
GBPPR Non-Linear Junction Detector - lainon
https://web.archive.org/web/20130718061802/http://servv89pn0aj.sn.sourcedns.com:80/~gbpprorg/mil/non/
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PhantomGremlin
One of the great stories of using "Non-Linear Junction" devices occurred circa
1985, during the Cold War between the US and the Soviet Union.

The US was building a new embassy in Moscow. Naively, they allowed the Soviets
to do most of the work. The result was a building impossible to secure.
Eventually the top 4 stories needed to be completely replaced.[1]

The relevant part to this discussion is that the Soviets mixed thousands of
discrete diodes[2] into the precast concrete. What is a diode? A nonlinear
junction. What does it cost? A few pennies. What does it do? It creates false
positives, so it keeps you from using a device such as the one discussed in
this article to detect actual bugs.

[1]
[https://en.wikipedia.org/wiki/Embassy_of_the_United_States,_...](https://en.wikipedia.org/wiki/Embassy_of_the_United_States,_Moscow#Building)
[2][https://www.washingtonpost.com/archive/politics/1990/06/18/u...](https://www.washingtonpost.com/archive/politics/1990/06/18/unbeatable-
bugs-the-moscow-embassy-
fiasco/5bb6dcbf-0a61-4948-a953-e2d81085ed05/?noredirect=on)

~~~
userbinator
The USSR was extremely skilled at creating listening devices that didn't have
nonlinear junctions, or indeed any active electronics at all:

[https://en.wikipedia.org/wiki/The_Thing_(listening_device)](https://en.wikipedia.org/wiki/The_Thing_\(listening_device\))

~~~
CamperBob2
Yes, that's a famous one. I got a chuckle out of the photos of Pelosi and
Schumer leaving the White House after meeting with Trump a while back (
[https://twitter.com/cbouzy/status/1072563584796909568](https://twitter.com/cbouzy/status/1072563584796909568)
). It's as if the Russians aren't even trying to hide their bugs anymore.

~~~
hatsunearu
What's going on in that picture?

~~~
CamperBob2
I don't know if you're up to speed with US politics, but at the time the photo
was taken, they were the Congressional minority leaders. They had just told
the President that they wouldn't support funding for his border wall project:

[https://www.realclearpolitics.com/video/2018/12/11/trump_mee...](https://www.realclearpolitics.com/video/2018/12/11/trump_meets_pelosi_and_schumer_the_wall_is_getting_built_one_way_or_another.html)

The President insisted on debating the issue with them with the press in
attendance, which is somewhat unusual, and they embarrassed him rather badly
as a result. They are strutting away more or less triumphantly. Whether that
was a good or bad thing isn't a good thing to get into here, but that's
basically the gist of it.

The joke is that the wooden plaque above the front door to the White House
resembles the 'Great Seal' bug that userbinator mentioned. This was an
advanced listening device that the Soviets presented as a gift to the US
ambassador at the end of WWII. It was advanced in the sense that it was
entirely passive, requiring no power or vacuum tubes, and was very hard to
detect with the technology of the day. It could be said to be among the first
applications of modern RFID technology.

~~~
hatsunearu
Ah, the plaque. Thanks.

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na85
Any theory on why PN junctions emit even harmonics and natural nonlinear
junctions emit odd harmonics?

~~~
tlb
A PN junction (ie, a diode) only passes current one way, so a sine wave
applied across a PN junction gets turned into only half a sine wave, with
either the positive or negative half clipped depending on the polarity. The
fourier series of a rectified sine wave is mostly the second harmonic.

A natural nonlinear junction usually consists of a thin layer of insulating
oxide between two pieces of metal. It only conducts when the voltage exceeds
some threshold where the electrons tunnel through the insulator. When a sine
wave is applied, both the tops and bottoms of the waveform are clipped.
Because it's symmetrical around zero, the energy it re-radiates is mostly at
the third harmonic.

~~~
DoctorOetker
does this in only detect junctions _connected to an [explicit or implicit]
antenna_ or does it also detect any junction without the junction needing to
be connected to an antenna?

my intuition is this method would require the detected junction to be
connected to at least an implicit antenna to which the detector can couple,
but I could be wrong?

~~~
CamperBob2
Anything that's more or less conductive can be an antenna if the frequency is
high enough. That's one reason to design these instruments to operate in the
2.4 GHz ISM band, where the wavelength is around 12 centimeters. Junctions
associated with metallic objects over 1 cm in size should be readily
detectable.

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tgsovlerkhgsel
I wonder how much easier/cheaper this would be with modern technology/parts
(archive.org shows that the link to this project on the overview page already
existed in 2008, which is their first capture, and the PCB style looks quite
old).

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avian
It should be noted that this is for US use-only, since it transmits on the 900
MHz band (FCC part 15).

In Europe this frequency falls into the GSM band and will get authorities to
your doorstep in a hurry.

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CamperBob2
Kind of a bummer, doesn't look like we ever find out if his project worked or
not.

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nicklovescode
I read this as “GDPR non-linear function detector” for neural network
regulation

~~~
Kenji
Yeah haha I read GBPRR and thought "Oh no is this another law the EU wants to
introduce?"

~~~
crankylinuxuser
I vouched for this, because I thought exactly the same thing! And wherever
killed it needs to get a sense of humor.

And, I'm giving a talk at CircleCityCon about signals intelligence. One area I
haven't gotten into is NLJDs.... one can only diversify into so many areas :)

Edit: Hmm. an immediate -1. Someone's got an axe to grind.

