Very short radio range issue when using the rRF52840 modules

[Nicholas Lee]

I have developed two PCBs that each use the rRF52840 chipset in the form of the BL654 modules from Laird which include PCB antennas.

I based the software project on the Nordic UART demo, and the only change to the radio parameters I have made is to increase the data packet length to the maximum permissible and a sending a packet every 20ms, in both directions.

I get a nice reliable data connection with no packet loss between the two boards on the bench, but the connection drops out at a range of 6.5 metres.

This seems very short to me as I was hoping for at least 50 metres or so, with the default project settings.

Can you assist me with finding out what the fundamental factor is that is limiting the range, and how to resolve it? Thanks.

[Marjeris Romero]

Hi Nicholas,

What output power are you using? Are you testing in a open enviroment or are there many obstacles between the two devices that may result in loss and reflections in the RF path?

Best regards,

Marjeris

[Nicholas Lee]

The output power is whatever the default is as set by Nordic's own example project code.
I haven't modified it, and I don't even know where the setting is located to change it.
I'm going to assume that their project sets it to 0dBm which apparently is the softdevice's default.

The measurements were taken with the two transponders 1m above the ground.
I placed one transponder on a waist-high brick-wall, and walked away from it holding the other transponder until the connection dropped out. The ground surface was gravel. There were no line-of-sight obstructions other than the product's plastic enclosure.

[Marjeris Romero]

Hi,

I am sorry for not getting back to you sooner.

This seems very short to me as I was hoping for at least 50 metres or so, with the default project settings.

I think 50 meters is a bit unrealistic for 0dbm output power mode indoors. You can play around with the Bluetooth range estimator to calculated the expected range between two bluetooth devices here: https://www.bluetooth.com/learn-about-bluetooth/key-attributes/range/#estimator

For 1M PHY and 0dbm transmit power the expected range indoors in an office will range closer to 15-19 meters. Office are usually high interference enviroments.

the only change to the radio parameters I have made is to increase the data packet length to the maximum permissible and a sending a packet every 20ms, in both directions.

Longer packets will also have less change of being delivered correctly, which can end in multiple retransissions and connection loss if the packet loss is too big. You can try to decrease the packet length and see if there is any difference.

You can change the output power to +8dbm in your project calling sd_ble_gap_tx_power_set().

We can also do a layout review of your custom PCB if you attach your files here for review. Things like the size of the ground plane on your PCB, placement of the module and keepout area around the antenna can affect the performance. See the PCB layout considerations in the module datasheet for more information.

Doing tests with and without the plastic enclosure could also a good idea to assess if the enclosure affects the performance in any way.

Best regards,

Marjeris