Radio Interference

RE: Radio Interference

Andreas — Mon, 09 Dec 2019 11:09:08 GMT

Hi,

Your understanding is correct. When C is transmitting at 2MHz lower than B to A, it will block the signal from B to A if it is more than 22 dB stronger than the signal from B to A. Even if moving it 1.5m away from A, it will still be quite strong an potentially block a weak incoming signal. Your application has 5 MHz spacing, so you should refer to the line >3MHz

C/I_1MBLE,>3MHz

1 Mbps BLE mode, Adjacent (≥3 MHz) interference

-50

This is a typical spec for all channels. Based on your description A to B is quite 'far' away, the received signal strength is likely quite low, meaning the higher power from the C will be blocking, your conclusion is correct. You either need to make C keep quiet for longer, or even the signal strengths. You could also probably land somewhere in the middle by experimenting with acks and retransmissions.

Best regards,

Andreas

RE: Radio Interference

Peter_53 — Wed, 04 Dec 2019 13:11:53 GMT

Hi Andreas,

C is indeed close to A. It is on 10cm in one case and 1 - 1.5m in the other. We did not identify any big improvement in case we moved C on 1.5m from A.

Thank you for the quick reply. Just to be sure that I do understand the Rx selectivity table right. Rx selectivity tells us how many dBs higher can a blocker signal (C in our case) be comparing to out signal (A and B), right? So for example:

C/I_1MBLE,-2MHz

1 Msps BLE mode, Adjacent (-2 MHz) interference

-22

- In this case C signal must be 22dB lower than our signal, right?

- Is this the case when C signal frequency is 2MHz lower than A and B?

- How can I know which line in this table is referring to our case (what does -2 MHz, +2MHz, >3MHz means)?

Is the following conclusion correct: If the C is much closer to A, even though they are working on different frequencies, C will block the signal of B trying to send a message to A.

Thanks!

RE: Radio Interference

Andreas — Wed, 04 Dec 2019 12:28:30 GMT

Hi,

See the RX selectivity spec: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/radio.html?cp=4_2_0_22_14_5#unique_1710897161

It might be that C is positioned such that its signal power on either of the devices are ~50dB higher than the wanted signal between A and B, e.g. if C is right next to either A or B. How are these positioned and does it help to move C slightly farther away?

Best regards,

Andreas