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Comment by chrissnell | Hacker News Reader

And why not? When I lived in Utah, I could easily hit a mountain-top ham radio repeater 20+ miles away with my little 5W handheld radio. A small weather balloon with a sub-1W transmitter can easily be heard at 100K feet altitude by people hundreds of miles away. So long as you have LoS, it's not problem.

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I'm from Northern Utah and used to try to get a response from repeaters on my handheld radio. Being and introvert, that didn't really want to talk to people, it was one of the few things I really found interesting on HAM. I got pretty far but I was unable to hit the repeater in Wendover, NV (it was my next goal before I gave up). I used the local mountains to get myself up to an elevation where the curvature of the earth still allowed line of sight. I think Wendover is about 120 miles, line of sight, from the drive-able mountain top I selected. The expanse has two mountain ranges but there are some low spots that I thought I might be able to get through. The rest of it runs pretty flat over the salt flats.

Water molecules block 2.4Ghz spectrum that WiFi uses.

This is on purpose: the idea is to make the common WiFi (and Bluetooth) bands short range on purpose, so that many people within a city block can have local WiFi or local Bluetooth without interfering with each other.

So 2.4GHz over a long distance kinda goes against the design of WiFi / Bluetooth.

> Water molecules block 2.4Ghz spectrum that WiFi uses.

This isnt really true to any significant degree that matters, unless you are literally under water.

Rain fade is a thing, but is really only meaningful above 10GHz.

edit: I should note, its not that water droplets dont attenuate radio signals, its just that losses on a typical radio path are already huge in perfectly clear weather - you might lose 99.99999999% (100dB) or more of your signal strength between transmitter and receiver anyways.

The idea really was that 2.4GHz spectrum was already polluted by microwave ovens (because microwave ovens operate at the resonance frequency of water molecules), so it was left for public use.

That's a common misconception:

https://www.wtamu.edu/~cbaird/sq/2014/10/15/why-are-the-micr...

> The microwaves in a microwave oven are not tuned to a resonant frequency of water. […]

> They heat the food through simple dielectric heating. […] Many types of molecules in the food absorb energy from the microwaves in this way, and not just water molecules.

2.4Ghz was a ISM junk band long before domestic microwave ovens arrived. In fact 2.4Ghz was used for microwave ovens specifically because it was an ISM band, and therefore was available.

Almost. 2.4GHz had been set aside for consumer devices long before wifi. Microwaves are essentially very powerful unlicensed transmitters. Wifi devices are also all unlicensed transmitters. So 2.4GHz devices don't use the same space despite microwaves, they use it because that space had already been given over to unlicensed devices. If not for microwave ovens we might not have wifi as it is today.

Back when people were gobbling up the spectrum, the military didn't care about 2.4GHz because of the water absorption issues. It wasn't good for communication at long distances and so it was allowed for consumer devices.

1W at a very narrow bandwidth, is a very different thing form a 20mhz wide signal at 2.4ghz with ~71mW transmitter (100mW eirp with a dipole). Just calculate the peak power at those bandwidths.

Point taken. I didn’t consider that.

You can work the ISS voice repeater with a handheld and it is around 400km away. Line of sight is everything and more so as you increase the frequency.

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