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Globalsat BT-359 - SiRFIII v2
Posté le 30 juin 2006 à 00:09:13 par gpspassion.

Globalsat BT-359 - SiRFstarIII v2



The full user experience, from delivery to field testing and...cracking it open


Green : iBlue Nemerix v4 (unreleased) - Blue : BT-359 - Red : BT-338
The Class of '06 deals better with multipath (bounced signals) in this challenging environment under trees and next to tall buildings in a counter-alley. The BT-338 jumps to the other side of the street as other SiRFstarIII v1 receivers tended to do in this type of environment.

The BT359's reduced form factor does not come at the expense of performance, even with a patch antenna about half as thick as on the BT338. The signal levels of the Nemerix v4 iBlue are not directly comparable as it is based on a different chipset and numbers may be reported differently.



Taking after the BT-338
The Globalsat BT-359 has been much anticipated since it was first seen (bottom left of picture #6) at the CES show in January 2006 although at the time Globalsat had chosen another form factor for the receiver that would follow in the very successful footsteps of the BT-338, "the" SiRFstarIII Bluetooth GPS receiver with serial numbers now in the 70,000 range likely indicative of the number of the units produced. Apparently Globalsat changed their plans because they felt the form factor would be a good way to preserve performance, certainly a good reason and we'll see that they met their goal.

An Improved Design
Globalsat have come up with a very slick design with two slightly different casings, the "S" and "W" versions. While the BT338 certainly looked alright, it remained a bit "techie", the BT359 is more refined, brighter finish and much thinner as can be seen below. Even the TomTom MkII receiver that impressed when it came out feels a bit "rough" next to the BT-359 and the latter uses a more efficient patch antenna versus the helix antenna in the former. I'm generally more interested in the performance and features, but if it looks good, I'll take that too and slip it in my shirt pocket !

Like the BT-338, the BT-359 has only one connector, for DC power, but this time the classic 4mm "iPaq type" jack has been replaced by a miniUSB plug. This will actually come in handy as there are many extendable miniUSB cables but few with an iPaq type jack. Unlike the Holux or Wintec receivers USB is for power only, data connections will be via Bluetooth. Nothing specific here, it works as planned with the standard "0000" pairing code.

One connector means that there is no connector for an external GPS antenna so those equipped with a coated windshield will need to place it under the rear window to maintain accurate guidance in difficult urban environments.

Advanced Power Management
The BT-338 introduced a very convenient "auto-off" mode with the receiver powering off when the Bluetooth connection was not used for 10 minutes, a good way to extend battery life for those of us who would forget to switch off our GPS receivers. This is back on the BT-359 of course, with a twist since the "auto-off" is deactivated when the receiver is powered via USB. This addresses one frequent request from users who wanted to leave their receiver powered on at all times in a hidden spot in their car. However the BT-359 will turn itself off if power is lost and will not turn itself off on again if power resumes, so those who need this will have to wire their car accordingly. Based on recent feedback in the forums, it would seem that this feature has been implemented on the more recent BT-338 models as well UPDATED 07/08 : this has now been confirmed

Preserved Battery Life
As can be seen above, the Lithium-Ion battery that powers the BT-359 has been slimmed down quite a bit compared to the one used in the BT-338, and the rating has dropped by 25% from 1700mAh to 1300mAh, but the good news is that the battery life only loses 15% from 17.5 to 15 hours. This was likely achieved thanks to the slightly lower power consumption of the new "single chip" SiRFstarIII chipset compared with the "dual chip" (RF+Baseband) used on the original SiRFstarIII receivers.

The time to power ratio is now at 0.68 instead of 0.60 but we're still very far from the 1.7 of the NemeriX based iBlue that also performs very well now with the v4 firmware (see Field Testing - Part I above). Let's hope that the recently announced SiRFstarIII LP chipset announced at 3GSM will bring more improvements in this area.

Solid GPS Performance
We've seen recently with the TomTom GO AIOs that a new generation didn't necessarily mean improved or even similar performance or that the presence of SiRFstarIII was not a guarantee, see the iMate PDA-N/Pharos 525 or Mio P550 and the streamlined form factor of the BT-359 was some cause for concern.

My BT-359 test unit uses the 3.1.1 firmware as the BT-338 and not the more recent 3.2 firmware seen on other receivers although it remains unclear at this time what may have changed.

Time to first fix (TTFF) is what we have come to expect from current receivers without external assistance, about 45 seconds for a cold/warm start in good conditions and thanks to the correlation power of SiRFstarIII it remains consistent as long as there is enough signal from the satellites (>28dB-hz) to download the required ephemeris data, you can read more about TTFF here. Now let's take a look below at what story the raw tracks have to tell us.

Green : Royaltek RBT-2010 - Blue : BT-359 - Red : BT-338

The BT-338 is off to a bad start in the wrong street but catches up, the BT-359 and RBT-2010 are spot on

For reasons unexplained, both the BT338 and BT359 "overshoot" on this sharp bend, likely the impact of working with very low and bounced signals as the SiRFstarIII chipset does. This impact is hard to predict and true to form the RBT-2010 does not display this...

...but a few moments later, the RBT-2010 veers off track following a brief stop at a light that the BT-359 handles much better staying spot on.

A few days later in the small streets of Nogent/Marne, note the "hiccup" bottom right.

Here again the BT-359 stays right on track while the RBT-2010 came in the bend too much to the right and then backtracked to come back on course

Taking a look at the signal analysis now we see the three receivers performing similarly in terms of no lost fixes and average number of satellites in the fix but with the RBT-2010 showing some higher dB-Hz numbers, which is either due to a more sensitive antenna or to some different tuning performed by Royaltek. We've seen above that this does not always have a postive impact


So now that the BT-359 has arrived it does not disappoint even though following up on the BT-338 was a tall order. No question that the design is much slicker which is a nice bonus and convenient too since you can now slip it into your shirt pocket. The more advanced power management, preserved battery life and performance are good news too. The slight disappointments that Globalsat has no control on are the marginal advances offered by the SiRFstarIII "v2" single chip package in terms of power use and negligeable in terms of performance (it does appears to handle multipath better in some cases though), but the bar had been placed very high with SiRFstarIII v1. This might become an issue with the arrival of the high performance v4 firmware on the ultra low power Nemerix NJ1030 chipset.

The BT-359 is not widely available at this time but early adopters can get it from Globalsat USA or Semsons (10% off for GpsPasSion Club members) who both ship internationally.

If you have questions or comments, you can use this thread of the forums

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