[time-nuts] Low cost synchronization

Magnus Danielson cfmd at bredband.net
Thu Aug 18 20:15:47 EDT 2005

From: Mike Ciholas <mikec at ciholas.com>
Subject: [time-nuts] Low cost synchronization
Date: Thu, 18 Aug 2005 12:29:40 -0500 (CDT)
Message-ID: <Pine.LNX.4.63.0508181135520.24373 at piano.ciholas.com>

Hi Mike,

> 4. GPS Time Receiver
> This is fantasy land.  I don't need the 100ns time reference, all 
> I need is something good to one second or so.  In this case, it 
> seems possible to receive only 1 satellite, decode the digital 
> data, and extract the time.  It would be off by the variation in 
> pseudo range which can't be corrected for.  But I don't care 
> about that level of accuracy.
> The question is, if you don't have to track multiple satellites 
> and don't need to recover the pseudo range accurately, can you 
> build a wickedly cheaper GPS time receiver?  My expectation is no.  
> You probably can get down to maybe half if you are very diligent, 
> which still puts me out of the budget plus has a ridiculous high 
> NRE.  Unless this already exists, anyone?

I have some VHDL code lying around... but no, I think it will effectively be hard to beat
the integration level of modern receivers. The E911 work as well as wish for small
portable receivers has forced integration to go further. On principle of doing a single-
receiver GPS that will work. The first line of analogue receivers where 1-channel
receivers multiplexing between satelites. Checkout the GPS chips again.

> 5. Cellular
> We've done extensive work with embedded cell phone modules.  
> These modules are most often used for wireless remote monitoring 
> and transport digital data.  They do get the time from the cell 
> system.
> Again, cost is a major issue.  An OEM cell module runs over $65 
> in qty so this idea is sunk.  It would also suffer from lack of 
> global and local coverage.

It is a shifting buissness and in longterm you may be toast.

> 6. TV Stations
> TV stations broadcast a time signal that VCRs/DVRs use for clock 
> setting.
> Again, lack of global or even regional coverage.  Some TV 
> stations, annoyingly, broadcast the wrong time, too.  Cost is 
> probably high, but this idea was rejected before this was 
> investigated.

Also, the analogue signal is hitting the deck as ATSC and DVB enters. Sad but true.
However, if you listen to ATSC or DVB pilot-tones ;O)

> 7. Atomic Reference
> Still research, but NIST has a small scale atomic reference:
> http://www.nist.gov/public_affairs/releases/miniclock.htm
> Unfortunately, not ready for commercial apps, probably will be 
> too expensive, and it uses too much power.  The best I could do 
> on power is to power it up periodically and adjust the local 
> crystal to it which integrates long term error.

Small physics package does not say anything about the electronics package ;O)


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