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I have had some success connecting to my Bluetooth devices but only when I'm in the same room as the Rpi. This limits the utility somewhat... I had hoped to be able to use them anywhere in my home. I will (eventually) move the Rpi into a more central location, but I don't think that it will give me sufficient range.

I would like what seems to be 15-25 meters (max) through drywall/lumber walls on a single floor.

It's my understanding that the Rpi 3 does have an unpopulated antenna connector, but that this is only for the wifi (I use ethernet).

Are there any USB adapters that might solve this problem? The only ones I can find on Amazon are those low profile ones that stick out a quarter of an inch. I can't imagine those will be a superior option (probably just for keyboards/mice a few inches away?).

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  • What Bluetooth devices are you connecting? – CoderMike Nov 20 '18 at 7:06
  • @CoderMike For now, a blood glucose monitor. Soon, several others (blood pressure, bathroom scale). The bathroom scale may actually be close enough that it's not the issue, but the others I don't want to traipse to the other side of the house to use. It also somehow picked up my FIXD obd2 device in the car, which I didn't even know was on while the engine was off... might be interesting to be able to use that, though I don't think that's feasible really. – John O Nov 20 '18 at 7:10
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Bluetooth shares an antenna with WiFi, and for this reason Bluetooth on a USB dongle may have better range performance than the in-built BT antenna.

The other thing that will help is elevation. This is due to RF-propagation and laws-of-physics reasons unrelated to Raspberry Pi. But if you can put any antenna a little higher (on a shelf, mounted high on the wall or ceiling) it will reduce RF path loss, and thereby improve range performance.

There is also a possibility you may be able to change the transmit power from the command line. I have not tried this, so proceed at your own risk. Here are some references to get started:

  • Linux SE Q&A: How to set Bluetooth transmit power? has some ideas & avenues for additional research, but is years old now. The bccmd command is a default install on my RPi 4.

  • SO Q&A: Change Tx Bluetooth Linux No Effect has an answer that states that according to BT specs: only class 1 devices can change the transmitting power level by software. A quick search in an effort to learn if the RPi BT hardware is class 1 yielded nothing. However - this is worth keeping in mind if you decide to purchase a BT dongle.

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