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

David I. Emery die at dieconsulting.com
Tue Oct 8 01:37:23 EDT 2013


On Mon, Oct 07, 2013 at 11:30:57PM -0500, Bill Hawkins wrote:
> In general, we expect a jammer to be involved in criminal activity.
> 
> What about a wilderness guide whose reputation is built on finding
> the best spots to view Nature's wonders. Should he or she be happy
> to let people in the guided group save the coordinates of those
> spots in order to compete with the guide or avoid guide's services
> in the future?
> 
> Or would that be a justifiable use of jamming?

	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 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."



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