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Comment by danielmittleman | Hacker News Reader

Light IS an electromagnetic wave, so to say it has similar properties to EM waves is kind of like saying that pizza has similar properties to food.

Also not sure what you mean by "needs a vacuum to make it possible" seeing as we generate terahertz radiation in air all the time, using a variety of techniques that use off-the-shelf commercial products.

As far as I can tell, the article doesn't say very much that is outright false, although for sure he glosses over some fairly complex concepts with very little detail in a few cases. His statement about "a few dozen meters" of propagation range is outright false, but other than that he more or less got the facts right.

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Touche, you're right. I should've worded that differently in the moment.

I was trying to come from the perspective of the author, where he tries to argue about difference of appliances through technological means. E.g. using a laser for communication vs using a wifi like transmitter setup.

Both are EM waves but the practicality of the environment with degradation and radiation and the medium that are common for us (gases in the air) make the approach of how to reach the target vibration (in the sense of targeting a specific antenna length on a specific wavelength) harder when trying to use the sub infrared spectrum.

As I wanted to say, I think finding the right material and medium will be a huge challenge in this regard.

Well, actually it's much easier at lower frequencies. After all, your cell phone operates at around 2.5 GHz (if it is a 4G phone).

But yes, there are huge challenges involved in using higher frequencies for communications. We will eventually use 120 GHz, and then probably 290 GHz, for comms, but it will be a while. The technical challenges are... not trivial.

You might be interested to know that the Japanese television broadcasts of the 2008 Olympic games in Beijing made use of a wireless link operating at 120 GHz. It was really just a demonstration of feasibility, not a fully deployed system. But still, pretty fantastic. And that was 14 years ago...

From what I heard at ESA projects (not being directly involved) the L-band seems to be able to penetrate clouds and static charges in the atmosphere, whereas higher frequencies like the Ku-Band (12-18Ghz) tend to collide too much with rainy clouds and droplets in the air.

That's why I was assuming that higher frequencies than the Ku Band will likely lead to more signal degradation on the way.

I also don't have any calculations or plots in my head for the minima and maxima, so I could be totally wrong about this :D

120Ghz is quite amazing as an achievement though. They probably used a wider band and multiple channels, I would assume?

edit: looked up a little on K (18-27Ghz) and Ka band (26.5-40Ghz), but both seem to be still unfeasible for long range communications.

> looked up a little on K (18-27Ghz) and Ka band (26.5-40Ghz), but both seem to be still unfeasible for long range communications

umm, Ka band is rather popular for satellite communications (very long range by most standards!). Yes things like L band are great for propagation and penetration, but the fundamental motivation for going to higher frequencies is that they can carry more data. This is the same reason you don't get music on AM radio--there's not enough bandwidth for good sound quality.

The atmospheric transmission's dependence on frequency is complicated. There are water vapor resonances above 100 GHz which one would want to avoid. There is frequency-dependent scattering from droplets, and there is a continuum background from water vapor dimers that rises with frequency. It is a very non-trivial situation. Having said that... the 2008 Olympics demonstration had a broadcast range of about 1 km, and people have demonstrated ranges up to several km at higher frequencies, even close to 300 GHz. So although it will never be as good as the range one can obtain at lower frequencies, there's a lot one can do.

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