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Pedro-G
27 Posts |
 Posted - 09 sept. 2005 : 08:24:34
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In short, when speed exceeds about 300km/h, the unit goes in to a short of "semi-fix" mode, where the green light on the unit is flashing to indicate a fix, but in all the PDA software the status is "No Fix". Altitude is displayed correctly.
Has anyone else seen this problem on the RBT-2001 or any other receiver?
For more info, here is the message I send to Royaltek support. I haven't got an answer yet:
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I have recently purchased the RBT-2001 for using with my iPAQ hx4700. It seems to be a very sensitive receiver, the signal levels are very good. The unit works very well in car and hiking.
According to specifications, it should work when altitude is less than 18,000 meters, velocity is less than 515 meters/second (about 1850km/h) and acceleration is less than 4G.
However, it NEVER keeps the fix when speed exceeds about 300km/h. I have tried it on three flights:
The first one was a piston engine aircraft. The speed was 200-250 km/h, and the receiver worked very well. The signal levels were good according to Royaltek GPS Demo and other utilities (WinFast Navigator, VisualGPSdemo). The moving map software I use, MemoryMap Pocket Navigator, worked very well.
The second flight was on a turbo-prop. The signal levels were very good, the unit was tracking nine or ten satellites. During taxi and first minutes of the flight the receiver worked well. However, when the speed exceeded about 300 km/h, the receiver suddenly lost the fix solution. In Royaltek GPS Demo (and other software) it showed that the unit was still tracking 8-10 satellites with strong signal levels (mostly 30-36), but all the bars turned blue (they are green when there is a fix). Under "Mode" it said "No Fix". Altitude for the flight was 2000-3000 meters.
The curious thing is, that the green light on the unit KEPT FLASHING all the time to indicate a good fix, the unit was able to tell the correct altitude all the time, and even the longitude and latitude updated logically some of the time. But the status was "No Fix" in all the software I checked. MemoryMap Navigator occationally showed the correct position on the map (since it sometimes updated), but the position indicator turned grey, which means no fix, and the software was practically unusable.
After some time I forced a cold start with the Royaltek GPS Demo. After less than a minute the cold start was completed, the bars turned green and the Fix Mode was "3D". This lasted about one or two seconds, after which the unit reverted to "No Fix".
For the rest of the flight (about 350km/h), there was no fix. When we slowed down for approach, the fix was established, when the speed slowed down to about 200-250km/h.
The third flight was on a jet. The signal levels, once again, were very good inside the cockpit, and the unit worked well during taxi. However, the start was rather aggressive (full throttle against brakes, then release brakes), and the receiver lost the fix during acceleration, while the jet was still on ground. The speed that time was around 200km/h. The acceleration, however, was surely much less than 4G:s.
The speed during the flight was around 800-900km/h, and the receiver was unable to get a fix during the whole flight, even though signal levels were good and the green light on the receiver was flashing. Altitude was declared correctly. The fix was established shortly after touchdown, when speed was about 200km/h.
So, how do you explain the specification: Velocity less than 515 m/s? Have you actually TRIED to use the unit at aircraft speeds, or is this just a theoretical specification? The unit is not suitable for what I got it for. Or is my unit faulty?
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gpspassion
93392 Posts |
Posted - 09 sept. 2005 : 14:05:03
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Ok, well let's stay constructive here ;-) All civilian GPS systems are limited to speeds of 515m/s under the US export law I believe and you need special authorization to have that lifter.
A few things might be happening, the first that comes to mind of course is the jetlag bug, but that was fixed with 3.1.1 and all the RBT2001's had that version. I have not used the RBT2001 in a plane yet, but other SiRFstarIII receiers 3.0.2 or 3.1.0 worked fine at 900+ kph (other thant the occasional jet lag problem fixed by a cold reset). It does look like they are somehow "shutting" off the fix although it might be something else, but the blinking light might be a clue that there is a problem. If you can record a raw NMEA log with say VisualGPS CE to see if other problems can be identified.
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Pedro-G
27 Posts |
Posted - 10 sept. 2005 : 09:43:43
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Ok, I'll try to get a raw NMEA log in a week or two.
I don't quite understand which part of my post you felt was "unconstructive". Do you refer to the last part where I demanded an explanation from Royaltek for the specification: Velocity less than 515 m/s?
I didn't mean that I need the unit working faster than 515m/s, I can live with that limit. But clearly the receiver doesn't live up to the specs, nowhere near. Since it stops working correctly above (about) 300 km/h the correct spec would be: Velocity less than 85 m/s (or so), which is much poorer than 515 m/s. Quite like you'd by a car with a stated top speed of 260 km/h, and it would actually only do 50 km/h.
It's possible that Royaltek hasn't actually tested the unit at high speeds, they are maybe using specs from SiRF or something, and there is something wrong with the implemenatation of the receiver. |
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gpspassion
93392 Posts |
Posted - 10 sept. 2005 : 16:17:07
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Well yes, and the shouting implied by using capital letters, it's not called for and will likely only annoy people reading it. As explained in my reply, it's not just a "specs" issue as there is only that 515m/s limitation on receivers imposed by the government, so this would be out of Royaltek's control as it is likely due to the firmware programmed by SiRF as was the jetlag bug that I referenced in my reply. No one has pointed out this problem so far, let's see if these forums can help get the ball moving like they did for the jetlag bug.
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Pedro-G
27 Posts |
Posted - 10 sept. 2005 : 20:16:03
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Gotcha. I'll try again and log the NMEA.
I'll also get my hands on the TomTom MkII that I had for short while, but gave up for the Royaltek. I haven't tried the TomTom MkII over 300km/h, but I vaguely remember reading that someone tried it on a commercial jet flight and it was OK.
Testing the TomTom will make sure that the problem is not something I'm doing wrong, but actually is a flaw in the Royaltek unit or SiRF 3.1.1 (provided that the TomTom works with me at high speeds).
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gpspassion
93392 Posts |
Posted - 10 sept. 2005 : 21:18:16
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It should yes, I had a bunch of SS3 when I flew in June and July and they all worked, they were running the FW3.0.2. In facto, other than the problem you've described I've never seen that type of speed problem reported, regardless of the GPS or chipset.
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Lizard_weasel
USA
885 Posts |
Posted - 10 sept. 2005 : 21:43:51
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I was on a jet yesterday with a tailwind. Ground speed was tracking at 620mph which is right at 1000 km/h.
Dell Axim x50v/Globalsat BT-338 Bluetooth GPS/1gb Lexar SD card/2gb Kingston CF card. Mapopolis 4.6pre6 with North America NE maps. |
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gpspassion
93392 Posts |
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Lizard_weasel
USA
885 Posts |
Posted - 10 sept. 2005 : 23:52:39
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Yes, it has 3.1.1.
Dell Axim x50v/Globalsat BT-338 Bluetooth GPS/1gb Lexar SD card/2gb Kingston CF card. Mapopolis 4.6pre6 with North America NE maps. |
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gpspassion
93392 Posts |
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Pedro-G
27 Posts |
Posted - 13 sept. 2005 : 11:03:04
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Edit: removed some questions to which I figured out answers myself.
Ok, I took the RBT-2001 with me on a flight and logged the NMEA in different situations, such as acceleration over 300km/h, deceleration under 300km/h, forcing a cold start etc. The logs and detailed explanations of the test flight can be found at:
http://koti.mbnet.fi/pedro-g/RBT-2001/RBT-2001.htm
I did some interpretation of the NMEA, quite clearly there is some flaw in the receiver. I'd like more people to look at the logs say their opinions.
I didn't think of trying SIRF protocol, I'll try that next time. |
Edited by - Pedro-G on 14 sept. 2005 11:27:29 |
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gpspassion
93392 Posts |
Posted - 14 sept. 2005 : 11:44:32
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Brilliant testing ! Thers is indeed something going on at 300kph (or 162nmph as this is what is reported in the VTG data). See what happens with SiRF although I'm not sure how you would analyze the results, but you can see what happens live.
Since I think Royaltek were the first to use the 3.1.1 firmware, I wonder if it didn't get fine-tuned after that for the Globalsat 338 version for instance.
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Pedro-G
27 Posts |
Posted - 14 sept. 2005 : 12:21:31
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Right, I can't log the SiRF data, VisualGPSce doesn't connect with SIRF protocol. Is there a PPC software for that?
And it's in binary anyway, kind of hard to analyze...? |
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gpspassion
93392 Posts |
Posted - 14 sept. 2005 : 12:23:27
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Yes, but you can see if you're still getting speed readings, I think OziCE can read SiRF now or CE Monitor will of course.
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patriot
7 Posts |
Posted - 15 sept. 2005 : 07:39:17
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Hi,
I bought the RBT-2001 on the spec that it would work up to 515m/s. I am using the O2 IIs as a PDA on com 6. Initially I had the same problem of the speed and heading information dropping out at around 300kph - curiously it was still accepting lat and long information. I found after some fairly extensive research (don't bother with the RoyalTek website) and playing around the limitation appears not to be in the GPS rather in the programs used and how they interpret the NMEA/ SiRF data. The way I got around it unfortunately is only a partial fix. I use the SiRF Demo program (but I believe CE Monitor or GPSTweak will do the same thing) on my laptop (Toshiba Satellite M40) to select NMEA for operating below 300 kph and SiRF for operating above. The additional problem is that many programs don't appear to be fully compatible with SiRF - they appear to be built for walking or driving in cars not flying at just under 1000 kmh. I got GPS Tuner to work on NMEA below 300kph and OziExplorer to work above and below 300kph on SiRF. None of the other setting such SBAS, DGPS and DOP setting seemed to make any difference since they appear to only be available for SiRF. For NMEA I used GGA - 1sec, GSA - 5sec, GSV - 5sec, RMC - 1sec and VTG - 1sec.
If anyone knows of a list of programs that works with SiRF it would be greatly appreciated. |
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Pedro-G
27 Posts |
Posted - 15 sept. 2005 : 17:14:11
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RBT-2001 works indeed fine with SiRF protocol over 300kph! I tested it today, albeit only up 374kph, it'll take a couple of weeks before I get a chance to test it at higher speeds.
Using SBAS with NMEA does work under 300kph, I get the "Differential GPS" status in VisualGPSce. However, turning SBAS on didn't help with the NMEA 300kph barrier.
For navigating, I use the Memory-Map Pocket Navigator, which works with SiRF. I works perfectly, expect it doesn't show the satellite info, but it's no biggy. I'm basically all set now! (Provided that RBT-2001 works with SiRF at higher speeds as well.) I'm not planning on sending back the receiver, it's usable.
With SiRF protocol, satellite info can naturally be seen with CE Monitor ( = WinFast Navigator). It's a shame, though, that it doesn't show whether or not Differential GPS mode is on. VisualGPSce would show it, but it doesn't work with SiRF protocol. CE Monitor does show the EGNOS satellite signal strength, but you don't know if SBAS is actually utilized in the fix. BTW, EGNOS satellites get different names in CE Monitor in SiRF mode compared to NMEA more. For example satellite 33 appears as 1203F or 1202D (yes, five characters) in SiRF.
I got an answer (or actually two) from Royaltek:
"We are pass your question to SiRF company, but have not answer now, We will feedback to you when we received the answer form SiRF."
and:
"Sorry about our delay. We just got informed the current version of SiRF StarIII limited the velocity since the drift issue. Any it should be solved by next version. As for the schedule of new version, sorry, we are also waiting for the response by SiRF."
I also tried to contact Carl@Sirf by email, directing him to this thread, but so far he hasn't commented on this. I don't know if I had the right email address, anyway. |
Edited by - Pedro-G on 15 sept. 2005 18:06:01 |
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Royaltek RBT-2001 won't work over 300km/h ?
