What are the advertising channels?

Channels 37 (2402 MHz), 38 (2426 MHz), 39 (2480 MHz), placed in Wi-Fi gaps. Each event transmits on all three for frequency diversity.

100 ms interval: ~80 microamp avg (2+ yr CR2032). 1 s: ~3 microamp (5+ yr). Random 0-10 ms jitter prevents collisions.

Wireless Protocols

BLE Advertising

Q: What is extended advertising?

BLE 5.0 allows 255-byte payloads via secondary channel chaining, up from 31 bytes legacy.

BLE Advertising is the connectionless broadcast mechanism where a device periodically transmits packets on three dedicated channels (37, 38, 39) to announce its presence, share sensor data, or enable connections. Legacy advertising supports 31-byte payloads; BLE 5.0 Extended Advertising supports up to 255 bytes via secondary channel chaining. It is the foundation of iBeacon, Eddystone, and all BLE device discovery.

Category: Wireless Protocols

Channels: 37, 38, 39

Understanding BLE Advertising

An advertising event transmits the same PDU on channels 37, 38, 39 sequentially (~0.3 ms each). The advertiser optionally listens for scan/connection requests, then sleeps until the next interval (20 ms to 10.24 s). A random 0-10 ms delay prevents repeated collisions between co-located advertisers.

ADV PDU types: ADV_IND (connectable/scannable), ADV_NONCONN_IND (beacon only), ADV_DIRECT_IND (fast reconnect), and ADV_EXT_IND (BLE 5.0 extended with secondary channels for larger payloads).

Advertising Power Budget

Average current:
I_avg = (I_TX × t_event) / T_interval + I_sleep

100 ms interval, 1 ms event, 8 mA TX:
I_avg = 80 μA + 2 μA = 82 μA total

Advertising PDU Types

PDU	Connectable	Scannable	Payload	Use
ADV_IND	Yes	Yes	31 B	Discovery
ADV_NONCONN	No	No	31 B	Beacons
ADV_DIRECT	Yes	No	0 B	Reconnect
ADV_EXT	Optional	Optional	255 B	BLE 5.0

Common Questions

Frequently Asked Questions

Advertising channels?

Ch 37/38/39 at 2402/2426/2480 MHz, placed in Wi-Fi channel gaps. Three channels provide frequency diversity.

Extended advertising?

BLE 5.0: 255-byte payloads via secondary channel chaining, up from 31 bytes legacy.

Interval vs power?

100 ms: ~82 μA (2+ yr CR2032). 1 s: ~3 μA (5+ yr). Random jitter prevents collisions.

Related Terms

← BLE 2M PHY BLE Channel Map →

BLE Beacons

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