[time-nuts] Effects of Simple GPS jamming on GPSDO's ?

Scott McGrath scmcgrath at gmail.com
Fri Aug 31 19:02:31 EDT 2018


That’s the scenario i’m most concerned with not war or terrorism but a natural event which has occurred before and will occur again.

Rebooting technology will be a heck of a lot easier with a variety of precision time/frequency distribution methods.

After a Carrington type event a working Cs or Rb will be worth several times their weight in gold.

Its not that I’m nostalgic for the old days but having a HF frequency source will allow HF networks to determine propagation .

Content by Scott
Typos by Siri

On Aug 31, 2018, at 6:38 PM, Dana Whitlow <k8yumdoober at gmail.com> wrote:

I'm thinking about if/when "the big one hits" and takes out most or all of
the GPS
sats, cell phone systems, etc.

Then the time required to reboot up to a reasonable level of technology
might turn
out to be limited by our ability to determine time and freq somewhat
accurately.  The
better we can do from scratch, the faster the reboot.

So one question is:  how many Cs beam clocks are out there which are kept
running
and "on time", at least by frequent logging of errors if not by actual
setting/tweaking?

If "the big one" is global nuclear war, of course we'll all have far more
to worry about
than keeping our watches accurately set.  But what if it's another
Carrington-level
event?  I'm sure we'd all like to get back to business as usual as quickly
as possible.

Dana


> On Fri, Aug 31, 2018 at 5:23 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> I think we have a little bit of confusion here. WWVB is not going to help
> anybody navigate.
> It’s not going to help track people with ankle bracelets or trucks
> stopping at bars. Car thieves
> jamming Lojack still happens. Turn iWWVB on or off, this stuff still goes
> on. None of this is
> a Time Nuts sort of issue.
> 
> The only thing WWVB *might* do is provide timing. That’s very different
> than navigation. A
> mobile this or that driving by puts your GPSDO into holdover. It maintains
> time while it is in
> holdover. Minutes or hours, possibly days … works the same way. The system
> keeps running
> just like GPS was doing fine. If after a day or more, the GPS is still
> jammed, that single  cell tower
> shuts down. Take out one cell tower and the system keeps running. There is
> a lot of overlap on
> these systems. Towers go down a lot more often than you might think …..
> 
> Do all systems work identically in terms of timing? Of course not. If
> timing is critical to operation,
> systems do use GPSDO’s. The same basic principles apply. The main question
> would be one
> of overlap between elements of the system.
> 
> The same jamming that takes out GPS for timing also takes it out for
> normal navigation. Take
> it out over an entire city and everybody’s vehicle navigation system goes
> out. Do that even for
> a couple of hours and it’s on the evening news. Do that for a day and
> there *is* a response.
> That’s the kind of thing needed to impact utility systems (like cell
> towers) in a significant way.
> It simply does not happen ….City wide is very hard to do from the ground.
> From the air, you
> can get the coverage. It’s tough to keep doing it from the air for days on
> end.
> 
> So, interns of “the world ends if / when WWVB turns off” … not so much.
> 
> In terms of the initial question, GPSDO’s in general are pretty good at
> handling the typical
> jamming they might run into.
> 
> Bob
> 
> 
> 
>> On Aug 31, 2018, at 3:52 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
>> 
>> And here is one of the schematics running around the ‘net.   This one is
> noise based
>> 
>> <image1.png>
>> 
>> 
>> 
>> On Aug 31, 2018, at 3:41 PM, Gerhard Hoffmann <dk4xp at arcor.de> wrote:
>> 
>> 
>> 
>>>> Am 31.08.2018 um 19:39 schrieb jimlux:
>>>> On 8/31/18 10:15 AM, Bob kb8tq wrote:
>>>> Hi
>>>> 
>>>> Having spent a lot of my life designing GPSDO’s it’s a “that depends”
> sort of thing.
>>>> For a simple noise jammer, yes, they pretty much all will go into
> holdover. When the
>>>> jammer goes away, they come out of holdover. There are a few older
> units that may not
>>>> do quite as well with various sorts of broadband jamming.  With a
> spoofing jammer that is flying
>>>> around overhead and simulating an entire constellation … you could see
> any of them do odd
>>>> things. An airborne jammer flying over this or that city likely gets
> you into a “act of war” sort of issue.
>>>> It’s something you build if you are a nation state.
>>>> 
>>>> The performance with noise jammers is not a guess. It’s based on field
> experience and
>>>> all those never ending meetings I keep referring to …..
>>>> 
>> IIRC, there was a truck driver who successfully jammed all those
> airworthy GPS systems
>> at SF airport trying to hide his private detours, just by passing on the
> highway with
>> El Cheapo hardware.
>> 
>>> 
>>> In effect, a broadband jammer (or, probably, a tone jammer that
> overwhelms the 1 bit ADC receiver) is the same as a "loss of signal" - the
> receiver probably doesn't know the difference - it just drops sync and
> tries to unsuccessfully reacquire.
>> 
>> I think that Holmes wrote somewhere that the easiest way to jam was a
> carrier quite close
>> to the frequency where the suppressed carrier of the BPSK would be. It
> could be weak because
>> it would have some processing gain, even if not completely sync to the
> rest of the signals.
>> The typical 1 or 2 Bit ADC has no chance to see it separated from the
> rest.
>> 
>>> 
>>> So you can test your hold over behavior with aluminum foil (or your
> hand) over your antenna<grin>
>>> 
>> OMG, I first read "with aluminium foil hat over your head"....
>> 
>> Cheers,
>> Gerhard
>> 
>> 
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