[time-nuts] US considers shutting down Loran

[Hal Murray]

>From http://www.fcw.com/article97298-01-08-07-Web

> Norman said the Alliance for Telecommunications Industry Solutions
> (ATIS), whose membership includes all the telecom carriers in the
> country and equipment vendors, views eLoran as the "only viable
> alternative to GPS for providing [Coordinated Universal Time] of day
> and frequency accuracy that is suitable for a telecom primary
> reference source."

How good is Loran for timing?  What's the right parameter for "good"?


My straw man is that the parameter(or one of them) is the time constant on 
the PLL filter and that Loran would have delays that vary by the time-of-day. 
 (Maybe ground wave avoids that?)  So I'd expect Loran would be OK if you had 
a Rubidium clock and could average over several days.

It might work OK as long as everybody does the same thing.


Why don't cell phone towers get their time from nearby towers and/or their 
land-lines?

In general, chaining PLLs is asking for troubles.  I think there are two 
cases that work well.  One is where the second PLL has a wide bandwidth so it 
can track the first one.  The other is where the second PLL has a low 
bandwidth so it can filter out the noise from the first one.  Either gets 
ugly if you have a long chain.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.