What is the top aid we rely on when evaluating a new GPS tracker? The answer is device “technical characteristics”. The specifications seem to be a great helper for choice making and selecting the best GPS tracker model. Usually, at the top of the specs list there is even a separate section dedicated to a GNSS module: the brand, supported navigation systems and sensitivity.
However, practice shows that most information taken from advertising materials and instruction manuals is of no use. Why? Firstly, because it is too general with sentences like “sensitivity: up to -165 dBm”. Secondly, it is a common trick among manufacturers to provide information on module or even chip parameters instead of revealing the real purchased item characteristics. Still, one must admit that even the best GNSS-chip just can not reach the stated criteria if it is connected to the wrong antenna or because of a power supply noise effect. In other words, various board components, design and the device assembly affect the final GPS tracker performance in a great way.
To find a GPS tracker that will meet your expectations we recommend to take a look at its internal structure: analyze functions of GNSS-antenna, the component layout on board, noise damping and, of course, its microprogram – the main regulator of all that.
GPS tracker PCB assembly’s special aspects that have to be taken into account:
Antenna size. In case a device works with built-in patch-antenna — the size of the receiver matters.
“The general built-in antenna size is 16mm x 16mm”,- says Ken Everett – the president of Australian GPS devices manufacturing company Digital Matters. For modules with a smaller antenna like CAM-M8 from Ublox it will be harder to get the signal.
The test results have shown that it is almost impossible to get the accurate location with such a module when standing inside a building, even when you are close to the window. To avoid this problem Digital Matters decided to install CAM-M8 into GPS trackers which are used for open-air working.
Those manufactures who possess a solid knowledge of R&D also suggest other even more sophisticated solutions. For instance, in Queclink (the OBDII tracker revised version) a manufacturer has installed even two orthogonal GPS antennas.
According to Ruslan Yusupov (a member of Loccate company), the suggested Queclink “know how” is a very up to date solution for GPS trackers of such a form factor. Devices of this kind are usually put under a steering tube where the signal is not so strong. Besides, it is not possible to change the GPS tracker location as the diagnostic port connector is fixed. That is why two antennas is indeed a great engineering solution.
Coming back to the size, Queclink professional staff assures it matters:
Different antenna size have different gain. Generally speaking 18*18*4mm patch antenna gain is around +2dBi while 15*15*4mm patch antenna gain is around +1dBi. Of course the ground plane will affect antenna, so for each project we customize the GPS antenna. The antenna vendor will tune the antenna to the correct resonate frequency according to the ground size. After tuning the gain between different models is less than 1.5dB when using the same size antenna. The sensitivity in our spec is under conducting test, not including antenna factor.
Antenna position matters! The whole device productivity can be significantly improved if its antenna is set up in a board correctly especially when dealing with small devices. Besides, there should always be enough space around the receiver for it to get and keep the max signal strength. As an example we will take two devices: Digital Matter Remora and Wonde Proud M7.
According to Vilius Cepulis, Business Development Manager at Teltonika, their engineers pay close attention to the position of all the elements on the circuit board at the initial designing stage.
Teltonika’s R&D has a long term experience in GSM/GNSS trackers PCB designing. Therefore we know how to prevent mistakes at the initial PCB designing stage. First important step is right placement for each component on a circuit board. With high-level measuring instruments in our laboratory, we’re always adjust both analogue and RF circuits on products prototype stage. Every time we aim to make small and easy to produce devices. Nevertheless, we highly care about GNSS quality and always keep enough space for high-gain GNSS antenna which is the essential part for our trackers. In result it allows us to deliver better reception tracker that are usually smaller than others on market.
Manufacturers sometimes place instruction notes on a GPS-tracker case about how the device has to be placed like “this side up”. It is better to ask clients first to look through such recommendation notes.
Noise damping. When choosing a proper component layout there is one more thing to consider: GPS-antenna should be isolated from high-frequency noise elements.
When talking about a high quality assembly we can not avoid mentioning a low-noise amplifier for GNSS-signal and SAW filters that block cellular signals so that they do not dampen the satellite ones. One should also take into account the fact that different combinations of low-noise amplifier and band pass filter can give contrasting results! The correct combination of the two elements is specific to advanced manufacturing products as it helps to reduce “cold start” time up to two times.
Having a solid firmware is a great help!
A device gets “smart GPS-tracker” title not only for its modern hardware but also for wisely installed software.
Assisted GPS. A GPS receiver may require 2-3 minutes to calculate the location point at the “cold start” time – the first switch-on of the device after a long shutdown. The best modern GPS-trackers are able to download the necessary voluminous information not only from satellites, but also through the mobile Internet – this is a technology principle Assisted GPS is based on. As the data transmission through cellular communication is much faster, the “cold start” does not take that much time but just a few seconds.
In practice, Assisted GPS (or simply A-GPS) gives a more defined track line at the GPS tracker switch-on moment or at the time when a car leaves the deep underground parking, etc. The usefulness of this function in portable trackers working in an interval mode is undeniable as their task is to quickly fix a location and manage to transmit it to the server within a few “wake up” minutes after hours or a long “sleep”.
Assisted GPS is realized in almost all modern GPS chips. However, there are still GPS trackers manufacturers that do not implement this technology in their firmware.
LBS or Cell-ID location. When tracking valuable assets it is useful to have a backup method of geolocation in mind (for instance, using cell towers). For this purpose, information transfer about the base station parameters should be realized in the GPS firmware connected to the required base station (MCC, MNC, LAC, CID). Thought, not all GPS-trackers have this function. When choosing devices that have involve it we recommend to pay attention to the number of base stations: the more there are, the more accurate triangulation tracking will be.
5 tips to choose wisely
Summing up, we can state that GPS-tracker parameters stated at advertising brochures give just a sketchy information that can not give us any full understanding of how the product will really work. The most important points to be considered are hidden underneath. So it is better that before the purchase you ask questions or ask for a sample to make field testing and take a look inside the product.
Here are our recommendations:
1. Do not rely solely on data from the manufacturer advertisement materials. See for yourself how the chosen GPS tracker works.
2. Test the product functioning exactly under the conditions in which it will be used by your customers: when the device is hidden under the car dashboard or located in boxes with cargo.
3. Pay attention to the “cold start” time (TTTF), the presence of “white spots” on track lines after leaving tunnels and exiting subways, estimate the track accuracy when going straight and in turns.
4. Make sure that the manufacturer implemented Assisted GPS and Cell-ID functions in the tracker firmware.
5. Look at the board of the compared GPS devices: estimate the built-in antenna size and the elements placement around it.
It is well known that when choosing a GPS-tracker having the similar functionality and a less expensive price one assumes the certain risks. In the highly competitive GPS trackers market it is hardly possible that you “overpay for the famous manufacturers brand”. It is more likely that you will pay for wise engineering solutions based on the manufacturer’s rich experience which, in the long run, will result in appreciation and loyalty from your customers.
The article was written by Navixy specialists and is based on a solid experience in integration and testing of hundreds of GPS-trackers models from the world manufacturers. More than 1000 models support allows you to easily make different suppliers device testing.
Timofey Temlyakov Posted on July 25, 2017