[time-nuts] Using digital broadcast TV for timing?

Bob Camp lists at rtty.us
Wed Feb 8 17:05:34 UTC 2012


Hi

Back in the late 90's Symmetricom made up some disciplined Rubidium's that
ran off of cell towers. If you Google Timesource 2700 you can probably find
a lot of information on them. Until people figured out what was in them,
they were a great way to score a PRS-10 Rubidium (great phase noise) for
very little money ($200 or so). 

The telcom companies used them for a while and ultimately scrapped a lot of
them out. Rumor is that not all cell towers are as locked up time wise as
they should be. The discipline obviously only works if they are.

Even if you have a good tower today, there is no guarantee that it's locked
tomorrow.  GPS can drop out due to equipment issues and you will drift as
the tower drifts. 

Bottom line, it's a solution that brings in a whole new set of problems.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Hal Murray
Sent: Wednesday, February 08, 2012 6:01 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Using digital broadcast TV for timing?

> Maybe cell site transmissions are better?

At least one company makes them.

http://tinyurl.com/72j5e6n
http://www.endruntechnologies.com/telecom-primary-reference-source.htm

It's CDMA.  I don't know much about cell phones, but I think that's the old 
protocol that will probably/eventually fade away.

I don't know anybody who has worked with them.  The advantage is that you
can 
set them up in your machine room and don't need an outside antenna.  (If
your 
cell phone works there, this should work too.)

I'd expect the time accuracy would be not as good as GPS.  It would be off
by 
the time-of-flight from the cell tower, 5 microseconds per mile.  That's 5 
microseconds per mile which is no problems unless you are a time-nut.  (I 
don't know if the cell towers add more to that.)


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




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