Comments on: The Radio Spectrum

By: Piper Patron

Piper Patron — Wed, 11 May 2011 05:05:08 +0000

Someone is using my brain’s and body radio signal to torture me. Is there some way to capture and trace by the originating signal and prosecute the criminals involved?

Is this how doctors generate revenue? They can pump up my blood pressure and make my chest feel so heavy like an artificial heart attack or stroke. I think they have a blue-man diagram of my body on their computer screens somewhere and are able to restrict blood flow from specific points in my brain.

Please help?

By: dogregor

dogregor — Wed, 30 Mar 2011 03:23:17 +0000

Um. It is indeed a gorgeous chart. However, it unfortunately it does not come close to showing “how the spectrum is currently allocated.” If you’ll zoom in on the lower left corner, … what’s that? Oh. Copyright 2003.

Things change. It was good then. Now, not so much.

By: rfguy

rfguy — Tue, 29 Mar 2011 21:44:55 +0000

This is great! I design little collections of electrons (and protons and neutrons, of course) to detect the jiggling at certain frequencies: see here for example. I'm also a ham radio operator (but I have a few kosher radios around too). I like the zoom in at the 24GHz area, as that's the upper limit of my equipment - I'd like to play around with electrons jiggling at 250GHz, but I can't afford it... -mark.

By: anne

anne — Mon, 28 Mar 2011 21:31:39 +0000

Responding to Emily, I seriously doubt that there are more than a few people with detailed knowledge of U.S. spectrum allocation. I expect that most of us with any level of expertise tend to be limited to our own narrow realm. Based on my experience, I can tell you a great deal about FM, including surrounding bands (VHF ‘low’ and aviation, mostly), but not much about anything else, except as it’s occasionally related to FM. For example, about 20 years ago, when digital audio broadcasting (DAB) was first proposed, many of us lobbied heavily to adopt the practice of most other countries, to use the L-bands. I swear, at one time I knew where in the spectrum the L-bands were, but I honestly don’t know now; I’d have to look it up. (I did. It’s 1452–1492 MHz.)

By: Anne

Anne — Sun, 27 Mar 2011 18:48:19 +0000

Those spaces left for radio astronomy are less useful than one might hope. They left a little hunk around various important spectral lines, which is nice if you want to do spectral-line work, but the rest of us radio astronomers are now going for fractional bandwidths of 50% and higher – when our input signal is everything from 1100-1900 MHz, there’s no way we can count on having spectrum allocated. We just have to hope there’s not too much crud and that we can distinguish it from what we want to see.

The real appeal of the far side of the Moon (or the near, for that matter) is not so much the radio silence as the low end of the spectrum – below about 20 MHz, signals don’t make it through the ionosphere. Our only idea of what’s out there at those frequencies comes from one short-lived satellite experiment, with a necessarily very small collecting area (and no directionality). There’s a lower frequency limit set by the interplanetary medium, but there’s still a lot of unexplored spectrum down there.

By: Charon

Charon — Sat, 26 Mar 2011 18:06:00 +0000

And this is why radio astronomers want telescopes on the far side of the Moon. The one damn place left that’s actually radio quiet! (As long as you can deal with the Sun and the Galaxy, but those are much more minor problems.)

By: Low Math, Meekly Interacting

Low Math, Meekly Interacting — Sat, 26 Mar 2011 15:53:20 +0000

Sure, but analog communication isn’t compressed at all, right? I think I read someplace you can fit the entire hi-def digital bandwidth of basic cable in the amount of spectrum one analog channel takes up, or at least something along those impressive lines. I would naively think even the most conservative lossless compression of digital signal would yield considerable improvements in EM real estate over any analog signal.

By: RandomGuy

RandomGuy — Fri, 25 Mar 2011 20:06:33 +0000

@Low Math: how lossy would the compressed stream be? Over a noisy medium like radio, less-than-maximal compression is used for error correction.

By: Low Math, Meekly Interacting

Low Math, Meekly Interacting — Fri, 25 Mar 2011 16:10:36 +0000

It’s amazing how crammed parts of it look, even over stretches of a whole log.

I wonder: How much wireless data transmitted these days is compressed? How much of the available spectrum could be opened up if everything were compressed?

By: Joe

Joe — Fri, 25 Mar 2011 12:28:11 +0000

@ Roderick
Not by the astronomers that I know…

By: Roderick

Roderick — Fri, 25 Mar 2011 10:38:27 +0000

@Joe

Technically particle radiation, but generally still included in the EM spectrum.

By: Joe

Joe — Fri, 25 Mar 2011 10:34:45 +0000

Errr…. Since when exactly are COSMIC RAYS an EM wave? (See the overview of the EM spectrum at the bottom.)

By: Claire C Smith

Claire C Smith — Fri, 25 Mar 2011 09:18:38 +0000

Thanks Sean….. but you’ve just broken my neck(second diagram!!!)

By: Emily

Emily — Fri, 25 Mar 2011 01:17:59 +0000

I wonder what the high score would be for the question: how much of this chart could an individual expert reproduce from memory? Presumably there are allocation experts who really know this stuff, but it certainly looks daunting when it is presented like this.

By: teawithbuzz

teawithbuzz — Thu, 24 Mar 2011 23:59:36 +0000

I have a big poster of this, that I drag out and share with my high school students when we get to the electromagnetic spectrum. It is nice to have it all big enough to read and also still see it all at once!

By: Matt B.

Matt B. — Thu, 24 Mar 2011 22:19:56 +0000

Nice! They got the colour of magic in there. Thanks, Supernova.

By: Supernova

Supernova — Thu, 24 Mar 2011 18:26:50 +0000

Someone has to post this, so I will: http://xkcd.com/273/

By: joe

joe — Thu, 24 Mar 2011 17:34:52 +0000

SETI has found alien life! Oh wait, that’s just AT&T encroaching on scientific frequencies.