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Date: Thu, 17 May 2007 21:20:25 -0400
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From: Tim Olson <Tim@5000feet.com>
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Subject: Re: [LML] Periodic Chelton GPS Failure...Any Ideas?
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Jeff,
First, if you have a Chelton, and you have a Crossbow AHRS, you will
want to make sure you have the latest updates to the AHRS built-in
GPS.  There were issues last season that were uncovered and fixed,
and recently some new issues have come to light, all related to the
GPS that's built in.  In addition, the antenna that many people 
received, a small "postage stamp" antenna, is not a great one to go
with for the install, and Xbow is not recommending that antenna at
all be used.  They have preferable Antcom antennas that they have
found to greatly improve reception.  Once you have all of that
taken care of, you would probably be in good shape regarding GPS.

Tim

Jeffrey Liegner, MD wrote:
> Here's another Chelton item.
> 
> I'll be flying along and will get a "GPS Failure" announcement with loss 
> of terrain info, plus DR (dead reakoning) counter.  After 1 or 2 minues, 
> the HITS boxes leave (as expected).  Then in three to five minutes the 
> GPS signal is restored, and all is well.  In my recent 3.5 hour flight 
> to/from St Louis, it dropped out three times each way.
> 
> So I have looked at the antenna mounted under the top of the dash, just 
> behind the panel, and it is secure and powered correctly.  I have 
> checked the wiring to the Chelton and all is secure and fine.
> 
> The "GPS Failure" can occur whether the dashboard is installed or the 
> GPS antenna is uncovered, meaning the particle board vinyl is not the 
> obstruction.
> 
> I wonder if the location, behind the top part of the panel, with what 
> seems like an excellent view of the sky, gets blanked out by the roof 
> edge of the large front windscreen, reducing the satellites by a 
> couple.  Is there a way to check the satellites seen by the antenna?
> 
> The GX-60 antenna located near by, equally behind the panel looking up 
> through the same windscreen, does not drop out like this.
> 
> It's been doing this off/on since the beginning.  At first I thought I 
> didn't think too much about it, and then I started to rely on it more 
> and more, and now I learn from others that this is not a problem with 
> other installations.
> 
> Your ideas?
> 
> Jeff Liegner
> LIVP (N334P)
> 
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