[time-nuts] (no subject)

Hal Murray hmurray at megapathdsl.net
Sat May 22 07:26:13 UTC 2010

Caveat: I've never worked with a 3805.  I do have a 380.  I'm assuming they 
are close.

> If the gps hasn't been turned on in a while, it will need to download a new
> ephemeris.  With the new ephemeris, it can  find it position much faster
> because it will know pretty close where the satellites are, and how much to
> offset the  tracking code.

Yes, that's one problem.  But there are two types of GPS receivers.  The 
common ones are optimized for navigation: location and velocity.

The other type has slightly different firmware optimized for timing.  If you 
know where you are located, you can do a better job of interpreting the noisy 
data and/or get decent time with as few as 1 satellite.

I suspect your unit is confused because it "knows" the wrong location.

The manual for the Z3801A is widely available on the net.  (If you can't find 
it, I'll mail you a copy.)  It has good descriptions of the status page and 
the survey process.

If you have a terminal program you can probably figure out how to talk to to 
your 3805.  The Z3801A runs at 19.2, 7 bits, odd parity.  I don't know about 
the 3805 and a quick google didn't find anything.  If you can't find it with 
trial and error, somebody on this list knows.

If you send it ":SYSTEM:STATUS?" a Z3801A will send you back a status page.  
In particular, there is a chunk of the page that shows the satellites it's 
using and the ones it's trying to lock up to.

":GPS:POS:SURV ONCE" will tell it to do a survey.  (That's assuming it's the 
same as a Z3801.)  It will take a long time, depending on how good your 
antenna is.  You can watch the progress with the status page.

The commands above may need the right CR/LF type magic after the text string. 
 My notes don't say anything so I expect the 3801 is forgiving.  (Or I was 
lucky.  I'm running Linux so my luck may not transfer to Windows.)

In this context, the Z3801A is different from the TBolt.

The Z3801A automatically saves the new location in Flash when the survey 
completes.  The TBolt doesn't do that unless you tell it to.

So on power up, the Z3801A that was working but has been moved to a new 
location will be confused because it has remembered the wrong location.  On 
the other hand, a TBolt that was never told to save its location will 
automatically do another survey and eventually start working.

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

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