[time-nuts] How hard is it to detect a GPS Jammer?

[Jim Lux]

On 10/7/13 7:46 AM, Collins, Graham wrote:
>
> Indeed, the inexpensive DVB-T dongles are showing up in many places
> including as David noted, decoding GPS.
>
>
> The AMSAT Fun Cube Dongle is a very capable and interesting device.
> Interestingly it uses the same Elonics E4000 front end chip that many
> of the inexpensive DVB-T devices do. Apparently Elonics is no longer
> in business and the inexpensive DVB-T devices using this chip are
> becoming less common. The DVB-T devises using the R820T chip are
> becoming the preferable versions when those with the E4000 cannot be
> found. I wonder if the Fun Cube Dongle will be likewise changed
> (perhaps it already has).
>

This illustrates is the fundamental problem with leveraging cheap 
consumer or government surplus gear.  The hacker community moves much 
slower than the commercial one, so you wind up with projects requiring 
things that are no longer sold.  It's particularly endemic in the 
amateur radio community where we are always repurposing something that 
hasn't been made for 30 years.  But it makes it hard for the new 
entrant, who doesn't have a box full of old MASTR-II VHF radios or Bell 
202 modems or whatever sitting around.

But the existence of that gear in some folks's garages tends to ossify 
the development.  How many Bell 202 modems are still in use? But VHF 
packet radio is 202 compatible, because every product made for the last 
30 years was compatible with the 202.  Not because it's inherently good, 
but because you want to be compatible with the other people, and there's 
a sort of rolling compatibility.

(Amateur radio is not the only instance of this. The Scientific 
Spaceflight community is the same.  We love to use spares from previous 
missions to reduce costs, but that brings along the need to be 
compatible with the interfaces of those spares.  As a result, 
MIL-STD-1553B Notice 2 or Notice 4 is still used on spacecraft, even if 
it's not the most appropriate, lowest power, etc.)


For a particularly interesting example, look at the plethora of versions 
of the WRT-54G WiFi router popular with hackers; there's about 50 
versions listed on the DD-WRt website.  Some of he versions  are 
amenable to dropping in a new OS and/or software, others are not, and 
still others are "modifiable" (as in cutting traces, soldering, adding 
parts and/or connectors) to put in new software.