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Date: Fri, 2 Apr 2010 17:13:52 +0100
Message-ID: <h2rfc7eccec1004020913re3be60eev875f4880226b9edb@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@googlemail.com>
To: ukmicrowaves@yahoogroups.com, rsgb_lf_group@blacksheep.org, 
	uk_beacons@yahoogroups.com
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Subject: LF: Motorola GPS Time Oddity
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I've noticed a curious odditity on a Motorola M12 GPS module, when started
up completely from cold with no stored almanac data:  When the
module eventually 'appears'  to lock up and show the correct lat /long and
the NMEA data showing satellite staus 'Valid', the NMEA reported time is 15
(ish) seconds out.   Which means it hasn't downloaded the leap-second
correction yet and is still working on GPS time - the NMEA report gets
corrected after a minute or two longer wait.

BUT... Why does it decide that it has enough info for location calculation
when it clearly hasn't yet downloaded all the almanac data ?
It's lying.    Has anyone met this?
Only the M12 behaves like this out of those tested.  All other modules I've
used, including the older Motorola. Oncore,. give the correct time
immediately they show lock.   Of course, if the internal battery is alive
the almanac data is already stored and it jumps into life immediately with a
warm start, but after several months of storage - sometimes just weeks -
this battery goes flat.

Andy
www.g4jnt.com

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<div>I&#39;ve noticed a curious=A0odditity on a Motorola M12 GPS module,=
=A0when started up completely from cold with no stored almanac data:=A0 Wh=
en=A0the module=A0eventually &#39;appears&#39;=A0 to lock up and show the=
 correct lat /long=A0and the NMEA data showing satellite staus &#39;Valid&=
#39;, the=A0NMEA reported time=A0is 15 (ish)=A0seconds out.=A0=A0 Which me=
ans it hasn&#39;t downloaded the leap-second correction yet and is still=
=A0working on=A0GPS time - the=A0NMEA report gets corrected after a minute=
 or two longer wait. </div>

<div>=A0</div>
<div>BUT... Why does it decide that it has enough info for location calcul=
ation when it clearly hasn&#39;t yet=A0downloaded all the almanac data ?</=
div>
<div>It&#39;s lying.=A0=A0=A0 Has anyone met this?<br></div>
<div>Only the=A0M12=A0behaves like this out of=A0those=A0tested.=A0 All ot=
her=A0modules I&#39;ve used, including the older Motorola. Oncore,. give=
 the correct time immediately they show lock.=A0=A0 Of course, if the inte=
rnal battery is alive the almanac data is already stored and it jumps into=
 life immediately with a warm start, but after several months of storage=
 - sometimes just weeks -=A0 this battery goes flat.=A0</div>

<div><br clear=3D"all">Andy<br><a href=3D"http://www.g4jnt.com">www.g4jnt.=
com</a><br></div>

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