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

[David I. Emery]

On Mon, Oct 07, 2013 at 08:02:13AM -0700, Jim Lux wrote:
> On 10/7/13 7:46 AM, Collins, Graham wrote:

> >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.

	This is also rather a sin of the marketing driven "innovation"
economy - product life cycles are so terribly short that by the time
someone spots a device that can be re-purposed in an interesting way it
is usually already EOL and unavailable in traditional new product
channels.

	It takes time to do the reverse engineering (schematics, source
code, FPGA VHDL - what is that and why should we give it to you ?)  and
time to figure out how to re-purpose and make the thing work and usually
this is part time and one or two people and not a whole staff.  And then
there is time to write it up and publish articles and plans, and time
for folks to try it and discover it works...

	But as many on this list know all too well, even in reasonably
well funded new product development the old story is "hey that is a
really neat chip that does just what I need" only to hear "Sorry too low
demand, or design or production problems, or ROHS or something, not
available in the future - or maybe just vaporware to assess interest and
never really available".   Or you design it in, the company is bought by
someone else, the chip abandoned and now YOUR product is EOL early.

> 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.

	But that is not all bad, if you just need a modem that works.
Choosing something state of the art that DID NOT become a major defacto
standard (and there are dozens of examples in the modem world alone) 
means you only can expect to use the original device and maybe one or
two subsequent versions before it becomes unavailable and completely
obscure and rare and totally incompatible.   And then your design has to
be incompatibly upgraded with no backwards interoperability support
where if you had used some moldy oldy but goody you probably could buy
modern DSP based hardware that does that standard (you can for 202s)
among many other useful ones...and support both higher performance
and backwards compatibility modes at low cost and with high performance.

	Obviously the problem then becomes convincing enough old pharte
holdouts to upgrade when it truly becomes a nightmare to support the old.
And that is not always easy.

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."