What? I Can't Hear You -- Shout Louder!

Sat, 11 Jul 2009

One of the big problems with running networks over radios (Access Points -- APs, Ad-Hoc networks) is that the folks trying to run them have a networking background and not a background in radios. And while a background in both would be good, finding radio folks who want to work networking is difficult. So most wireless service providers have networking folks and few if any radio folks.

So why is this a big deal? We're talking about network connectivity after all. Folks really need to know about networks. The radios either work or they don't. Well, that's true enough. But what happens when you have networking folks only is they know a link should work, or they think it should work better than it does.

It's at this point, folks that know little to nothing about radios have to understand a little about how they work. Imagine you and a friend are on opposite sides of a quiet room. It's not difficult to have a conversation, and no need to shout. Now imagine a few other folks start to show up. They're also conversing, some are rattling glasses, etc. It becomes a bit more difficult to carry on a conversation -- unless you raise your voices. The problem with raising your voices, is that anyone else conversing in the room will also have to raise their voices to be heard. Soon, the din is unbelievably loud.

The same thing happens with radios. The background talking is called noise. And the noise floor rises. Most networking folks response to communications under these circumstances is to slap on an amplifier and shout over everyone else. Problem is, everyone else does the same thing. The other problem is that amplifiers have a nasty habit of amplifying not only signal, but noise as well. Things only deteriorate more.

The secret is not to shout louder, but to listen better. I recently visited a children's science museum where children could experience various things. One of the exhibits was a dish that looked like a dish antenna. In fact, it also looked like a telescope mirror. Really, it could have been put into service as any number of things. All this object did was focus waves (sound, light, radio, whatever spectrum) at a point just in front of the dish. An identical dish 20 feet across the room did the same. Someone at the far dish could whisper, and the person across the room had no trouble hearing at all, despite conversations going on all around.

This is exactly what networking folks need to learn that radio folks already know: it's not how loud you shout, but how well you can hear. And choosing the correct antenna makes all the difference in the world. Now understand that parabolic antennas and grid antennas, that can hear very well, can only hear transmitters within a very narrow beamwidth in front of them. Sector antennas get slowly deafer as their aperture gets wider. By the time you get to omni-directional antennas, those antennas are deaf as the posts they look to be.

But it all comes down to choosing the right tool for the job, and knowing not only how to make the best use of it, but also understanding its limitations -- i.e., when will it just not work. Now I could go into long discussions involving the mathematics of radio communications. But it's best to just go find a good signal to noise ratio (SNR) calculator and use it. The best ones will allow you to specify the radiated power and antenna characteristics of both sides vice only one side. They will also allow you to mix and match power output (mW or db), distance (km or mi), etc. Do I know of a good one? Of course -- I wrote it for myself years ago. It's not perfect, but the calculations work correctly. See http://www.pananix.com/cgi-bin/rfcalcs.pl.

So please, no need to shout, just use the proper set of ears (antennae). You'll be surprised at the results.

David-

What? I Can't Hear You -- Shout Louder!

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