GPS jamming.

B

binch

Well-Known Member
Joined
3 Jul 2008
Messages
585
Location
gradually diminishing with age. Now Europe
Visit site
Various authorities are beginning to worry about the amount of GPS jamming. At our level this is usually due to lorry drivers not wanting the boss to know where they are, or to car thieves not wanting to be traced, but there are also cases of deliberate jammming of GPS at sea, most notable case being a teenager who was doing it to see if he could. Well he could. Give the little wsotb a job for God's sake.
What interests me as a FRIN is whether anybody has convincing experience of having GPS jammed.
 
I suppose this is anecdotal rather than "proof"

several times going up the Tamar past HM Dockyard Devonport, the GPS lost tracking

it also lost tracking close to a RN Destroyer off the south close


This is the only time I've ever seen it happen
 
Couple of weeks ago at 0400hrs the GPS suddenly showed altitude of -3600 feet then requested a reboot. This happened twice. Then it was fine. On looking at the chart I discovered it was a submarine exercise area south of Eddystone. When I mentioned it at the marina I was told that it was a frequent occurence off Plymouth.
It certainly has never happened to me before.
 
Had it happen once afew years ago in Firth of Clyde during a NATO exercise.Stupidly impossible readings of LAT /LONG----then when that sorted itself out it was fine,except when I later it had jumped by 8000 miles.I can only assumeit thought it had gone to all these places. Rubbish in / rubbish out?
 
The US 'Navstar/GPS' system is, and always has been, a military resource developed to provide tracking and targeting facilities for inter alia Tomahawk cruise missiles. It takes little imagination to realise that many countries would seek to develop 'denial counter-measures', and there is a significant industry in such technologies.

One should not be surprised to hear that just about every RN and RFA ship - as well as those of many other nations - has had the capability for years to interfere with the GPS signal - by one means or another - in their immediate vicinity, and so deny that aspect of terminal guidance to hostile autonomous sea-skimming weapons.

And every system fitted - each of the 'black box' components - needs to be tested from time to time, and each operator needs to be exercised and 'checked out' as proficient at regular intervals. Equally, those defence contractors who make such kit also need to test their prototypes and their production runs. It comes as no surprise that, from time to time, a spurious signal is received by yotties which is displayed as 'garbage output'.

:cool:
 
Military

Yes, they do have countermeasures. But in fact GPS will be phased out for warlike military use soon, if it has not already happened.
They will use "cold atoms, pseudolites, and image aided inertial navigators using laser radar. . . ." whatever that means. (Quote U.S. Chief of Staff at a recent lecture.)
No No No!!!. I am not going to learn that sort of ordure at my age. N, NxE, NNE, NExN, NE, NExE, bubledy bubbledy bubbledy. God's sake give me a large gin.
 
binch said:
Yes, they do have countermeasures. But in fact GPS will be phased out for warlike military use soon, if it has not already happened.
They will use "cold atoms, pseudolites, and image aided inertial navigators using laser radar. . . ." whatever that means. (Quote U.S. Chief of Staff at a recent lecture.)
No No No!!!. I am not going to learn that sort of ordure at my age. N, NxE, NNE, NExN, NE, NExE, bubledy bubbledy bubbledy. God's sake give me a large gin.
Click to expand...

What about nor' nor' east by east a half east?

My smileys have died again---
 
ancientsailor said:
I suppose this is anecdotal rather than "proof"

several times going up the Tamar past HM Dockyard Devonport, the GPS lost tracking

it also lost tracking close to a RN Destroyer off the south close


This is the only time I've ever seen it happen
Click to expand...

I had exactly this problem while sailing past Devenport. I am told by someone who spent his working life on military radars that they could interfere with the GPS signal but whether that was the case then I don't know.
 
it's very easy to do, with just a little knowhow. GPS signals are very weak, they come from satellites, which is the thing most people forget, and easy to over power from a local source.

I'd hope that much like internet viruses, that the vast majority, and the few that really understand, will do what they can, to stop any malevolent interference to what people take for granted
 
Ludd said:
What about nor' nor' east by east a half east?

My smileys have died again---
Click to expand...

Smiley's people?

smileys.jpg
 
simon14b said:
I had exactly this problem while sailing past Devenport. I am told by someone who spent his working life on military radars that they could interfere with the GPS signal but whether that was the case then I don't know.
Click to expand...

I know of two places where GPS in gliders fails: over the French ULF submarine communications antennae near Poitiers and within a mile or so of the big TV transmitter aerial on the Mendips. The latter is unintentional, I'm sure - the former maybe not, since my audio variometer started playing military music at me there ...
 
Confusion

I have persevered in wading through the summary of the international conference on electronic aids. I can't help thinking that I have forgotten how to navigate.
Augmented Reality. When the circular track you are unwittedly on leads you to ram yourself up your own transom.
And what are androids doing at sea?
We'll be having druids next.
But the problem lies in Abbreviations. You only have to go to sleep for a full night and someone has coined at least fifty new acronyms. And then nobody from then on writes in English any more.
Does anybody know who these are?
IMarEST
EEZING
And the following, which were all in the same paragraph
CTO, CTA, 4D, ATFM, SESAR, KPA, CDM and SWIM.
(They involve aircraft )
[I like SESAR. I'm sure it comes from the following
EDCD goldfish
MNO goldfish
SAR
OICAR.]
Nowadays we have navigation by compass,
Navigation by Rhumb line
Astronomical navigation.
and now, navigation by acronym
 
deliberate or accidental?

simon14b said:
I had exactly this problem while sailing past Devenport. I am told by someone who spent his working life on military radars that they could interfere with the GPS signal but whether that was the case then I don't know.
Click to expand...

This is quite true. Radio receivers, although tuned to one frequency (or band of frequencies to be more precise), are not perfect. They cannot reject entirely signals at other frequencies, and ususally the closer the interferer to the wanted signal the poorer the rejection. GPS sets are no exception, and some old civilian ones are pretty bad, so much so that virtually any strong transmitter nearby will jam them (mostly you pay for what you get). Hence I think many of the experiences people have with ships or dockyards interfering with GPS are not deliberate attempts at jamming, but rather that our sets are not well enough engineered to reject nearby transmitters on other frequencies.


The good news is that because the largest market for GPS chips is now in mobile phones, where the GPS antenna is only a few cm at most from the phone's relatively strong transmitter, the robustness to nearby interfering signals has been much improved recently.

But you have to buy a new set, and even then since most GPS devices sold for navigation have 'active' antennas mounted outside there is often limited or no filtering in front of the first amplifier ('LNA'), so it can be overloaded anyway. We should really press the set manufacturers to specify their "out of band blocking" performance, and reviewers should look at this. The loss of sensitivity induced by inserting a SAW filter in front of the LNA is only about 2dB, whereas modern chip sets have improved sensitivity by much more than enough to compensate for this, and the cost only about 15 pence, so the technolgy is affordable and available now.

Another source of accidental jamming is from in-band interferers. Because the GPS band is rather narrow (1.5742 GHz, +/- ~2 MHz) these are mostly from other GPS sets: some emit quite strong signals right in the middle of the GPS band (due to emissions from their Local Oscillator in 'zero IF' designs), which can then be then picked up by other sets. Unfortunately modern sets, despite my praise above, are sometimes no better than old in this regard becase the search for small size, low power consumption and the use of simple passive antennas has caused design compromises in this area. This should improve in the latest chip sets however since, for reasons I needn't go into, zero IF is not well suited to 3G phones, so the inevtitable LO radiation will move out of band and this problem go away eventually.

Of course there is some deliberate jamming, but I think accidental blocking is more prevalent. I have no experiences of deliberate jamming, and what one can do to mitigate it, which I wish to share.
 
You must log in or register to reply here.

Share this page

Top