Most people imagine Bluetooth beacons transmit equally in all directions. However, this isn’t usually true. The 2.4 GHz frequency that beacons use is easily blocked or affected (through electronic resonance) by items such as the casing, the battery and even the printed circuit board itself. Also, the design of the antenna, that’s usually etched onto the printed circuit board, causes the transmission to vary depending on the direction.
Printed Circuit Board (PCB) Antenna
The above 2D design leads to different radiation depending on whether you are viewing face on, sideways or end on. The following diagram from a very informative Cypress article (pdf) demonstrates how the radiation pattern can vary in the x y and z planes:
In practice, it’s best to perform tests to assess how the beacon radiation changes with beacon orientation. You can do this by measuring the change in RSSI as you orientate the beacon. You can measure the RSSI using an app such as nRF Connect.
For example, with the long 300m range iB003N-PA, we determined experimentally that the best range was when the non-battery face of the beacon was facing the observer.
iB003N-PA – Strongest signal for us was downwards in this photo
However, this was for our particular scenario. How and where the beacon is mounted can also affect transmission and hence range.
So, the next time you are testing the range or installing beacons, take some time to assess how the beacon orientation might be affecting the range.
The batteries in the beacons we sell can last from months up to 7+ years depending on the beacon, battery size and type.
While the latest power efficient SoC beacons can make more of the available battery power you might want to consider not using batteries at all so as to ease maintenance.
Our USB powered beacons run from any USB socket and can be plugged into other hardware such as desktops or used with any inexpensive plug-in mains USB power supply available for a few pound/dollars/euros. However, as mentioned in a previous article, the location of the antenna so close to the desktop or power supply can cause the range and Bluetooth radio signal spread to be compromised. Look out for beacons that solve these problems by using an external dipole antenna.
The Bluetooth (Class 1) standard has a maximum output power of 20dBm. (Read our article for explanation of power). Many beacons don’t use this maximum as it would quickly flatten the battery. Most only allow up to +4dBm, +6dBm or +8dBm. In most cases battery beacons are set to operate at 0dBm. An advantage of USB powered beacons is that they can emit more power than is practical with a battery. For example, the iB005N-SMA reaches up to 130m. Watch this space for a USB beacon, coming in the next few weeks, that will have a range in the order of km rather than m.
Back to battery-based beacons, if you still need to use them, you can optimise battery use by using the right beacon settings and by measuring real-use battery drain. If you need help, consider a feasibility study.