Bluetooth Range Measurement and Recommendation for Deployment
Fresnel Zone and Bluetooth Range
When Bluetooth signal is reflected by a surface inside the first Fresnel zone, it arrives at the receiver out of phase with the direct Bluetooth signal and reducing the signal amplitude. If there is no obstruction inside 60% of Fresnel Clearance Zone radius, signal reduction is small.
Fresnel Zone radius and clearance for Bluetooth signal for various distance is listed below. When Bluetooth range was 10 meters, multiple path interference was not an issue. It is the major factor in limiting range of long range Bluetooth 5 transmission.
Scottsdale Arizona Test Site and Measurement Method
Bluetooth ranges are measured with antenna at 2 heights.
Low Multiple Path Interference (LMPI). Antenna height is set to at least 60% of Fresnel zone clearance when possible. Ranges at LMPI is related to link budget available, important for wall penetration when IoT devices are deployed indoor.
1.52 meters ( 5 feet, typical height of thermostat in the USA).
We measure one-way data transmission from a module with Master Codes to a module with Slave Codes. Range is the maximum distance that
Bluetooth connection can be maintained between Master and Slave module.
Valid data can be received by Slave module. Error packet is allowed.
On the first measurement, two antennas face each other. Slave antenna is rotated by about 30 degrees on the next measurement. Total of 12 measurements are taken. Bluetooth range is the average of these 12 measurements.
This test site is a straight dirty road without tree for 2400 meters. There are some low bushes in the last 800 meters.
Long Range Module Comparisons, 9/2018
Comparing ranges of long range Bluetooth 5 modules :
BT832F and BT832X Range Measurements, 9/2018
BT832F and BT832X measurement raw data are shown below. One way data transmission is measured.
BT832F-F column has data for BT832F TX to BT832F RX.
BT832F-X column has data for BT832F TX to BT832X RX.
BT832X-X column has data for BT832X TX to BT832X RX.
A few takeaways from these measurements:
BT832X with Power amplifier has small range degradation when Multiple Path Interference is high.
Low Noise Amplifier in SKY66112 receiver provides small (about 18%) range improvement.
BT840F and BT840 Range Measurement Results, 8/2018
In addition to LMPI and 1.52 meters, we measure BT840F ranges with antenna at 0.55 meters (21.5 inches), the height of USB840F dongle when plugging into an smartphone charger plugged into a wall AC outlet in the USA. This is for using USB840F as a Bluetooth signal repeater in a typical building in the USA.
"0" is antenna facing each other. "30" is the second antenna rotated clockwise by 30 degrees.
"ant. 5.2/4.2" is for one antenna at 5.2 meters and the other 4.2 meters above ground. "ant. 1.52" is for both antenna at 1.52 meters above ground.
A few take aways from these measurements.
Comparing Bluetooth ranges of 1Mbps and 125 Kbps at LMPI, the CODED-PHY receiver gain is 7.2 dB for BT840F. It is 6.8 dB for BT840.
BT840F antenna has the best gain at 30 to 60 degree angle. 3200 meters is the maximum range allowed at Scottsdale Arizona test site. There is a notch for antenna gain at 120 degrees.
At high multiple path interference, deviation of range at different angles is smaller. Or, antenna is closer to omni-directional. When an IoT device is inside a building, signal can be reflected from floor, wall, and ceiling, range deviation can be small.