
Review and Teardown of a Cheap GPS Jammer - wolframio
http://phasenoise.livejournal.com/2017/11/3185.html
======
exhilaration
The article mentions the incident around Newark Airport where a truck driver
using a GPS jammer was interfering with air traffic. Here's an article from a
local source if you're interested in the details; he was fined $32k:
[http://www.nj.com/news/index.ssf/2013/08/man_fined_32000_for...](http://www.nj.com/news/index.ssf/2013/08/man_fined_32000_for_blocking_newark_airport_tracking_system.html)

~~~
dwyerm
The actual enforcement action notice is at the link below. The FCC does _not_
mess around. They started at $42k, but were 'nice' and offered him a 25%
discount because he voluntarily relinquished the jammer.

[https://apps.fcc.gov/edocs_public/attachmatch/FCC-13-106A1.p...](https://apps.fcc.gov/edocs_public/attachmatch/FCC-13-106A1.pdf)

~~~
wsh
He couldn’t pay it all, so the FCC settled for $2,360, paid in installments:

[https://apps.fcc.gov/edocs_public/attachmatch/DA-16-184A1.pd...](https://apps.fcc.gov/edocs_public/attachmatch/DA-16-184A1.pdf)

~~~
dzhiurgis
Not as bad as healthcare /s

------
Cthulhu_
It doesn't go too far in depth; basically it says it's got a signal generator
and an amplifier and it should work in a 30 meter radius, give or take.

OTOH, short and to the point, nothing wrong with that. It also (importantly)
notes there's no jamming on other frequencies.

~~~
ovi256
There's not much more going on with a physical layer jammer. That's all this
jammer does. It jams the GPS carrier band so that a receiver can't "hear" the
satellites.

You can put together such a jammer from a lab signal generator and a microwave
power amplifier that can cover in the GPS band. You may have to tweak the
signal generator to get a suitable wide signal. GPS is not a narrow, but a
wide-band signal. This helps receivers to reject narrow interference.

------
grdeken
See also: [https://arstechnica.com/information-
technology/2017/11/austr...](https://arstechnica.com/information-
technology/2017/11/australian-man-uses-snack-bags-as-faraday-cage-to-block-
tracking-by-employer/)

------
arca_vorago
GPS jamming is a good way to have men in black show up at your doorstep.
Source: a friend.

~~~
londons_explore
+1 to this.

Men showed up at my doorstep... I removed the designs from github and they
went away happy.

No fine or anything, but it was clear I didn't have a choice...

------
dsfyu404ed
So is anyone making one that emits on all (or some useful subset of) the
frequencies a modern smartphone uses, has a ~30mm range and is powered by the
phone?

The Chinese could crank these out and have the to your door $3.99USD.

~~~
drzaiusapelord
They were selling these online from shady resellers at least ten years ago. A
friend picked one up and told me he could jam some phone calls on the train,
depending on carrier and frequencies used I suppose. I think it broke a week
or two later and he tossed it.

Second link from google:

[http://www.jammerfromchina.com/categories/Mobile_Phone_Jamme...](http://www.jammerfromchina.com/categories/Mobile_Phone_Jammers/)

------
woliveirajr
> When using GPS receivers in city urban canyons with tall buildings, the
> shadowing and multi-path effects results in poor GPS signal reception and
> jammer range can be even hundreds of meters at street level.

That was something that I haven't thought off. The jammer will have less
interference from shadowing and will benefit from reflection of buildings, so
in a city environment it interferes more than in open air.

~~~
olympus
Pretty much. Here's an expanded, but still very simple way to think of the way
this noise jamming works:

\- A GPS receiver needs a signal/noise ratio above X dB to get a lock

\- Higher gain antennas, more sensitive receivers, and higher powered signals
add to the numerator (good)

\- Antennas with smaller sidelobes (often a consequence of a high gain antenna
or nulling antennas), and better signal processing reduce the denominator
(good)

\- There is a pretty good S/N margin when using a modern receiver with a good
antenna in open space

\- Shadowing reduces the signal strength and thus reduces the numerator (bad)

\- Multipath effects increase noise, and thus increases the denominator (bad)

\- Jamming increases noise, and thus increases the denominator (bad)

\- Jamming can be improved by cranking up tx power or using a higher gain
antenna (or both)

\- In open space, a jammer must overcome the entire S/N margin by itself. GPS
systems are so highly optimized (very good algorithms) and have such a big S/N
margin that you can often get a lock just by putting the GPS in a hole and
that nulls enough of the jamming.

\- In a city, shadowing and multipath eat into the S/N margin by quite a bit,
so the jammer doesn't have to do as much. Sometimes the urban environment is
so bad that GPS can't get a lock even without a jammer.

\- Jamming strength decreases with the square of the distance (or 2x when
talking in terms of dB, which are logarithmic)

\- The margin reduction by the shadowing and multipath benefit the effective
distance by the square of the reduction (or 2x when talking in terms of dB)

\- So any natural jamming benefits the jammer by allowing it to operate much
further away or operate at a lower power. There isn't much you can do to
reduce natural jamming like multipath or shadowing other than moving to a
different location.

edit: grr, I hit tab and enter before finishing.

------
Hasz
Would have loved a straight on close up of the board. The PCB routing at high
frequencies is always interesting to see.

~~~
westbywest
You can get a good idea of the signal path to the antenna mounts with the
photo provided, especially the photo visible via the underlying link to
dx.com. Trace width would be set to match desired impedance (e.g. 50Ohm),
generous spacing from adjacent ground plane for isolation, and big radii on
corners to minimize self-capacitance. The 45deg component mounting is unusual,
especially since the equivalent (?) PCB on dx.com doesn't have it. Perhaps
this board was fabbed in low enough volume that optimizing pick & place to
only do multiples of 90deg wasn't needed.

