaves]

For those who have asked, Pierre de Fermat wrote a note about having a wonderful proof of a thing, but the margin of the book he was defacing didn't have enough space. He wrote it in the margin of his copy of Diophantus's "Arithmetica", perhaps in 1637. There's a reference to the margin note in the 1670 edition from Fermat's son saying:

"Cubum autem in duos cubos, aut quadrato quadratum et generaliter nullam in infinitum ultra quadratum potestatem in duos eiusdem nominis fas est dividere cuius rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet."

which my grasp of schoolboy Latin almost renders understandable. My esteemed friend Google Translate refuses to do it on my phone, but typing it in results in:

"Now it is right to divide a cube into two cubes, or a quadratoquadra, and in general no power to infinity beyond the square into two of the same name, of which fact I discovered a wonderful demonstration of course.

THE SMALLNESS OF THE MARGIN WOULD NOT TAKE IT"


Also, I didn't go into how the demodulation works. I need to cover that in detail another time, but it goes a little something like this:

If you have a diode in its square-law region, the current is proportion to the voltage squared. If you then drive it with a mixture of a pure tone at 1 GHz and the modulated signal, then feed the output into a resistor, the voltage across that resistor is the sum of the tone and signal, all squared. The tone is just B*cos(omega*t + phi) and the modulated signal resulting from a simple audio tone is the usual AM expression A*sin(omega t)+ 0.5Am(sin(2pi(fc+fm)t+theta + sin()2pi(fc-fm)t-theta)
omega is just shorthand for 2pi*fc, fc is the 1 GHz carrier frequency and fm is the audio modulation frequency. A and B are just the amplitudes and m is the modulation index (0.05 or so) Now add the two together and square the result using the diode transfer function. You get an exciting mixture of results! After a load of trigonometric identities and wrangling, there are some components with sin(2pi*fc+phase angle) plus a load of other stuff. Run the combination through a diplexer to take anything higher than 3 kHz into a dump resistor and everything below 3 kHz but above 200 Hz into an audio amplifier, and you recover the original audio signal. If there is also some phase modulation, that results in multiple additional sidebands around the 1 GHz carrier, although at a low modulation index, the result is pretty much the same as AM. At higher modulation indices, the results are more complex, with Bessel functions of different orders causing a spread of sidebands rather like in FM. However, they are mostly removed by the low pass filter, except for the low frequency parts of the higher-order sidebands. The amount of phase mod is (luckily) quite low. I hope you can see why I rather glossed over THAT lot, but it would be fun to do a ten minute vid about it at some point, to exercise my MATLAB, Manim, MathCAD and storytelling skills!

[maxtroy]

I didn’t even know something like this was possible without active circuitry. A purely mechanical microphone with no on board power source that can “transmit” wirelessly is just mind blowing. The ingenuity is incredible

[dakel]

Can never get over how much an absolute genius Theremin was. Been interested in the Thing for years, and absolutely delighted by these videos.

[SamwiseOutdoors]

"64 teeth per banana" is the most accurate description of what life is like in an Imperial system that I've ever heard.

[tylerduncan]

This is my first time watching one of your videos and the amount of references and jokes you manage to fit in while still being entertaining and informative is absolutely insane. Good job. You got a new subscription.

[edgeeffect]

Having chopped up a great many microwave ovens, I can definitely assert that resonant cavities are nothing but plain and simple black magic! This series is rather fascinating... my understanding is still only growing with the tiniest of baby steps. But your delivery is keeping me intrigued.

[YorkshirePirate]

I passed my foundation ham exam today, but I was NOT ready for the intensity of science about to be dropped on me in this video. I feel thoroughly inadequate, but I shall keep endeavouring to understand everything after your introduction.

[ferrumignis]

I suspect the pressure equalising hole would have been even more important for atmospheric pressure changes that could otherwise cause a significant shift in resonant frequency, or even cause the diaphragm to push up against the centre pillar in the resonator and stop any modulation. In fact just getting the resonator assembled might be impossible without damaging the diaphragm from overpressure.

[jonnyreverb]

Wow... A passive bug powered like an RF inventory control device in 1945... If they'd pattened it, they could be rich.

[ColinDyckes]

I'd never heard of this 'passive' bug but what an ingenious device and perfect explanation of the LC operation!

[nicku]

I read about it in a book by Peter Wright a good 30 years ago. There was also a description of another high tech magic - locating Russian spies by identifying them by overloading the hetordinates in their receivers with the signal transmitted from counterintelligence cars from the street. If this overload created a dip in the frequency suspected to be spy transmission, agents had confirmation that someone in the building was listening to spy transmissions. It did not require any mechanical operations, however, it was purely electronic manipulation.

[RSGill]

Thank you SO much for these eye-opening videos. I did not know of this until you brought it to my attention. I find the ingenuity behind such simple yet effective devices amazing.

[haph]

"I have a wonderful mathematical proof for that, but this margin is too narrow to contain it"
Ahh, yes, a quality reference sir. You are a man of taste.

[drewcagno]

I understood exactly 0% of what you were talking about, but it's really interesting that you understand it. Lol. Hope you're having a fantastic Easter.

[jjoonathan]

I've always wanted to deep dive the Great Seal Bug but never got around to it, thanks for the explainer! Also -- I think I see a familiar directional bridge on the shelf behind you!

[Logarithm]

the fact that i understood a fraction of that is a testament to how well you've broken up the complexity of it into nice digestible chunks.

[bschneidez]

"I have a wonderful mathematical proof of that but these margins are too small to contain it." I'm dying. Haven't thought about that in sooo long

[michaelbauers]

As I have some very slight knowledge of some of these topics, I slightly understood this. Fascinating. You deserve a lot of views for trying to explain something very technical with enough detail that the interested person with a bit of physics/electronics knowledge can follow it.

[nosenseofhumor]

The Fermat margin joke really got me lol, good one

[SteveCalamia]

This level of technical elegance is oft overlooked in modern times and is absolutely necessary for the next stages in computing. Thank you for sharing this extremely interesting and scientifically _sound_ knowledge!