Re: [time-nuts] New GNSS chipsets
I have advocated for receivers able to handle multiple frequencies and
multiple GNSS for some time, sneaking it into documents, so there should be
some preparations for this now.
How well do various GNSS track UTC and/or eachother?
The benefit is naturally redundancy, but also higher precision.
I've been assuming the cheap GPS jammers will kill the others too. Are there
any signals far enough away from L1 that they might get through?
--
These are my opinions. I hate spam.
Hi Hal,
On 04/02/2018 03:47 AM, Hal Murray wrote:
I have advocated for receivers able to handle multiple frequencies and
multiple GNSS for some time, sneaking it into documents, so there should be
some preparations for this now.
How well do various GNSS track UTC and/or eachother?
Within a handful of ns from UTC, which is quite good.
GPS masterclock is to be held with +/- 1 us of UTC USNO, but in practice
it is held much tighter, as within 3-5 ns or so. I expect the other
constellations to be in that neighborhood even if not with that low
value. It should be easy to check, but I'm a bit lazy to do so right now.
The benefit is naturally redundancy, but also higher precision.
I've been assuming the cheap GPS jammers will kill the others too. Are there
any signals far enough away from L1 that they might get through?
The cheap jammers hit L1 C/A. It takes more jammer-cores to cover more
frequencies, and the more frequencies you track, the harder to pinpoint
them all, and well, until full constellation full frequency receivers is
common, jammers will not adapt fully to it.
How well antennas and receivers handle sideband jamming depends on the
receiver design, just as in normal radio setups.
Cheers,
Magnus
Hi
On Apr 1, 2018, at 9:47 PM, Hal Murray hmurray@megapathdsl.net wrote:
I have advocated for receivers able to handle multiple frequencies and
multiple GNSS for some time, sneaking it into documents, so there should be
some preparations for this now.
How well do various GNSS track UTC and/or eachother?
These days Glonass puts out an offset number that should be good to the single
digit nanoseconds (unless it’s broke). The Europeans have set up to effectively stay
“as close as you can get” to sync. Right now those are the only three that are likely
candidates for time sources.
The benefit is naturally redundancy, but also higher precision.
I've been assuming the cheap GPS jammers will kill the others too.
Maybe not. Glonass is not on quite the same frequencies. The signal formats of
each system are very different. A jammer that nukes one may not have any
impact on the rest. Indeed a megawatt level broadband DC to light jammer
would take out a lot of things. It’s also a pretty easy item to track down.
Straight broadband jamming should simply shut a receiver down. That’s why
GPSDO’s go into holdover (and why you have GPSDO’s). Are all receivers ever
made perfect in the face of any and all crud … maybe not.
The bigger issue is a “spoof” signal that deliberately tricks the receiver into thinking
it is locked to legitimate satellites. There are ways to do that. Receivers are not
going to reject that solution and away you go. Doing a working spoof for multiple
systems …. much harder than a single system.
Bob
Are there
any signals far enough away from L1 that they might get through?
--
These are my opinions. I hate spam.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.