Ask HN: Question about radio waves
What frequency would be best for within 1 mile in a city or suburban area?
Follow up, Why are restaurant notification buzzers so limited in distance and how could they improve this.
thanks
Follow up, Why are restaurant notification buzzers so limited in distance and how could they improve this.
thanks
Transmit power is easy, more power more range.
Attenuation depends on frequency in a cluttered environment. Everything being equal lower frequencies work a lot better than high ones. Contrary to what you'll hear or read radio signals in a cluttered environment doesn't follow an inverse square law in practice. It's a lot worse than that.
attenuation = const * distance ^ -k
Where k depends on frequency. For FM/AM radio (important where the tower is on a hill) k = 2.5
900MHZ k is ~3 and for 2.4GHz is ~3.5
So 900MHZ is a lot better than 2.4GHZ. 433 is likely better than either.
Receive sensitivity depends on the antenna and front end design. And modulation type and strongly on the signal bandwidth. And very importantly the presence of interfering signals. Low data rate spread spectrum will give you the highest receive sensitivity.
You can't get better than that.
Then you add interference which raises your noise floor both statically and dynamically. Unlicensed bands tend to be polluted with short coherent pulses of RF.
One issue with interference. While attenuation is symmetrical between two transceivers, interference is utterly not symmetric.