RF noise connection issues between two NRF54L15

RE: RF noise connection issues between two NRF54L15

Menon — Tue, 17 Mar 2026 13:13:06 GMT

Hello,

Yes, this behavior is consistent with a collision scenario where the advertiser receives both a SCAN_REQ and a CONNECT_IND within the same receive window. Since the device cannot process both simultaneously, one of the procedures may be disrupted, leading to a failed connection attempt.

Configuring the advertiser as non-scannable removes SCAN_REQ packets from the equation, which avoids this overlap and improves connection reliability.

With extended advertising, this situation is addressed differently: scannable and connectable roles are separated, and the connection procedure includes an acknowledgment (AUX_CONNECT_RSP), allowing the central to determine whether the connection request was successfully received.

If extended advertising is not used, a similar effect can be achieved at the application level by leveraging QoS feedback after connection events. By monitoring whether packets are successfully received in the first few events, the application can decide to terminate and retry the connection earlier, rather than waiting for the controller’s default timeout.

Kind Regards,

Abhijith

RE: RF noise connection issues between two NRF54L15

nikeub — Tue, 17 Mar 2026 10:20:51 GMT

I can confirm that the issue disappears when I configure the advertiser as non-scannable.

Does this indicate a collision when the advertiser receives both a SCAN_REQ and a CONNECT_IND in the same receive window?

Is this a known issue? Can you investigate further and fix this on your end?

If this cannot be resolved, then since legacy advertising does not support undirected connectable non-scannable mode, the options seem to be either moving to extended advertising or handling this with retry logic at the application level?

RE: RF noise connection issues between two NRF54L15

Menon — Wed, 11 Mar 2026 07:52:21 GMT

Hello,

Could you check whether any nearby device, such as a phone, PC, BLE sniffer, or any tool is performing active scanning?

The issue might be related to the advertiser using scan response data, which means it is configured as scannable. If something nearby is actively scanning, it could interfere with connection establishment.

To narrow down the issue, please try changing the advertising mode to non-scannable (extended advertising) or directed advertising, and check whether the same issue still occurs. This may help determine whether the problem is related to the BLE procedure or to hardware/RF conditions.

[quote user="nikeub"]I don't have access on that old DevZone ticket you linked.[/quote]

I am not sure why the DevZone ticket I shared earlier could not be accessed. I will update the link again and share it here. Devzone ticket.

Kind Regards,

Abhijith

RE: RF noise connection issues between two NRF54L15

nikeub — Tue, 10 Mar 2026 13:29:18 GMT

I don't have access on that old DevZone ticket you linked.

But I did capture traffic when this happens now:

First a successful one where you can see the peripheral responds, followed by a failed attempt where RF noise? warning appears (BT_HCI_ERR_CONN_FAIL_TO_ESTAB).

Extract from pcap in wireshark:

1662	3.766076	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
1663	3.766701	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
1664	3.805002	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
1665	3.805629	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
1666	3.806138	c6:62:ff:50:5a:38	d8:8c:fc:c2:21:41	LE LL	60	CONNECT_IND
1667	3.807741	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1668	3.807971	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
1669	3.816491	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1670	3.816721	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	35	Control Opcode: LL_PERIPHERAL_FEATURE_REQ
1671	3.825241	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	35	Control Opcode: LL_FEATURE_RSP
1672	3.825543	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
1673	3.833991	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	35	Control Opcode: LL_FEATURE_REQ
1674	3.842741	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	28	Control Opcode: LL_UNKNOWN_RSP
1675	3.851490	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1676	3.851720	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	35	Control Opcode: LL_FEATURE_RSP
1677	3.860240	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	29	Control Opcode: LL_PHY_REQ
1678	3.860494	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
1679	3.868990	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1680	3.869220	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	29	Control Opcode: LL_PHY_RSP
1681	3.877740	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	31	Control Opcode: LL_PHY_UPDATE_IND
1682	3.878010	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
1683	3.886490	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1684	3.886719	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
1685	3.895240	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
1686	3.895469	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
// Lots of Empty PDUs removed for brevity...
2332	6.747886	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2333	6.756440	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2334	6.756635	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2335	6.765190	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2336	6.765385	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2337	6.773940	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2338	6.774135	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2339	6.782690	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2340	6.782885	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2341	6.791440	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2342	6.791635	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2343	6.800190	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2344	6.808940	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2345	6.817689	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	26	Empty PDU
2346	6.817884	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2347	6.826439	Central_0x2ccd10bd	Peripheral_0x2ccd10bd	LE LL	28	Control Opcode: LL_TERMINATE_IND
2348	6.826642	Peripheral_0x2ccd10bd	Central_0x2ccd10bd	LE LL	26	Empty PDU
2349	6.838940	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2350	6.839567	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2351	6.840077	78:2b:87:87:79:97	d8:8c:fc:c2:21:41	LE LL	38	SCAN_REQ
2352	6.840402	d8:8c:fc:c2:21:41	Broadcast	LE LL	63	SCAN_RSP
2353	6.874982	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2354	6.947456	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2355	6.948083	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
// Central sends CONNECT (but no response from peripheral...)
2356	6.948592	c6:62:ff:50:5a:38	d8:8c:fc:c2:21:41	LE LL	60	CONNECT_IND
2357	6.950196	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2358	6.958946	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2359	6.967696	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2360	6.976445	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2361	6.985195	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2362	6.993945	Central_0x141c5211	Peripheral_0x141c5211	LE LL	26	Empty PDU
2363	10.997653	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2364	10.998279	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2365	11.038178	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2366	11.038688	78:2b:87:87:79:97	d8:8c:fc:c2:21:41	LE LL	38	SCAN_REQ
2367	11.039013	d8:8c:fc:c2:21:41	Broadcast	LE LL	63	SCAN_RSP
2368	11.076078	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND
2369	11.076705	d8:8c:fc:c2:21:41	Broadcast	LE LL	61	ADV_IND

Attached pcap file:

devzone.nordicsemi.com/.../20260310_2D00_T132435.498122409UTC_2D00_capture.pcap

RE: RF noise connection issues between two NRF54L15

Menon — Fri, 06 Mar 2026 14:13:27 GMT

Hello,

I am not exactly sure what might be going on here. I found an old devzone ticket that discusses a very similar issue with the nRF54L15. I also recommend collecting sniffer traces and sharing them here so we can get more details about the issue. I am also checking internally to get more details on this.

Kind Regards,

Abhijith

RE: RF noise connection issues between two NRF54L15

Menon — Thu, 05 Mar 2026 19:34:44 GMT

Hello,

I am looking into this and will get back to you.

Kind Regards,

Abhijith