[time-nuts] Re: What GNSS module to buy for a good time reference?

[Bob Camp]

Hi

The “big deal” with no L2 is fairly simple:

One of the great things about dual freq modules is the ability to send off data
and very quickly get back a corrected version. If you use NRCan, this includes
clock corrections. They are good to the ~ 0.1 ns level. You can get to < 1x10^-14
in less than a day. 

The problem is, the free correction services (at the moment) are L1 / L2 based. 
For whatever reason, they don’t (yet) understand L5. That may change, or it
may not change. Right now, it’s the way it is ….

If you want to go crazy, the Mosaic-T is the best of the best in terms of GNSS
modules at the moment. They apparently are well aware of this and charge
accordingly. You can buy a *lot* of F9T’s for the price of one Mosaic-T. 

Bob

> On Jun 21, 2023, at 10:58 AM, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> On 6/21/23 7:37 AM, John Ackermann N8UR via time-nuts wrote:
>> The F10T looks interesting, but from the datasheet it is missing a few maybe important features compared to the ZED-F9T:
>> 
>> -- L1/L5 bands only (no L2 option)
> 
> 
> I'm not sure no L2 is such a big deal - going forward, people are pushing to L5. It's better protected spectrum management (adjacent user) wise, it has 3dB more power than L1, and longer spreading codes.   The only hiccup is that it's only live on 17-18 satellites, 24 by 2025.  L2 has *less* power than L1, but the longer codes for L2C should make up for that.
> 
> A question would be whether a L1, L2 receiver uses the L2C, or whether they are just doing phase retrieval on the L2 unmodulated carrier (older satellites). Or some sort of codeless processing.
> 
> There's also a somewhat wider spread between L1 and L5, so in theory, you could do better ionospheric corrections.
> 
> L1 - 1575.42
> 
> L2c - 1227.6
> 
> L5 - 1176.45
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