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Comment by askvictor | Hacker News Reader

What's the difference in signal strength between bluetooth and wifi? I had assumed since they use the same frequency, and usually the same chip and antenna, they would be much the same (perhaps there are regulatory differences between them?) If anything, I'd guess that BLE would be more useful in this case as there is less handshaking, which means on a very poor connection you've got more of a chance of getting some data through.

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Depends on the Bluetooth device class.

Most devices are Class 2, with a maximum transmit power of only 2.5 mW; that's not a lot compared to Wi-Fi's ~20-30 mW.

AirPods are notably Class 1, which goes up to almost 20 mW! They accordingly have much better range as a result.

Bluetooth LE in newer version has new low-bitrate coding methods to allow for even greater ranges (called "Coded PHY"). Assuming Bluetooth LE classes are the same as for EDR (I don't know if they are!), this source [1] claims a 4 times greater range using coded PHY, which would be in the range of several hundred meters.

[1] https://www.bluetooth.com/blog/exploring-bluetooth-5-going-t...

> I had assumed since they use the same frequency, and usually the same chip and antenna

Yes and no. Bluetooth is 2.4GHz, WiFi has many bands, including one around 2.4GHz. Those can share an antenna, but I think that means only one can be sending at a time (they could mix the signals, but I guess that would mean connection would fail for the less powerful Bluetooth signal)

https://en.wikipedia.org/wiki/Bluetooth:

“It employs UHF radio waves in the ISM bands, from 2.402 GHz to 2.48 GHz”

https://en.wikipedia.org/wiki/List_of_WLAN_channels:

“The 802.11 standard provides several distinct radio frequency bands for use in Wi-Fi communications: 860/900 MHz, 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 5.9 GHz, 6 GHz, 45 GHz and 60 GHz. Each range is divided into a multitude of channels. In the standards, channels are numbered at 5 MHz spacing within a band (except in the 45/60 GHz band, where they are 0.54/1.08/2.16 GHz apart), and the number linearly relates to the centre frequency of the channel. Although channels are numbered at 5 MHz spacing, transmitters generally occupy at least 20 MHz, and standards allow for channels to be bonded together to form wider channels for faster throughput.

Countries apply their own regulations to allowable channels, allowed users and maximum power levels within these frequency ranges. The ISM band ranges are also often used.”

FWIW I was referring to 2.4GHz Wifi, which shares is basically exactly the same frequency range as bluetooth (14 Channels in 2412-2484MHz vs 80 channels in 2400-2483.5MHz). The devices I've been working with share a chip and antenna, though they can't typically do both at the same time without multiplexing.

I'm interested in, for this particular problem (finding a device using just wifi or bluetooth), which one would have the greater effective range.

I've been using three AirTags and two of the cheaper clones mentioned above. I can activate both about 100m away in the forest, if there is a line of sight.

On the other hand, i can walk an entire day through the forest (with some other people around every now and then) without a single position update from the tag.

> What's the difference in signal strength between bluetooth and wifi?

Big in my experience. 15 - 20 feet vs 100+ feet for wifi out in the open like that.

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