Radio interference

[Stanislav Silnitskiy]

Hi all!

Today I run tests in a public place (some Art Design College) and it looks that radio environment, that exists in the place, kills nrf51 completely.... My guess - terrible radio noise. As I could observe, they use Motorola AP8132 or something similar with 6 antennas. Two APs in the room 10x10 m.

As soon as I start scanning (sd_ble_gap_scan_start), beacon hangs. If I implement a watchdog, it is constantly rebooting.

So three questions, if anybody got in same conditions:

1. Are there any special tuning available inside nrf51 to work around such interference?

2. What is best scan params (ble_gap_scan_params_t) to avoid hanging the beacon when it scanning?

3. How can I debug this mess over SWD? (namely, with help of openocd)

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I also have to report, that for convenience reasons I use telephone cord wire (4-wire) to power beacons and have a terminal connection with them (up to 10 meters). So, sorry stupid assumption, is there any chance, that these wires can act as a degradation factor of environment for the chip?

[Øyvind Karlsen]

Hi,

First off, does your beacon work properly in other places?

1. BLE implements channel adaptivity, this means that if it sees interference in any of the 40 radio channels it utilizes it will automatically blacklist that channel and utilize the other available channels. It is very unlikely that you have noise that is blanking the entire band especially if the only source of interference is a WiFi access point. As a side note: if you are interested to see which channels are used by the WiFi in your area you can use an app like Wifi Analyzer.

2. Scan parameters should not impact wether your device hangs or not.

3. Be wary of what error codes you are getting when you call sd_ble_gap_scan_start.

It is unlikely that your telephone cord is an issue, there are some corner cases I can think of where this would be an issue:

• High power radio transmitters nearby (AM/FM base stations) can cause interference in the cable if it is unshielded
• Power failure due to breach in cable

Best regards,

Øyvind

[Stanislav Silnitskiy]

Hi Øyvind, I checked other apps and they work (of course!)... It was a stupid mistake in my own code, hitting infinite loop when I receive an adv. packet from "foreign" beacon/device. Thank you!