In Bluetooth tech, which of the two decides the distance that one can get unhindered transmission, a transmitter or receiver?

Bluetooth is a form of wireless communication. In wireless connections the component responsible for establishing the physical layer (the part over which actual data exchange takes place) is the antenna.

The distance to which the signal can travel depends upon

The construction of the antenna. Its geometry,the materials it's made of. The conditions in which it operates

The placement of the antenna. Whether the signal it generates has to pass through obstacles or there is a clear line of sight.

Now the thing about antennas is that they are reciprocal. This means that If an antenna is a good transmitter (whatever parameters you choose to define good) it will also be a good receiver(on the same parameters).

But even when you use similar antennas the operating conditions of the transmitter and receiver can be different leading to a dismilliar performance between two devices.

Now coming to your question. It's not so much whether the transmitter or the receiver that decides the distance. It's about how good can they work together.

Because mobile devices (or other embedded devices like USB Bluetooth) have inbuilt antennas the distance to which they can transmit is limited.

Now if you use device to device communication so that you have two embedded antennas due to the principle of reciprocity both transmission and reception abilities are limited and hence the distance to which the link can work is small. This is why they are classified as PAN ,personal area networks.

Add to it the responsivity of the chips (how sensitive they are,more sensitivity allows them to gather faint signals and less sensitivity makes them neglect it) and you have got a combination that limits the effective range.

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