After hearing reading a lot of positive feedback on the Garmin GLO, I decided to get one and compare it with my QStarz 818XT which has worked perfectly for me over the past year. My primary interest in the GLO is to see whether it can provide faster updates and more accurate positioning information.
The Garmin GLO and QStarz 818XT are bluetooth GPS receivers and can be used to provide a much more accurate GPS signal for race track timing compared to the built-in GPS found in most mobile phones. The GPS in a mobile phone won’t typically update its position more than once a second (1Hz) while these units can update at up to 10 times per second (10Hz). I use RaceChrono to record my lap times and if you are new to this, you can find out how RaceChrono works in this detailed post on using RaceChrono.
Both of these bluetooth GPS devices are similar in size although the Garmin is slightly slimmer and longer than the QStarz-818XT. The battery in both is good with each device giving a minimum of 12 hours on a single charge – enough for a full day on track. In fact the battery life of the QStarz is actually a lot better than the GLO, supposedly lasting up to 40 hours (although I haven’t actually proved that).
Size and battery life isn’t the only difference between these two units – the technology used by them for determining their position is also different. The QStarz-818XT only uses the US GPS satellites in order to determine its position while the Garmin GLO uses both the US satellites and the Russian GLONASS system. This makes the GLO’s hybrid technology fairly unique in the market compared to most other makes and model of GPS unit, and it’s what gives the GLO an edge over the QStarz in terms of outright accuracy.
This image is from RaceChrono showing the satellite information when connected to the QStarz-818XT. You’ll notice how the GPS unit has locked on to 7 satellites and is reporting its horizontal position accuracy as 1.1 – this is an excellent value indicating a high degree of precision.
The DOP values range from 1 to more than 20 where 1 is ideal, 1-2 is excellent, 2-5 good and values over 5 less increasingly less accurate . DOP stands for dilution of precision and you can get a detailed description of DOP values from Wikipedia.
Because the Garmin GLO is able to use both the US GPS and Russian GLOSNASS satellites for determining position, it has access to more satellites at any point in time which in theory allows it to determine its position more accurately. Under the satellite settings it reports its horizontal DOP as 0.7 which means greater accuracy than the 1.1 DOP value reported by the QStarz. This makes sense because the GLO is reporting a fix from 14 satellites compared to the QStarz’s 7 satellites.
To get these screenshots of RaceChrono, both GPS devices were placed side by side with each connected in turn to RaceChrono to grab the two screenshots. The two readings were therefore taken within a few minutes of each other and so should not really be affected by the fact that the satellites will have moved slightly during the test.
Startup times and operating speed
My feeling is that while the Garmin GLO gets its first fix a little faster than the QStarz-818XT there really isn’t that much in it, and since both devices lock on to satellites so quickly – you’re never stuck waiting for the first position fix. Both devices were also really easy to connect to RaceChrono running on my Android phone.
One major difference is the position output frequency of the devices. The QStarz is able to operate at 1Hz, 5Hz or 10Hz while the Glo only operates at 10Hz* – this means that it will send an updated position fix (over bluetooth) ten times a second or every 1/10th of a second.
While the QStarz-818XT is also able to operate at 10Hz, it will not output as accurate a signal as it will at 5Hz where the DGPS (differential GPS) capability can be enabled. In fact, the general consensus is that it is better to run the QStarz at 5Hz because although you only receive a new position fix five times a second each fix will be more accurate fix that the ones received at 10Hz. I’ve written another post that describes how to configure the QStarz-818XT to operate at 5Hz.
* When running RaceChrono with some Android 4.0+ devices using the Garmin GLO, the output frequency can switch from 10Hz to 5Hz and sometimes even down below 1Hz. This isn’t a problem with the GLO so much as a problem with the bluetooth stack in Android 4.0 and above. The device is sending too much data too fast for the OS to be able to process because some genius programmer decided to rate limit the receiving side of the Android bluetooth stack!
My first impressions of the Garmin GLO are good. The unit is smaller than I through it would be, and it operates well with RaceChrono. It ships with a USB and a separate cigar charging lead which is good. The one thing I don’t like though is the On/Off switch which is too easy to knock. You could pack the unit away and find that the battery flat when you needed to use it because the On/Off switch got pressed by mistake in transit.
The QStarz-818XT is a solid performer. I’ve never had any problem with my unit. It locks on to satellites quickly and operates flawlessly at 5Hz with the DGPS enabled. I like the long battery life and the fact that the On/Off switch requires a more positive sliding action to switch it on or off which means that it’s unlikely to be switched on by mistake.
In my next post, I compare the operation of these two bluetooth GPS receivers on the race track.