Geometry of Bluetooth Field

[Twodogs]

TL;DR

How exacting is the Bluetooth field of a smart phone?

I am curious about an experience using earbuds with a smart phone music app. With smartphone on the porch, I was roaming the garden listening to music on a pair of earbuds. At a some distance from the smart phone the signal began to break up into a staccato of brief fragments which were just barely recognizable, but the melody was gone. Here is the question. At one point I sat down to listen and I found that in this boundary region I could get clear sound with my head in one place, but if I moved my head three inches to the right the signal broke up and I could co reliably back and forth with same result. This gave the impression that the Bluetooth wave form was much more defined than I expected, more concrete than fluid. Any thoughts on this? Thanks.

 

[Dale]

The Bluetooth signal is a radio wave. So it won’t have any features on the scale of three inches.

More likely you were hitting a signal detection or digital threshold.

Edit: I am wrong here. See below

 

[Baluncore]

This gave the impression that the Bluetooth wave form was much more defined than I expected, more concrete than fluid. Any thoughts on this? Thanks.

Bluetooth operates at about 2.4 GHz, with a wavelength of 125mm, or 5".
You can expect multipath reflections which can give some peaks and deep nulls over distances of about 2.5". Bluetooth overcomes those problems by changing frequency, jumping channels in the 2.4Ghz ISM band.
https://en.wikipedia.org/wiki/Bluetooth#Implementation

Two systems, communicating, will continuously search for a healthy signal pattern, without interference, so you will not notice jumping channels. When your headphones cannot tell the Bluetooth transmitter that they have a reception problem, the channel will not change, so as you move, you will get what is called a "picket fence" pattern in your reception. Depending on the paths and the wavelength, the pickets can be about 2.5" wide and 2.5" apart.

 

[renormalize]

Depending on the paths and the wavelength, the pickets can be about 2.5" wide and 2.5" apart.

That's also the reason that hot and cold spots on the order of that size exist inside the cavity of your microwave oven, which operates at the same frequency as Bluetooth.

 

[Dale]

Bluetooth operates at about 2.4 GHz, with a wavelength of 125mm, or 5".

oops, I should have done the math!

 

[Baluncore]

Multipath interference patterns, or standing waves, can have fine detail at quite some distance. The deep nulls are very narrow, so they are not a problem until you get near the range limit, as the OP observed.

It would be difficult, if not impossible, to form a narrow 5" beam. To do that would require an aperture significantly larger than one wavelength, which then sets the width of the beam to be greater than several wavelengths.