RAIM errors and the Apollo GPS

We've been getting RAIM errors in Southern and Central California with
our GX60 in the past couple of months. The unit recovers in a minute
or so and there doesn't seem to be a pattern (e.g. in a turn, special
altitudes) to the failures. Yes, I know about the earlier discussions
of RAIM error and the GX** but it seems like the frequency is
increasing dramatically. I also note that there are more NOTAMS for
GPS "outages" that sometimes reach our area, 'tho they don't seem to
correlate well with the errors I get. I assume its the military trying
to learn how to jam GPS.

My specific questions:

1) Does anybody else see more RAIM errors than, e.g. a year ago? What
manufacturer/times/places?

2) Do the military interruptions (or whatever is the source of the
NOTAMS) usually last a few minutes?


Lee Elson

(Lee Elson) wrote in
om:

We've been getting RAIM errors in Southern and Central
California with our GX60 in the past couple of months.

RAIM warnings (not errors) occur when the unit predicts
satellite reception that doesn't give acceptable precision in
calculating position. It's usually satellite geometry problems.
The GPS satellites aren't stationary, but move around the earth
in approximately (but not exactly) 12 hour orbits. Sometimes
all the satellites are directly overhead, or on the horizon, or
not enough are visible. When all satellites in view are
directly overhead, or nearly so, the position error is greater.

--
Regards,

Stan

Lee,
What version of system software do you have?
Version 3.5 is the latest, and was issued to correct an overly cautious
RAIM prediction model in the earlier versions.

Since getting mine updated (a year or more ago) I rarely get a RAIM warning.

Rich


Lee Elson wrote:
We've been getting RAIM errors in Southern and Central California with
our GX60 in the past couple of months. The unit recovers in a minute
or so and there doesn't seem to be a pattern (e.g. in a turn, special
altitudes) to the failures. Yes, I know about the earlier discussions
of RAIM error and the GX** but it seems like the frequency is
increasing dramatically. I also note that there are more NOTAMS for
GPS "outages" that sometimes reach our area, 'tho they don't seem to
correlate well with the errors I get. I assume its the military trying
to learn how to jam GPS.

My specific questions:

1) Does anybody else see more RAIM errors than, e.g. a year ago? What
manufacturer/times/places?

2) Do the military interruptions (or whatever is the source of the
NOTAMS) usually last a few minutes?


Lee Elson

Rich wrote in
:

What version of system software do you have?
Version 3.5 is the latest, and was issued to correct an overly
cautious RAIM prediction model in the earlier versions.

Since getting mine updated (a year or more ago) I rarely get a RAIM
warning.

We've been getting RAIM errors in Southern and Central California
with our GX60 in the past couple of months. The unit recovers in a
minute or so and there doesn't seem to be a pattern (e.g. in a turn,
special altitudes) to the failures. Yes, I know about the earlier
discussions of RAIM error and the GX** but it seems like the
frequency is increasing dramatically.

I too have noticed a lot of them lately on my GX60. Some of this has
been out in New Mexico and I have tended to discount them for that
reason, even though they were outside of any NOTAM'd hours for trouble.

I am not running the latest software, partly because UPSAT never told me
that it existed, and partly because I am annoyed with them anyway (long
story).
jmk

Rich wrote:
Lee,
What version of system software do you have?
Version 3.5 is the latest, and was issued to correct an overly cautious
RAIM prediction model in the earlier versions.

....and versions 3.0 - 3.4 are the subject of an AD.


Since getting mine updated (a year or more ago) I rarely get a RAIM
warning.

Rich


Lee Elson wrote:

We've been getting RAIM errors in Southern and Central California with
our GX60 in the past couple of months. The unit recovers in a minute
or so and there doesn't seem to be a pattern (e.g. in a turn, special
altitudes) to the failures. Yes, I know about the earlier discussions
of RAIM error and the GX** but it seems like the frequency is
increasing dramatically. I also note that there are more NOTAMS for
GPS "outages" that sometimes reach our area, 'tho they don't seem to
correlate well with the errors I get. I assume its the military trying
to learn how to jam GPS.

My specific questions:

1) Does anybody else see more RAIM errors than, e.g. a year ago? What
manufacturer/times/places?

2) Do the military interruptions (or whatever is the source of the
NOTAMS) usually last a few minutes?


Lee Elson





--
Dave Butler, software engineer 919-392-4367