G-Sat BT-328 Review

by: Dale DePriest - all rights reserved.

This is the smallest and lightest BT GPS receiver available from GlobalSat. GlobalSat is a Taiwan company that has now established a US web presence under the name US GlobalSat. The products generally show a G-Sat name but may also appear with a house brand. This unit breaks some new ground although not as a high tech device. That acclaim would go to the previously released BT-338. The BT-338 and the BT-328 are pictured below along with an earlier successful unit called the BT-308. (The Mobile Crossing unit is one of the latest and best of the BT-308s due to its firmware revisions.)

This review is really about positioning the BT-328 in the family of products. If you just want the latest technology you might prefer the BT-338 which was a technical break through when it came on the market sporting the newest SiRF III chipset. However it tends to be pretty expensive and power hungry and these traits are exactly where the BT-328 shines while offering excellent performance. The next view shows how thin and small the BT-328 is as compared to the other two units.

It weighs in at about 2.5 oz and is only about 5/8" thick. It could easily be placed in a hat, such as the Tilley, for hiking use. For comparison the BT-338 is 3 oz and the BT-308 is 3.5 oz. Much of this weight is due to the battery and the BT-328 manages to work for over 16 hours on its small rechargeable Li-Ion battery. This is nearly as long as the battery on the BT-338 and 7 hours longer than the BT-308. In my actual tests on the BT-328 the battery lasted about 17.5 hours and could be recharged in 3 hours.

Performance

The G-Sat 328 uses a SiRFII GSC2 chipset. There isn't much information on this chip outside the Global Sat web site. However, I believe this is a new version of the SiRFII XTrac product. The XTrac product was originally a prelude to the SiRFIII chipset design and pioneered some of its features. Most notable is the ability to track satellites at a very low signal level. This improves performance in difficult reception areas like mountains, forests, and urban canyons although it does open the door to some multipath issues. The specs for sensitivity on an XTrac product are:

GlobalSat specs the sensitivity at -155 dBm which would relate to its tracking ability. The BT-338 advertises -159 dBm.

These are the approximate values I saw on this unit as shown in its NMEA messages. The effect is that the initial acquisition is similar to a standard SiRF II device (BT-308) which generally needs 28 dB-Hz or more to acquire and will track down to about 26 dB-Hz. The big difference of the XTrac is the ability to track down 16 dB-Hz. Practically this means the fix you get after turning it on will behave the same as another SiRF II device but while traveling you will have less lost fixes due to tree cover or other causes.

Open sky fixes would generally be within 40 seconds after you first turn the unit on which is good performace. The specs claim a cold start (no ephemeris and no almanac data) to be 42 seconds but I never experienced that. The best I saw for a cold start was 1 minute 15 seconds and sometimes it was more like 3 1/2 minutes while stationary. By the way, these are actually very good numbers even if they don't live up to the spec. Competing products are often in the 5 to 7 minute range for a cold start.

Cold starts on the older BT-308 are automatic. The unit tries to get a fix for 5 minutes and if unsuccessful it throws away the Almanac and does a cold start which generally takes another 5 minutes. The idea is if you move several hundred miles the unit will eventually figure this out by itself and perform a cold start. This generally works well for the user unless they tend to park in a garage or other place where a fix cannot be obtained in 5 minutes. If the user has difficult reception conditions this auto recovery can be very annoying.

The BT-328 does not do a cold start automatically. If you move a few hundred miles between fixes it may never get a fix. You can force a cold start with the included GPS Info program or you can wait until the battery runs completely down to force a cold start. While you probably don't move that much between fixes most of the time I still consider it a limitation particularly since it takes a really long time to run the battery down. I think a change to the power button sequence would be the solution. For example holding the power switch down for 10 seconds could be sensed and used to force the unit to go a complete reset, i.e. switching to NMEA mode and forcing a cold start.

The program GPS Info is included on the CDROM to facilitate a cold start and to provide a test program. The install provides both a PC version and a PPC version. Some folks have reported that PPC version of GPS Info will not allow the correct COM setting for some Bluetooth implementations on newer Windows Mobile 5 devices. It tries to be smart and detect the BT entries but sometimes fails which makes it worthless on those PPC devices.

Mac users will also find a test utility on the latest CDROM but I did not test it. Both programs can also be downloaded from their web site.

Hook Up

The BT-328 has a built in wireless serial capability using Bluetooth with a range of up to 30 feet (class II device). The manual says the baud rate should be set to 38400 but my experience says it will work fine at any baud rate from 4800 to 57600 or even faster if your software can keep up. This simplifies its use with programs that do not have an adjustable baud rate. The unit does support secure Bluetooth connections using a passkey of 0000.

The unit provides 3 lamps to indicate the state of the unit. The Blue lamp flashes slowly to indicate that BT is on and more rapidly to indicate a connection. The Green center light indicates power to the GPS module in NMEA mode and will blink when the GPS has a fix. The third light shows the status of the power charger or battery. The power button is sensed by the unit when you press it for a second or so. This unit will turn itself off if running on batteries and the Bluetooth signal goes away for 10 minutes.

The GPS will work with any computer that supports Bluetooth. It is particularly suited for PPC, WinCE, and Palm devices which have lots of programs that will work with a GPS. Many Smartphones can also use this GPS. It is also well suited to hook to Bluetooth enabled laptops.

Final thoughts

This is a good inexpensive solution in a wide variety of applications. In particular it is suited for automotive navigation and outdoor applications where rain or water isn't a factor. It can be placed in a zip lock bag if you need it to be waterproof. I found it maintained a lock under many conditions where other units would fail. I did not see any significant problems with drift even under difficult reception conditions.

Pros

Cons

revision
2006-Aug 30 - Original version