Reception levels of BLE Signals

[RichardHdrd]

Dear Ladies and Gentlemen,

We have recently started comparing the BM833 (and the corresponding nordic devkit nrf52840) with an other hardware (ESP32), neither uses amplified antennas.

These exist as peripherals, both in our own hardware PCB. All tests are performed at identical distance between central and peripheral. Results also show similar results at 1MBit and Long-Range 125k coded PHY.

We used the following setups:

1) one self-created central hardware with BM833A, our nrf52840 DK as central and a smartphone using the nrf connect software (as scanner).

When we receive signals from ESP32 PCB peripheral, sent at level 0 dBm, we se an average RSSI of ca. -60, on all centrals (smartphone, nrf52840 DK central, BM833A central)

When we receive the signals from BM833 PCB peripheral, sent at level 0 dBm, we se an average RSSI of ca. -70, on all centrals (smartphone, nrf52840 DK central, BM833A central)

2) We changed the nrf52840 DK now to be used as peripheral, so we had smartphone and BM833A as centrals and nrf52840 DK, BM833 PCB and ESP32 PCB as senders.

When we receive signals from ESP32 PCB peripheral, sent at level 0 dBm, we se an average RSSI of ca. -60, on all centrals (smartphone, BM833A central)

When we receive the signals from BM833 PCB peripheral, sent at level 0 dBm, we se an average RSSI of ca. -70, on all centrals (smartphone, BM833A central)

When we receive the signals from nrf52840 DK peripheral, sent at level 0 dBm, we se an average RSSI of ca. -70, on all centrals (smartphone, BM833A central)

So, we observed a difference of averagely 10dBm in RSSI when sending at 0dBm.

We also tested other sender dBm settings (-4, +4) on the peripherals and saw corresponding changes in the reception RSSIs. The higher dBm values made the gap smaller (difference: ca. 5dBm).

Now the question is: where does the difference in RSSI values between the ESP32 peripheral and the BM833 peripheral (which matches the values observed when using the nrf52840 DK as peripheral) come from?

The hardware setup for BM833 PCB peripheral seems correct, as we see similar results when using nrf52840 DK as peripheral.

We built our (beacon-emitting) firmware based on the provided examples from nordic (central/peripheral).

Is there some unpublished call to activate extra antenna amplification or similar, that we are missing?

Best regards,

Richard

[Simonr]

Hi Richard

Can you share some HW details about the BM833 PCB and the ESP32 PCB you're using for comparison here? This seems mysterious indeed. Are you certain the ESP32 doesn't have any gain at all, as 0dBm for a device should be absolute and the same exact output power should result in very similar RSSI values even though it's not the best way to measure sensitivity. 

Do you have a spectrum analyzer so that you can measure the actual TX power of the devices you've tested out here?

Also, have you done any tests at different distances to see if one drops the connection faster than another or if it is basically similar.

Best regards,

Simon