Sunday, October 18, 2009

EMCOMMS Overview

OK, as promised, here's general overview of what I plan on covering.
This is pretty rough, and not quite finished, but I'm pretty busy moving this weekend and wanted to get something posted.
Feel free to comment or ask for additional sections, and I'll try to get something posted.

EMCOMM OVERVIEW

I. Purpose and Background
The purpose of these articles is to guide the new user, non-radio geek, into the world of maintaining communications when the normal system breaks down. I'm hoping you've provided water, food, medicine, shelter, and other items for you and your loved ones, so I'm not going to cover that.
If there's a natural disaster (Earthquake, Fire, Flood, etc) of some sort, or a man-made disaster (Riots, Terrorist Attack, Civil Breakdown, "TSHTF"), you can bet your rear-end that most 'regular' means of communications will be unavailable. The cell phone system will be overloaded, and even if you have a land-line available to you, it, too, will most likely be an unreliable means of communicating during the duration of the communications outage.
The reasons are many, but a lot of it boils down to the fact that while Ma Bell designed the system to be very robust, it was never designed for 7 million people in one area to all pick up the phone at once and dial out. In The Old Days, one of the things we were taught was that after some disaster, if you saw a pay phone with the handset dangling, please hang it back up, as an off-hook handset will request a dial tone, and enough of them off-hook would overload the system. In some cases (think 9/11 or Katrina), a major switching center might have been taken out, and all telephone and Internet communications in the affected area would be knocked out. Of course, there's always the possibility that The Government will deliberately shut things down, but I won't go there, either.

II. Scope
I'll be taking a few liberties here in an effort to make this as simple as I can, as I'm intending this for my fellow gunnies, and I'm going to assume that most of them don't have a background in communications. If you do, fine, and bear with me. If you don't, that's fine, too, and hopefully you'll at least absorb some of the basics. Most of this will cover voice communications, as that's what people are most comfortable with, and it's fairly easy to train people to use.
If you know Morse Code, and can use it, or you're an Amateur Radio operator, then these articles are probably too basic for you.
Keep in mind that NO communications system that you'll likely have available will be 100% reliable. We also won't go into secure or scrambled/encrypted communications, as if you have the gear capable of doing it, you're also far beyond the audience these articles are directed at. If you need a somewhat secure system, then work out a code with your group members ahead of time.

III. Equipment
I'm breaking the equipment down into two areas; “Wired”, and “Wireless”. I'll expand each of the areas, and give some reasons why you might want to use one over the other, depending on your requirements.

IIIb. Wired
"Wired", or "Hard Line", communications are those that rely on an actual physical connection. Whether it's a piece of copper wire between two field phones, a fiber-optic link between two computers, a hollow 'speaking tube' on a ship, or two tin cans and a piece of string, they all share the property of having an actual, physical connection from Point A to Point B. They can be very simple, to very complex. The simple systems are easy to deploy, troubleshoot, and keep running. Some don't even require a power source, although their distance is limited. Wired communications are fine for fixed station and point-to-point use.
IIIc. Wireless
“Wireless” communications are those which do not rely on an actual physical connection. Smoke signals, Semaphores, Heliographs and pocket mirrors, and even shouting at each other fall into this category, as does Radio. Since I'm a “Radio Guy”, I'll focus more on the radio aspects, as that's what I do best.

IV. Protocols for Communications
1. Analog
Analog systems are the oldest and 'simplest' systems in use. They use a signal which varies in level to represent the human voice. The louder you talk, the bigger the signal is, and the louder it sounds on the other end. The various frequencies in the voice are transmitted pretty much “As Is”, although the design of the equipment typically limits the bandwidth to about 2.7 kHz, with the frequencies from 300 Hz to 3000 Hz being sent mostly unaltered. These frequencies correspond to what's called “Communications Quality” audio, and contain the frequencies required for understandable communications. Not “HiFi” by any means, but more than adequate to do the job, and usually recognize the person talking. The original telephone system was all analog, and actually connected the pair of wires running from your telephone, to another pair of wires running to another another telephone, forming a complete “circuit”. A working system can be made with two old telephones, some wire, and a couple of batteries. Some systems are entirely 'Sound Powered', and don't even require the batteries.
2. Digital
Digital systems are much more complex, in that they take the analog signal, and convert it into a series of ones and zeroes, and then reconstruct the analog signal on the other end. This takes a lot of “stuff” to do, and is pretty hard to build from scratch. The telephone system has gone almost 100% digital in the Central Office, although the line to the subscriber is still analog. Even though you might have DSL (Digital Subscriber Line), the “bits” in the digital part of DSL are still sent using various discreet frequencies, but at much higher frequencies than voice uses.

1 comment:

Keep it civil, please....