
Ask HN: Question about radio waves - ratsoman2
What frequency would be best for within 1 mile in a city or suburban area?<p>Follow up, Why are restaurant notification buzzers so limited in distance and how could they improve this.<p>thanks
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Gibbon1
There are four components that effect range. Transmit power, attenuation,
receive sensitivity, and interference.

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.

~~~
wahern
Isn't interference just another way to describe sensitivity? From the classic
Salon article, The Myth of Interference: "'Interference is a metaphor that
paints an old limitation of technology as a fact of nature.' So says David P.
Reed, electrical engineer, computer scientist, and one of the architects of
the Internet."
[https://www.salon.com/2003/03/12/spectrum/](https://www.salon.com/2003/03/12/spectrum/)

~~~
Gibbon1
Any receiver design, bandwidth and modulation technology will have an ultimate
sensitivity. Far as I understand this is due to both noise created by the
circuit itself and the thermal noise over the band.

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.

