On Mon, Oct 07, 2013 at 08:02:13AM -0700, Jim Lux wrote:

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 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@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."

Yes, these specific jammers do, but someone asked the general question "how
to detect a jammer" and a sophisticated jammer will use no more power than
is requires so as to avoid detection.  Could it be that there are such
devices and they are successful at avoiding detection?    Likely not as at
present no one cares if they are detected.  But if they start getting
hunted out things will change.

About spoofers, yes thay are not available on eBay.  But I was thinking
about military applications.  Can you know when you are being spoofed?

On Mon, Oct 7, 2013 at 6:11 PM, Jim Lux jimlux@earthlink.net wrote:

--

Chris Albertson
Redondo Beach, California

On 10/7/13 9:30 PM, Bill Hawkins wrote:

or the favorite fishing hole..

Way back when, one of the applications of frequency hopping radios was
for fishermen (ocean) so that they couldn't be DFed.  They had already
done the scrambler thing.

No.

It's that same moral thing.. Should you allow cellphone jammers in movie
theaters?

In my mind, these are all hacks to solve a more fundamental social
question about "appropriate use".

cellphone jammers are a sort of passive aggressive way for a business
owner to not have to confront paying customers about their misuse of
cellphones.

At the Athaeneum, the faculty club at CalTech, cellphone use is not
permitted.  Pull out a cellphone, and the staff politely tells you "Sir,
we would prefer you not use that here, would you like to step outside".
At the Austin Drafthouse theater, they're a bit more confrontational.

Anyone can buy a chainsaw or sledge hammer. There is potential for
misuse, but common decency mitigates against those uses.

On Mon, Oct 07, 2013 at 11:30:57PM -0500, Bill Hawkins wrote:

No.

Jamming can potentially impact a much wider area and safety of

life critical uses of GPS, and  very few wilderness guides are expert
enough to understand, control and mitigate this risk.  And even if one
particular one was, how is this to be reliably ensured ? Should  he or
she be licensed and certified and regulated as to how and when he might
jam safely - we don't current issue GPS denial licenses (except maybe to
LightSquared) ?

And even with someone suitably trained and licensed and

certified there is a balance between the slight risk that his jamming
harm something important or critical that society relies upon and his
own personal interest in denying GPS to his customers that I am not sure
we as a society have quite figured out.  Should private businesses be
allowed to deny GPS (or for that matter cellphone access) to folks
nearby or their customers - is this a legitimate interference with a
public resource ?

Obviously if the answer is yes, businesses should be allowed to

jam cellphones or GPS - then what are the limits - eventually all those
private jammers will make such services MUCH less useful - as they will
be unpredictably unreliable at apparently random times and places which
makes it very hard to trust them for anything important.  We will in
other words have allowed the private interests of certain folks to
destroy a commons, something we are getting increasingly good at BTW.

I suppose it is SOMEWHAT justified for a guide to search his

customers for GPSes, or have a strict policy of dropping them off at the
nearest road if they are found to be using one, or even to use a GPS
detector to ID GPSes in use... but an active attack seems wrong given
the risks involved.

And anything more nuanced in a policy on such invites various

low life scumbags to push the limits and use blatantly excessive power,
dangerous antenna locations, and generally horrid engineering that puts
important uses and users of the technology at serious risk for very
selfish personal reasons - perhaps in some cases just buying some cheapo
jammer instead of a proper licensed and limited one managed and
installed by someone who knows what he is doing.

Finally of course, who is to say that I cannot use my cellphone

for important messages - perhaps life critical (my wife is a doctor and
does this from time to time when she is on call)... or my GPS to locate
a store somewhere... perhaps if the jamming ONLY worked in a completely
private space owned or controlled by the jammer and not at all outside
of it would this begin to be marginally acceptable but it certainly
isn't in public spaces.  And I believe there should be mandatory readily
visible notices saying that jamming is use... allowing someone who
truly needs access to know what is happening.

As for the wilderness case specifically there are any number of

strategies to defeat short range jamming of that sort - just announce
you have to "go" as the group leaves the scenic knoll and go back and
take a bearing (maybe automatically from a concealed GPS you already
have in you backpack) while peeing on the special rock...  Inverse
square law applies here of course... hard to radiate enough power to
deny over a long enough distance without being completely unsafe for
other users.

--
Dave Emery N1PRE/AE, die@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."

I for one would insist on complete situational awareness at all times.
The alternative is being LOST.  That can be bad for one's health.

The last time I was willingly lost was when Betty and I were returning
from the Palace Real in Madrid and we decided to just start walking
to the east.  Then there is the Maze at Hampton Court.  Of course we
weren't really lost, but merely in a state of degraded situational
awareness.

On 10/07/2013 09:30 PM, Bill Hawkins wrote:

--
Chuck Forsberg WA7KGX  caf@omen.com  www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc      "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231  503-614-0430

Le 8 oct. 2013 à 10:29, Chuck Forsberg WA7KGX a écrit :

That is not the same as not wanting to be FOUND.

And some of them have considerably higher EIRP,  Like THIS one,  As you
can see they are not sophisticated devices they are intended to swamp the
real GPS signal,

Spoofers would be much harder to detect which is why GNSS systems intended
for military use rely on encrypted signals and fairly sophisticated key
management techniques.

Now for nightmares - the GPS Jammer shown below has an advertised EIRP of
3.4W and the vendor has another with an EIRP of  7.2W

http://hem.passagen.se/communication/gps.html

[image: Inline image 1]

On Mon, Oct 7, 2013 at 9:11 PM, Jim Lux jimlux@earthlink.net wrote:

Hi

But there's obviously something wrong with the 400 KM number.

1. If +10 dbm is good enough to burry a useful signal at that distance, it should be good enough to communicate at that distance. That's pretty impressive QRP without high gain / directional antennas involved.
2. The radios (at least the modern ones) do have CW signal immunity. Weather that's 60 db or something else probably varies with the make / model of the GPS. How well that works with a VCO jammer - again, a that depends sort of thing.
3. There's a (maybe) 40 db variation in GPS signals. To deny service you need to take out the strong ones, not just the weak ones.
4. Even without specific anti-jam in the GPS, the code it's self does have some immunity to a jammer.

Of course you don't have to look very far into the archives to find wonderful examples of slipped decimal points in my posts….

Bob

On Oct 7, 2013, at 9:11 PM, Jim Lux jimlux@earthlink.net wrote:

On 10/8/13 4:17 AM, Bob Camp wrote:

You're right, I forgot the process gain of the despreading.
Assuming you're going from 1 Mchip/sec for the C/A code to 50 bps for
the nav message, that's 43 dB

That alone gets you to 2km jamming range from 400km, but that also
assumes that the jamming signal doesn't inhibit acquiring the code and
despreading.

As Dixon's book on Spread Spectrum says, "acquisition is the hard part";
because you don't have the process gain yet. I suppose with a parallel
acquisition strategy, you're basically trying all codes, and that might
be able to work.

But even so, those sorts of process gain arguments don't necessarily
work if the receiver has a hard limiter or quantizer in it.

I don't know that modern consumer GPSes have CW immunity. If they're
using a 1 or 2 bit quantizer, a strong CW signal pretty much captures
the front end.

Easy to try.  Let me just fire up my kilowatt 1.5 GHz transmitter here<grin>