Friday, 11 January 2008

Bluetooth Power Classes

A question that I frequently hear people asking when it comes to purchasing a Bluetooth product is "do I need Bluetooth Class 1 or Class 2?". In this this post I will describe the different Bluetooth power classes and what class you should select when you next purchase a Bluetooth product.

For a start, I should make it clear that Bluetooth class 1, class 2 and class 3 all refer to Bluetooth power classes, not to be confused with Bluetooth device classes.

The following table compares the available Bluetooth power classes:

ClassMaximum PowerOperating Range
Class 1100mW (20dBm)100 meters
Class 22.5mW (4dBm)10 meters
Class 31mW (0dBm)1 meter

The actual range for each power class may vary depending upon environmental factors where the Bluetooth device is used. Class 3 devices have a very limited range and not very common, hence, they will be ignored for the rest of this discussion

So which power class should you choose for your new Bluetooth product? The two most important question that should be asked here are: "over what distance do I need my Bluetooth devices to operate?" and "what is the power class of the other Bluetooth device I want to communicate with?" Here are the two important pieces of information that you need to understand:
  • If you wish to communicate over the 100m range, you will need a class 1 Bluetooth device at both ends.
  • If you wish to communicate over the 10m range, you can have a class 1 or class 2 device at both ends.
Many people make the mistake of believing that they can extend the range of their class 2 device to 100m by purchasing a class 1 device for the other end. This is simply not true. Consider two people standing 100m apart, if person A yells loud enough for their voice to travel over 100m, person B will be able to hear what person A is saying, but if when person B replies they only yell loud enough for their voice to travel over 10m, person A will obviously not hear the response.

Hopefully this post has cleared up any confusion regarding Bluetooth power classes.


Anonymous said...

Thanks for the info... But wondering, how do you tell if the bluetooth device is class 1 or not, even if it says it's class 1?

DJ said...

I think you will just have to trust the manufacturers info. You can double check by looking at the power rating - 100mW or 20dBm for class 1. Hope that helps.

roni said...

contrary to what was said here i read somewhere else that all you need is a class 1 in one end in order to communicate 100m apart. i am not suer if that is true or not, but in my mind that was analogous to "if person A yells loud enough for their voice to travel over 100m, person B will be able to hear what person A is saying" and "when person B replies they only yell loud enough for their voice to travel over 10m" however person A also possesses the ability to also hear from 100m away (class 1) and will obviously hear the response.

so the question is, does a class 1 device able to transmit from 100m but not able to receive from 100m away? this requires further research but it makes sense to me that a class 1 device with a better antenna would be able to pick up transmissions from 100m away as well

Anonymous said...

Roni, you are not making sense. Of course a class 1 device can receive transmissions sent 100m away, but ONLY if they're from a device that is capable of transmitting that far, i.e. another class 1 device. The class isn't about how sensitive your receiver is (though it does come into account) but about how much power you transmit at. Skip the concern about whether you understood the analogy right and just trust that no device is going to receive a transmission from any class 2 or 3 device that is 100m away.

Anyway who cares - who is really ever more than 30 feet (10m) away from their BT device? Almost all BT devices are class 2 because 30 feet is a pretty good range. Sure there are use cases for needing to be much further away, but it's not a common use case. (If you need that, get yourself class 1 devices. :) )

Anonymous said...

Would be nice if I could find a class 1 bluetooth gps. Anybody know where I can get one?

Anonymous said...

I just posted about pairing Class 3 and Class 2 devices. I meant to say Class 1 and Class 2 devices.

Tiago Silva said...

It is possible, check the transceiver device sensibility, because, the transmitting power is different from the receiving sensibility, however, class 1 devices can deliver a lot more power than class 2 devices, they also "ear" a lot better than class 2 devices :) but this alone is not enough, you will need to add some more gain to the sensibility, that’s because that usb class 1 devices are not allowed to have very powerful buit-in antennas as they emit harmful radiation, but for experiments, open your Bluetooth adaptor, cut/scrub the PCB antenna off and solder an external antenna connector to the remaining PCB antenna path, then connect an antenna that fits your needs, since Bluetooth works in the same frequency range that Wi-Fi does, so, just get an Wi-Fi antenna! The more DBi's the antenna has the more sensible it will be and the more power it can radiate! You can get lots of posts around the internet about Bluetooth hacking with range extender antennas (just try an Interline 14DBi Patch or a Stella Doradus Dish set, don't go above the 20DBi antennas, they require lots of power and the Bluetooth class 1 devices can't handle, well, that much). Have fun delivering Bluetooth messages over 1Km or more loll ;)

william said...

Simple post but great expression of thoughts.. how do you do that? i think your a veteran blogger! am i right?

anyway I'm william
mind if I put a link back to you?

(clickable) ------> Black Tuxedo

Vivek Metange said...

thanks for providing such an useful information....!
-Vivek Metange

allan said...

thanks for the info but can i receive stuff from a class one device if my phone is only class two?

just_t_n said...

why don't you think about "GSM analogy"? The BTS tower antenna could broadcast till 5 Kilometers radius (with high power gain that's not safe if placed in mobile phone's). So the mobile phone use lower & safer power gain.

Imagine if our mobile phone should also transmit 5 Kilometers of power gain to reach the BTS tower. The battery will drain faster, the electromagnetic radiation will dangerous, but the advantage is : the BTS will have smaller antenna ^_^

just_t_n said...

I think bluetooth class 2 can communicate with bluetooth class 1 @100 meter range (range of bluetooth class 1). It's about transmission, and I've learn it at antenna's lesson :)

Anonymous said...

Does anyone know of a commercially available battery-operated class 1 Bluetooth SBAS (WAAS/EGNOS) GPS? The only one that I know about is the SXBlue and it's much heavier than what I need. The others that were in production when this post was created are no longer produced AFAIK.

Anonymous said...

Law of Reciprocity for antennas: If you can send a signal from antenna A to antenna B a distance "x", then you can also send a signal from antenna B to antenna A the same distance. The yelling analogy isn't realistic. However, you are correct that the range isn't 100m if one device is class 1 and one is class 2. Antenna's can't "yell" or "listen" specific distances, it is dependent on the power of the antenna it is trying to listen to or hte sensitivity of the antenna it is yelling at.

marc lester said...

where can i get an installer?

Anonymous said...

To anonymous re: GPS Class 1 Bluetooth.

Try Topcon Hiper SR. This is an SBAS and RTK enabled GPS with bluetooth that works over 300m (called 'Longlink'). It weighs only 0.85kg and is conpletely self contained.