I don’t think it’s an impossible idea! XBEE radios in the form factor of a large watch can give you 200 kbps at 1000 ft in an indoor/urban environment, drawing 229 mA at 3.3 V. That seems to be about twice the data rate needed for clear voice communication. A 400 mAh li-ion battery is about 1x1.5 inch, so in the right ballpark. Add a 1⁄4 watt for a mini speaker and you’d get you about 25 minutes of talk time, and if you halved the data rate, you’d get 1500 ft of range. It would be pretty unwieldy and probably not quite the performance you’d hope for if you tried to hack it together from hobbyist parts, but a proper manufacturer just might be able to make it work.
The only part I’m not too sure about is antenna design. The 970 MHz XBEEs are usually run with bulky duck antennas, which wouldn’t work in a watch form factor. There are definitely designs out there for embedding antennas in wrist straps, but I don’t know much about what kind of pattern you’d get.
Hmm I think you’re right that digital voice protocols aren’t allowed on in 462-467 MHz FRS band. But there are a couple regions of the 900-1000 MHz portion of the spectrum that are allocated to commercial two-way radio, which allows digital and might be usable for this application if you were trying to actually manufacture and sell this kind of product.
If one were trying to do this as a homebrew project, either the 902-928 MHz ISM band used by the XBEEs or the 420-450 MHz band used for ham radio could work (with a ham radio license).
I don’t think it’s an impossible idea! XBEE radios in the form factor of a large watch can give you 200 kbps at 1000 ft in an indoor/urban environment, drawing 229 mA at 3.3 V. That seems to be about twice the data rate needed for clear voice communication. A 400 mAh li-ion battery is about 1x1.5 inch, so in the right ballpark. Add a 1⁄4 watt for a mini speaker and you’d get you about 25 minutes of talk time, and if you halved the data rate, you’d get 1500 ft of range. It would be pretty unwieldy and probably not quite the performance you’d hope for if you tried to hack it together from hobbyist parts, but a proper manufacturer just might be able to make it work.
The only part I’m not too sure about is antenna design. The 970 MHz XBEEs are usually run with bulky duck antennas, which wouldn’t work in a watch form factor. There are definitely designs out there for embedding antennas in wrist straps, but I don’t know much about what kind of pattern you’d get.
I don’t think digital is allowed? For example, these walkie-talkies use FRS which is FM
Hmm I think you’re right that digital voice protocols aren’t allowed on in 462-467 MHz FRS band. But there are a couple regions of the 900-1000 MHz portion of the spectrum that are allocated to commercial two-way radio, which allows digital and might be usable for this application if you were trying to actually manufacture and sell this kind of product.
If one were trying to do this as a homebrew project, either the 902-928 MHz ISM band used by the XBEEs or the 420-450 MHz band used for ham radio could work (with a ham radio license).
I think at that point you might as well use a cell phone watch?