i-Blue GM-2 USB GPS Receiver
Marvin Hlavac
Review: i-Blue GM-2 USB GPS Receiver by TranSystem (66 ch, MTK2, 5Hz, WAAS)

i-Blue GM-2 is a USB GPS antenna and receiver unit that was just recently (Sept. 2010) released by TranSystem Inc. The receiver is based on the MTK2 chip, whose tracking sensitivity is rated at very impressive -165dBm.

iBlue GM2 is, as far as I know, the very first USB GPS receiver based on the second generation of the MTK chip.

i-Blue GM-2

GM-2 refreshes at the rate of up to 5Hz (as opposed to the typical 1Hz). It is possible to switch to 1Hz via software. At the time of this writing, i-Blue GM-2 may actually be the least expensive GPS receiver offering 5 Hz refresh rate.

iBlue GM2 is waterproof, and it does have a magnetic base for easy mounting on the car's roof, if needed, but thanks to the receiver's high tracking sensitivity, it should work just fine on the dashboard, too.

i-Blue GM-2 Refresh Rate and Baud Rate Selection

Not all GPS navigation software applications are compatible with high refresh rate GPS receivers, and some will work only with certain baud rate(s). The version of GPSview software utility currently shipped on a CD with i-Blue GM-2 is able to change the refresh rate to your choice of 1, 2, 3, 4, or 5 Hz, but it lacks the ability to change the baud rate. But thanks to Ken, and his testing of the unit with various GpsView versions, now we can change even the baud rate:

Originally Posted by Ken in Regina

[...] older version of GPSView has the ability to change everything [...]
For everyone's convenience, the free old version of GpsView 1.2.2 has been attached to the bottom of this post.

GPSview v1.2.2 iBlue GM2 settings

Notice the two controls in the above screen shot that I highlighted in yellow color. The first one lets you set the iBlue GM2's fix update rate to 1, 2, 3, 4, or 5 updates per second, and the second one lets you set the baud rate to 4800, 9600, 14400, 19200, 38400, 57600, or 115200. Again, this is something you may not be able to achieve with the version of GpsView currently shipped with the GPS receiver, or currently available as a download at the manufacturer's web site. The working version of GpsView 1.2.2 is attached to this post. Scroll a bit further down to download GpsView version 1.2.2.zip.

With iBlue GM2 set to the baud rate and the refresh rate depicted on the above screen shot, I was using Microsoft Streets and Trips software with no problem at all. The same 1Hz and 4800 baud rate settings will be required for anyone wishing to use Microsoft AutoRoute, or Microsoft Mappoint.

If you wish to use Garmin Mobile PC software, change the GM-2's default 115200 baud rate to 38400, or lower.
Originally Posted by tcassidy

[...] I have confimed that Mobile PC will not find this GPS unless you set the bit rate (using GPSView 1.2.2) at 38,400 bps or less [...]
Garmin Mobile PC is software capable of taking advantage of refresh rates higher than 1Hz. At 5Hz the map movement is nice and smooth. Enjoy. And do let us know how you like it.

i-Blue GM-2 Test in Urban Canyon

i-Blue GM-2 v GlobalSat BU-353

i-Blue GM-2 (red) versus GlobalSat BU-353 (green)

I like to test new GPS receivers in extremely difficult environments, such as the urban canyons of downtown Toronto, where the weak signals from GPS satellites bounce off of the tall buildings, and the antenna is unable to have a clear view of satellites in many different directions. The center of the above map is where the tallest buildings are, and it represents the most difficult area for GPS receivers.

I did a side-by-side comparison of the new i-Blue GM-2 (MTK2 chip) and the older GlobalSat BU-353 (SiRFstarIII chip). All GPS receivers I have ever tested in this particular section of downtown Toronto, have struggled in a similar way. Surprisingly, the GlobalSat BU-353, based on the 5 year older SiRFstarIII technology, was not performing any worse here than the brand new GM-2. If you look at the screen shot above, you may actually conclude that the BU-353 worked even slightly better.

i-Blue GM-2 Specification

  • Lead-Free – RoHS/WEEE compliant
  • Tracks 66-Channel of satellites
  • Fast Position Fix
  • Low power consumption
  • LED indication for GPS status
  • Build-in re-chargeable backup battery
  • IPX7 waterproof
  • Magnetic base for easy mounting on the car
  • General: L1 frequency, C/A code (SPS)
  • 66 independent tracking channels
  • Tracking Sensitivity: -165dBm
  • Update Rate: 1, 2, 3, 4, or 5Hz
  • Accuracy Without aid:
    • 3.0m 2D-RMS
    • <3m CEP (50%) without SA (horizontal)
    • DGPS (WAAS, EGNOS, MSAS, RTCM): 2.5m
  • Acquisition (open sky):
    • Cold Start : 35 sec
    • Warm Start : 34 sec
    • Hot Start : 1.5 sec
    • Cold Start (with AGPS): <15 sec
  • Reacquisition < 1sec
  • Dynamic Altitude : 18000m (max.)
  • Velocity : 515m/sec (max.)
  • Acceleration :4G (max.)
  • Supply Voltage DC 5V
  • Power Consumption 40mA @ 5V / Tracking
  • Backup Battery Build-in
  • NMEA Message NMEA0183 v3.1 baud rate 4800/9600/14400/19200/38400/57600, default 115200
  • Selectable Output: GGA, GLL,GSA, GSV, RMC, and VTG
  • Datum Default WGS-84
  • Antenna Build-in 25*25*4mm patch antenna, right hand circular polarization, 50ohm
  • Mac support Yes
  • Connector USB type A male
  • Operating Temperature -30C to 85C
  • Storage Temperature -40C to 85C
  • Operating Humidity <=95%, non condensing
  • Dimension 57 x 64 x 16(H) mm max

If you wish to try a high refresh rate receiver, the i-Blue GM-2 is an excellent choice. Please post your feedback, if you've tested it yourself already.

Check your favorite retailer for availability and price. Usually sells for around $36.

Questions / Comments?
Attached Files
File Type: zip GpsView version 1.2.2.zip (492.4 KB)
That is where sensitivity can be a curse rather than a blessing. Looks like there is a need to do a little more work with the selectivity algorithms in this unit.

Marvin Hlavac
Yes, more sensitivity was not needed in the area where I tested the i-Blue GM-2 vs. BU-353. Both units had a fix on 6 to 7 satellites most of the time. The difference was how the signals were processed.

On the other hand, the improved sensitivity of the MTK2 chip likely resulted in the unexpectedly fast first fix when I received the i-Blue GM-2 package, and connected it to my laptop for the very first time in the family room at home. I was expecting to wait at least several minutes for it to start working, but to my amazement, it must have taken much less than a minute.
Ken in Regina
Yes, I was amazed at the time to first fix on the cold start, out of the box. This was at the kitchen table as I was trying to get the driver installed on my laptop. The GM-2 was connected to the USB port on my laptop as I was wrestling with getting the driver to work. The indicator light on it indicated it had a fix in hardly any time at all. I didn't time it .. never thought to .. but it was no more than a couple of minutes.

I had some problems getting the driver installed and working. I think it was having some problems with a couple of other USB-to-serial drivers that were already installed on my laptop, one for the BU-353 and the other for a real USB-to-serial cable.

To get it working I finally removed the driver supplied with the unit, plugged the unit in and let Windows go and find a driver for it. It worked fine after that. And ... guess what ... the working driver that Windows found and installed is also an older version.

Seems like this fancy new device has a serious case of nostalgia...

Ken in Regina
Regarding the sensitivity of the newer GPS chip technology ... the secret is not that they receive signals better. There was really nothing stopping the older technology from receiving weaker signals just fine.

The problem is that the more sensitive you make the receiver, the more problem you have with multipath signals, as you can see with Marvin's test in downtown Toronto. The manufacturers of the earlier GPS receiver chips did not have the necessary algorithms to sort out the prime signals from the echos bouncing around. That was about equal parts that the earlier algorithms were a little bit primitive and that the processing power to compute anything more complex and sophisticated was either too expensive or consumed too much power.

The newer chips benefit mostly from increased low-consumption computing power on the GPS chip which allows for more sophisticated algorithms to decide which signals to use and which to reject. This allows them to use more sensitive receivers. But the dB sensitivity spec is mostly a marketing thing, like megapixels on digital cameras ... once you get beyond a certain number, it may impress potential buyers but it's otherwise meaningless.

Then the trick is to know when more sensitivity (as in finding its location at your kitchen table) is important and when it isn't.

Ken in Regina
Well, the BU-353 finds its location at my kitchen table, too. As does my Nuvi 765T, my eTrex Legend HCx and both of my Bluetooth receivers. Shucks, if you leave it sit there long enough, even my creaky old iQue 3600 will eventually find itself.

But, yes, that is the point. The vast majority of current GPS devices on the market are sensitive enough to function pretty much anywhere you want to use them. As Marvin's test shows, more sensitivity is not necessarily an advantage in areas where there is a lot of multipath (reflected signals) like urban canyons. They may have some advantages out in the wilderness in real canyons and/or heavy tree cover where you are dealing just with weak signals rather than a lot of multipath. Unfortunately I did not get my evaluation unit in time to try it on my recent travels in the Rockies.

This GPS is certainly very fast to first lock as already stated. It obtained lock sitting on my desk before I could even get the driver installed. Per Ken's findings, I let Windows track down a driver for me rather than use the included CD. It installed fine on my Window 7 64 bit system.

On another note, I have confimed that Mobile PC will not find this GPS unless you set the bit rate (using GPSView 1.2.2) at 38,400 bps or less.

The driver, Silcon Labs CP210x USB to UART Bridge (v6.1) has a feature I like. You can plug the GPS into a different USB port and it will not install again. It will use the existing driver therefore maintaining the same COM port. This seems to be an uncommon approach these days.

I did see a warning about a serial mouse (an old problem) and I see it in Device manager as a non working addition, However, that did not affect the operation of the GPS.

Marvin Hlavac
Terry, is the v6.1 the driver that is included on the CD? I didn't need to install any driver at all, as the i-Blue GM-2 simply started to work w/out installing any driver (it used a driver that was already installed on my laptop).
The driver on your laptop was installed when you last used the iTrek M7; I know you once had one. You will probably find it is version 4.40 but whether the newer driver offers anything better, I don't know. I did not check which driver was on the CD but went staight to the automatic install after reading Ken's post.

The driver is not on the Windows update site but Windows offered to find it for me. I think that is a Win 7 feature but it might work on Vista as well. Both my XP computers already have the 4.4 driver on them so I would have to uninstall it to see how XP would respond. I'll check that out later.

USB to UART Bridge VCP Drivers

The version on the CD is 4.40 per the release notes.

I fired up my scatter plotter (a work in progress) and collected 24 hours of fix data from my GM-2. I connected it through two six foot USB extenders and placed it atop a ladder on my deck attempting to get it high and out of a multi-path environment.

WAAS was turned off. The GM-2 was operating a one fix per second sending at the default 115200 baud.

The position in the lower left of the plot window is the average of the fix locations and it agrees to within a few feet of the satellite image position of Google Earth. That's the best I can say about accuracy within the methodology of the experiment.

A CEP (Circular Error Probable) circle contains fifty percent of the fixes. It's fairly accurately calculated from the radius error histogram. For this run, that circle was only eight feet in diameter.

Oddly, the receiver reports position with six digits of minute precision i.e. 41 deg 03.589058 min or, less than an inch. Not that it matters but reporting that precision raises those arguments concerning the relationship between precision and accuracy. But, it renders the scatter plot as a 'Ball of Yarn'.

Magnetic Variation is not reported as indicated by the two empty fields in the NMEA GPRMC sentence:


--- CHAS
Attached Images
Great information! Would you have a BU-353 or other SirfStar III GPS to compare that with?

I thought I would try it on the UMPC (XP) as it did not show the driver CP210x in Add/Remove Programs as my main computer does. Unfortunately, it is there anyway and uninstalling it does not remove it from the computer.

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