On 2020-12-09, Martin Gregorie wrote:

> On Wed, 09 Dec 2020 10:35:11 +0000, Adam Funk wrote:
>
>> On 2020-12-07, Martin Gregorie wrote:
>>
>>> On Mon, 07 Dec 2020 15:55:32 +0000, Ahem A Rivet's Shot wrote:
>>>
>>>> On Mon, 07 Dec 2020 14:50:01 +0000 Adam Funk 
>>>> wrote:
>>>>
>>>>> I was just wondering about what kind of situation needs the external
>>>>> clock so the time is accurate *before* NTP starts working.
>>>>
>>>>  It rather depends on how long might elapse before reaching a time
>>>> server, if there's any danger of that being a long time then a RTC is
>>>> very helpful, if you're sure of a time server immediately after boot
>>>> then it's pretty much useless.
>>>
>>> Don't forget that an old GPS unit, provided it has serial NMEA0183
>>> output which many of them had, can be used by ntpd as a primary time
>>> reference. These can be connected to an RPI via a USB-serial adapter.
>>> There is a reference driver for ntpd that allows it to accept an
>>> NMEA0183 primary time stream.
>>
>> (Not that I need something like this, but it's interesting.)
>>
>> I don't think an old GPS unit would be able to get a signal in my
>> "network cupboard", which is a shelf in the back of a wardrobe under the
>> stairs from the 1st to 2nd floors, & not on an outside wall.
>
> The older ones often don't work in a house, and sometimes not in a forest
> either, let alone under a tin roof. Modern receivers are much more
> sensitive. I've just fired two GPS receivers up to prove this point:
>
> - My old (1990) Garmin GPS2+ had no signal at all in the sill of a South-
> facing window and had problems outside it as well, due mainly to the sky
> view being restricted by both the house behind me and (bare) trees on the
> other three sides. It did eventually find two satellites, but never
> determined where it was.
>
> - My more recent (2014) Medion S3747 PNA got enough signal on the window
> sill to set its clock, but couldn't see enough satellites to determine
> its position. However, when it was taken outside to the same point as the
> GPS2+ it was able to determine its location and altitude after around 2
> minutes.

Interesting.  Of course I'm not surprised that the technology has
improved!

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