[time-nuts] New GNSS chipsets

Magnus Danielson magnus at rubidium.dyndns.org
Mon Apr 2 05:30:53 EDT 2018


Hi Hal,

On 04/02/2018 03:47 AM, Hal Murray wrote:
> 
> magnus at rubidium.dyndns.org said:
>> 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



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