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 SBAS and GPS Accuracy - Side by Side Testing

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gpspassion Posted - 22 avr. 2006 : 02:58:25
May/June/July 2006 SBAS Poll Results:
Useful and use it : 48% - Useful but don't use it : 18% - Not useful don't use it : 34%

SBAS (WAAS/EGNOS) - Side by Side Testing

This article started out as an attempt to come up with some real life data to answer the recurring questions about SBAS (Satellite Based Augmentation System - known in various parts of the world as WAAS, EGNOS, MSAS) with everyone being logically convinced they need it after reading the technical specs of GPS systems where SBAS accuracy is generally shown as being much better than non-SBAS accuracy, typically 10 meters down to 5 meters or even 2 meters...For some fair testing, I had to find a way to measure a reference point with the best possible accuracy and that's where the Delorme GPSPostPro suite comes in, so I added a page in this article describing how I used it.


Questions, comments ?
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pyxis Posted - 25 déc. 2007 : 17:59:11
An additional comment pertaining to the Elevation Mask is that DGPS corrections were constrained to apply only to Satellite Elevations above 10.0 degrees. The default Elevation Mask value for the SIRF II chipset was 7.5 degrees. The default value for the SIRF III chipset is 5.0 degrees.
pyxis Posted - 25 déc. 2007 : 17:52:59
I would not be concerned with the grayed out Tracking Parameter.From all indications the TRACKING parameter under Power Mask is not implemented. However, the NAV parameter is implemented and adjustable. It can be set somewhere around 12 to 15 dBs for the SIRF III since the principal characteristic of this generation chipset is its ability to correlate inputs with much lower signal to noise ratio than previous chipsets. The SIRF II operating value was around 24 to 28 dBs. In SIRF Protocol mode watch the C/No value. You will notice that many of the satellites being used in the Fix are lower than 28 dB. Experiment with the Power Mask NAV and the Elevation Mask to find your optimum operating setup.
musky Posted - 25 déc. 2007 : 15:03:59
If SirfDemo won't modify the mask, I don't know any alternative way to do it. Maybe another piece of "tweaker" software out there?

It could be SirfDemo does not implement that function correctly, or maybe the GPS is blocking the power mask command.

You might want to check out this thread on this forum:

This is back when we were trying to solve the SirfIII WAAS issues. aaronprez was trying to mess with the power mask.....
zjdcjyj Posted - 25 déc. 2007 : 04:36:51
I found satellites signal often near 20db,but power mask for tracking is 28db default,So GPS FFTT is very long.
I want to modify power mask for tracking to 20db.
Can you tell me how to do it?
musky Posted - 24 déc. 2007 : 14:10:53
Respectfully asking, why do you want to modify the power mask for "tracking" ??
zjdcjyj Posted - 24 déc. 2007 : 04:07:58
My GPS is Nokia LD-3W(Sirf StarIII inside)
when I use Sirfdemo,I found I couldn't modify power mask for tracking
musky Posted - 23 déc. 2007 : 14:38:11
Are you referring to Sirf or MTK?? If it's Sirf, SirfDemo may be able to do that. If it's MTK, then probably no. MTK does not have a binary mode with all kinds of parameter tweaking available like Sirf does. They do have some NMEA extensions available. See the Transystem document for these extensions. I just looked through the document and did not see any power mask commands.
zjdcjyj Posted - 22 déc. 2007 : 17:04:00
Now,Can anyone tell me how to modify power mask for tracking?Thank you!!!
Zigster Posted - 11 mars 2007 : 00:08:38
yes I'm in for testing!

thanks for the new thread, I'll post there from now !
gpspassion Posted - 11 mars 2007 : 00:02:53
CE version would be great yes and you can use this method and I started this * Discussing MTK receivers and Tips and Tweaks * thread where you can post it as well as your previous MTK comments.
musky Posted - 10 mars 2007 : 23:36:22
Ok, I've got the MTKTweak app ready here. I've got a Windows version, I can also do a CE version if anyone's interested. All it does now is turn WAAS on and off.
GPSPassion, is there a place on your server I can upload this app?
Zigster, you want to test it?
gpspassion Posted - 10 mars 2007 : 23:03:02
I see, a 737 clone, best for you to post in the 737 thread then.
Zigster Posted - 10 mars 2007 : 22:52:44
sure can:

bought it @ebay from a shop in London.
It calls itself iBT-GPS, and has the same packaging as seen on .

I just mailed polaris on information on three points:
1. WAAS/EGNOS support enabled ?
2. USB bridge available (for now I can use the miniUSB for charging only?
3. 5Hz update enabled or or can it be turned on?

I wonder, if I will receive an answer. I will keep you updated.


gpspassion Posted - 10 mars 2007 : 21:44:34
Musky, again interesting MTK research but largely OT here, and people missing on it, you should start a new MTK thread with some cutting and pasting of your previous messages.

@Zigster - only Polaris I've seen was a Sony chip, got a link for the MTK version ?
Zigster Posted - 10 mars 2007 : 20:04:26
thank you for your information.
My unit is Polaris iBT-GPS. It has a USB port, but, as it seems, it is only meant for charging the battery (no device is being recognized, when plugged into the USB port of my computer. I actually tried to communicate via Bluetooth to the device with HyperTerminal already, but to no prevail.
I'm also a software developer...perhaps I can chip in with some help on clearing the fog on the MTKs. I'm looking forward to hearing from you and if you don't mind, I would like to check out your tool ... :-)



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