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ContinuousWave: The Whaler GAM or General Area
|Author||Topic: GPS Error|
posted 04-05-2001 11:36 AM ET (US)
Installed the new Lowrance X15mt with gps package. Estimated position error is at best 40 feet, sometimes as high as 70 to 80 feet.When I compare my hand-held Garmin unit it tracks the same satellites but with estimated position error as low as 12 feet at the same time the Lowrance shows epe of 45ft. Lowrance tells me the unit is within
acceptable range so there is nothing I can do.
I don't know anything about this but I know the members of this board will tell me if I should be concerned. I can't believe a $100 hand-held is more accurate.
Thanks for your suggestions
posted 04-05-2001 02:11 PM ET (US)
One question to ask is does Lowrance and Garmin calculate EPE in the same way? Is the determination of EPE done through with a standard algorithm used by all manufacturers? Is it safe to assume that the Lowrance has a 12 channel receiver? FYI, my 8 channel Garmin handheld now that SA is turned off will obtain about 40 EPE at best. My 12 channel Garmin handheld will usually achieve 11 EPE at best under the same conditions.
posted 04-05-2001 05:17 PM ET (US)
The different manufacturers use different
algorithm's to come up with their accuracy
number, which is generally wildly
pessimistic. And they absolutely positively
won't discuss how they calculate it.
DOP (dilution of precision) is, I belive a
Consumer GPS units of the same type all have
Nonconsumer units (survey grade stuff) can
The units do vary in their abilities under
posted 04-05-2001 07:20 PM ET (US)
Chuck - My older (1995) Lowrance GPS is a five channel. Would this be a lot less accurate than a 12 channel? I do have a Differential receiver added to it.
Incidentally, I have recently entered waypoint Lat/Lons, saved ON LOCATION from a previous Lowrance LORAN, into my 12 channel Lowrance DGPS, and found the old Loran waypoints to be off by as much as 1/2 mile! I am amazed at the difference. I had thought Loran was pretty accurate on an absolute Lat/Lon basis.
posted 04-06-2001 09:06 AM ET (US)
Your old unit should be close to as accurate
as the current 12-channel units, but not
quite. 5 birds is sufficient for a fix.
If there are more, as 12-channel receiver
will have some redundancy. With DGPS,
your 5-channel unit should be fine.
LORAN isn't terribly accurate as far as the
posted 04-06-2001 09:56 AM ET (US)
As Chuck pointed the only thing 4 or more channels gives you is redundancy they do not make the GPS more accurate, they do provide back up and error correction if it looses contact with any of initial satellite fixes --- adding DGPS to any GPS and I'm sure the new "fuzzy WAASIE" will provide excellent positioning.
We experienced great accuracy on the trip up the ICW last Spring with no DGPS (had 1200 plus miles to play with it)! When we installed DGPS (which by the way can only use one one station at a time even if there is an overlap of coverage) later on it was amazing the pin point accuracy --did some testing last summer. If I can locate my notes will post them.
We have a shorter trip in store this Spring only about 600 miles and we'll have Loran, GPS with DGPS --- should be interesting --- (chuckle --- if the Atlantic cooperates we will have a shorter and faster trip -- outside than inside after Hatteras)
posted 04-06-2001 11:13 AM ET (US)
I had saved a site from a earlier posting that has GPS data www.joe.mehaffey.com and has a forum. I would be interested in knowing what handheld / fixed GPS everyone would choose if money is not a factor. New Leica any good? I currently do not own one but will probably buy a handheld this season. Thanks
posted 04-06-2001 04:56 PM ET (US)
Handheld: Garmin eTrex Vista. I have one on
backorder. WAAS. 24M flash builtin for
charts (that's a MESS of charts -- My 162
is more than accurate with 3M). Barometric
altimeter (yawn, I know how high the surface
of the ocean is), fluxgate compass.
The eTrex Legend is a good choice too (8M,
There's also a new GPSMAP 76 worth looking
posted 04-07-2001 05:37 PM ET (US)
Other than the gps accuracy, how do you like the new Lowrance? I am about to buy one. Here is what I am thinking, though. Like you, I have a handheld Garmin (a III+). The gps interface on the X-15 is NMEA. The gps kit for the X-15 is basically just an antenna. There should be a way to attach the Garmin to the X-15, using a self made cable, and have it furnish the signal to the X-15. It looks like I would have to buy an NMEA cable for each piece, cut the ends off, and attach them together to get them to fit the respective units. Does this make sense to anyone? I don't want to have to buy the Lowrance gps attachment until it is WAAS capable.
Just a thought.
posted 04-07-2001 06:56 PM ET (US)
That ought to work. Maybe. The GPS upgrade
for the Lowrances includes the GPS,
cartography on CD, an 8MB memory card, and
the PC interface cable. I'm not 100% certain
you'll actually be able to use it as a GPS.
I'm not a big fan of combo GPS/fishfinders.
For the Garmin, get the power/data cable.
posted 04-07-2001 07:40 PM ET (US)
Just went to www.joe.mehaffey.com and they review the Garmin Vista / Legend and there is a link to worlds largest GPS store. The review is way over my head but I think I will buy the Vista. Thanks
posted 04-08-2001 06:56 AM ET (US)
After fooling with the X-15 for a week, I don't know how to answer your question. After I paid the extra $ for the dual (50/200) 'ducer, a friend on the Lowrance Pro Staff called and said DO NOT use the dual
but switch to the straight 200 'ducer which I did. The dual 'ducer does not do well in shallow water applications.
I am not very skilled in this and I have
had a heck of a time getting the gps to send data to my Icom (dsc) radio. Lowrance was of no help on this, in fact, customer service gave me incorrect info. Today, the gps "hunts" to acquire position- 1 second locked on- the next second lost.
I replaced a Furuno dgps and Zercom fish-finder with the X15 and I already miss the simplicity and accuracy of the Furuno. I
think after I survive the learning curve I will be pleased but I'd download the manual
and go for a ride on a boat that is using the unit befor you decide. There is a lot to be said for separate units. I'd rather be fishing.
posted 04-08-2001 10:49 AM ET (US)
Well, I have neither of these units, but
I did get my Garmin 162 to talk to my
Standard Horizon Spectrum. Lowrance's
manual is online, but Icom's isn't, so I
can only conjecture about that side.
Wire X-15 COM2 transmit (blue) to the
I just noticed that the X-15 generates NMEA
Are you indoors when the GPS is having
I love the line in the X-15 manual: "Never
posted 04-08-2001 11:30 AM ET (US)
Thank you for the help. Chuck, the wiring was correct- all it took was to configure port 2 to send nema output and to set the baud at 4800. I also moved the boat and the unit locked on. Thank you for doing what customer service could not.
posted 04-08-2001 12:30 PM ET (US)
BTW, this stuff is way harder than it should
be. I have a masters degree in electrical
engineering, and it took me about a day of
fooling with it to get to work. Every unit
seems to be just a little bit different, esp.
Please pass your results back to customer
posted 04-08-2001 11:32 PM ET (US)
I downloaded the most recent info into my
168 garmn. Today I was cleaning the boat
and marked the driveway as home on the gps.
About an hour later I turned the garmin back
on and searched for the nearest waypoints.
The distance constantly changed from 1.5ft
What is the proper way to check for
posted 04-09-2001 12:03 AM ET (US)
First: have you loaded the latest firmware
into your 168? That will add WAAS and
improve the accuracy. Or is that what you
meant by "latest info"? And after you load
the new firmware, you have to enable WAAS
(hit menu on the panel with the signal
strength bars), then let it take about an
hour to figure out where the new bird is.
Once it locks in WAAS, you will see the
letter D on the signal strength bars.
What you did is one way of knowing what the
And if you have a way to hook
Earlier in this thread, I said I thought DOP
posted 04-09-2001 10:47 PM ET (US)
I'm now chasing fish around the gulf with the
posted 04-10-2001 09:17 PM ET (US)
And the fish are probably still laughing
just as hard.
One of the funniest things I've ever seen
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