[ntp:questions] does this make sense?

Terje Mathisen terje.mathisen at tmsw.no
Fri Apr 6 10:02:12 UTC 2018


William Unruh wrote:
> On 2018-04-05, Terje Mathisen <terje.mathisen at tmsw.no> wrote:
>> I've designed similar setups a couple of times: Since we're located
>> in Europe my backup was the German radio transmitter since that one
>> uses spread spectrum modulation of the carrier, enabling 10-15 us
>> precision.
>
> That is about 2 miles light travel time. I suspect you are further
> than that from the tranmitter. And propagation is all in the
> atmosphere, and the speed of radio  varies in the atmosphere,
> depending on the pressure, the humidity, clouds,.... Ie, I am
> doubting the 10-15us. Maybe 10-15 ms.?

Bill, please!

This was of course with an initial propagation time measurement period, 
where we used the GPS PPS signal to verify the ground wave propagation 
time of the radio signal, then adjusting for that offset in the radio 
driver.

Yes, propagation time will vary a bit over a 24H period, but this 
provides a very useful backup.

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"



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