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

jerryfi jerryfi_99 at yahoo.com
Thu Feb 9 06:29:14 UTC 2012


I'm not completely convinced that DTV has been eliminated as a source, but it would take some study (and discussions with the DTV providers).  There may be something there.   The problem you have is that so many (most, if not all) stable rf signal sources are derived from GPS today, so that in the EXTREMELY unlikely event that all (24+) GPS sats went off the air, many of those sources would all be affected to one degree or another.  You might look at the Russian Glonass system, the European Gallileo system (which is only in prototyping stage), and possibly the Chinese Beidou NAVSATS.  Gallileo and Glonass work similar to GPS, but Beidou is a different beast.  There are receivers that use both GPS and GLONASS, but I don't have any direct experience with them.


WWV (and related HF time signal sources) are an obvious alternative source.  NIST operates WWV transmitters at 2.5, 5, 10, 15 and 20 MHz from Fort Collins, CO, and WWVH from Hawaii.  These signals are locked to Cs standards.  There are other HF time signals  from Canada, etc, you might check out.  


Depending on what you want to do, you might just consider synchronizing a Rb, or a bank of Rb's to GPS. Then if GPS went away, the Rb's would free run for a considerable time.  "Considerable" needs to be defined by your timing requirements, and duration, in the non-GPS environment. And then, of course, there are Cesium standards available, if you have deep pockets.


Jerry Finn

AG6HH




________________________________
 From: Chris Albertson <albertson.chris at gmail.com>
To: jerryfi <jerryfi_99 at yahoo.com>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Wednesday, February 8, 2012 9:13 PM
Subject: Re: [time-nuts] Using digital broadcast TV for timing?
 
On Wed, Feb 8, 2012 at 7:48 PM, jerryfi <jerryfi_99 at yahoo.com> wrote:
> Thanks Paul.  You and Bob Camp provided some good updates/info.  It may present enough of a challenge/reward for someone to examine further.  I'm with you on the available time front - too many other projects/commitments to pursue further myself.  I'll be interested if Chris, or someone else, can make some headway though.


OK if not DTV what other common signal that you could pick up without
use of exotic equipment (so this entirely eliminates rotating neutron
starts or "pulsars") what else can you get that has decent timing
other then GPS and CDMA.   I'm not giving up on DTV yet.  The video
signal is compressed so it may be basically white noise but I bet it
is wrapped in some transport like packets that are regular.

In practice GPS works well but a question came up here "What could you
use if GPS went away?"    I said "I bet there is some signal all
around us that just happens to have precision timing embedded in it.
Maybe DTV maybe it's direct broadcast TV.
--

Chris Albertson
Redondo Beach, California


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