Getting Started in Ham Radio, Part 2 – Wavelengths and Watts and Whatnot
You can also read part one here. So you’ve already decided on getting an amateur radio license, and you find yourself with a few questions. One of the first questions you have is probably, “What is all this ‘wavelength’ and ‘meter band’ and ‘HF’ stuff?” Or, maybe you wonder what that guy was talking about when he invited you to “check in to our prepper net down on 80, we’re at 3850.” Like most pursuits, ham radio uses some specialized jargon. Let’s try to clear up a few of the basics. 
“What is all this crap?” SURFING THE WAVELENGTHS Ham radio operates on certain segments of radio frequencies, or bands. Just like AM radio is found between 540 and 1710 kHz, and FM radio is found between 87 and 108 MHz, ham radio has its own sections of bandwidth to occupy. These bands are generally referred to using the approximate physical wavelength of the radio waves. For instance, the “80-meter band” runs from 3.500 MHz to 4.000 MHz (3500 to 4000 kHz), as 80 meters is the approximate physical wavelength of a radio wave at those frequencies. Likewise, anything from 28.000 MHz to 29.700 MHz is considered the “10-meter band,” and so on. Remember, these are approximations, as wavelengths change with every change in frequency. The “band plan” designations just make it easier to group them together. If you know the frequency and want to calculate the approximate wavelength, there’s an easy formula to get a fast-and-dirty result. Just take 300 divided by the frequency in MHz. For example, using this formula with 146.5 MHz, we come up with a result of 300/146.5 = 2.047. Correspondingly, 146.5 MHz is found in the 2-meter band. Another one, 14.150 MHz, would be 300/14.150 = 21.20. That means that 14.150 falls in the 20-meter band. Frequencies in ham radio are referred to in either megahertz (MHz) or kilohertz (kHz). 1000 kHz = 1 MHz. You might hear somebody referring to a contact they made on 40 meters at either “seven point two” or at “seventy-two hundred.” That’s just two ways of saying the same thing. 7.2 MHz = 7200 kHz. Using our previous formula, 300/7.2 = 41.66, so that frequency is in the 40 meter band. So, when that guy earlier asked you to join a discussion net “down on 80 at 3850,” you now know that if you tune in to 3.850 MHz on the 80-meter band, that’s where you’ll find him. Pretty easy! 
“Basic list of frequencies” WHAT’S THE FREQUENCY, KENNETH? For those of you who are old enough, do you remember your old TV set that had separate dials for VHF and UHF? Those terms stand for Very High Frequency and Ultra High Frequency, and while your TV shows now come via cable or satellite, VHF and UHF, along with HF (High Frequency), are still terms you encounter every day in ham radio. Although there are frequencies both above and below, the three most common in ham radio are HF, VHF and UHF. Ham radio HF starts at 1.8 MHz (just above AM broadcast frequencies) and goes the whole way up to 30 MHz, and includes the 160-, 80-, 60-, 40-, 30-, 20-, 17-, 15-, 12- and 10-meter bands. This is the frequency range that you’ll sometimes hear referred to as “shortwave.” Ham radio VHF starts at 50 MHz and goes up through 300 MHz, and includes the 6-, 2- and 1.25-meter bands. FM broadcast radio (87 MHz-108 MHz) falls in the middle of this segment. Ham radio UHF frequencies start at 300 MHz and run the whole way up to 3000 MHz, and you’ll find most users on the 70-cm and 33-cm bands. Great, so… what’s the difference? The short answer to that question is “distance.” The HF bands are generally more geared towards long-distance communication, while the VHF and UHF bands are for more local communication. For example, in an SHTF situation, most of your communication with the outside world would be on the HF frequencies, and for local operations the hams in your group would likely be using handheld or mobile VHF radios to communicate with each other. Those rules aren’t written in stone – you can talk to someone just a few miles away on HF, and if conditions are right you can get out pretty far on VHF, but generally, lower frequencies = longer potential communication distance. For a person holding a technician license, most of your operating will be on VHF and UHF, where you have full privileges. Technicians have some very limited voice privileges on 10-meter HF, but other than that, if you’re a Technician who wants to use HF, you’re mostly limited to morse code. But, if you have your Tech license and you’ve read this far, you’re probably already chomping at the bit to upgrade to General and then Extra Class, which will open up the whole world of HF frequencies for you! 
“Electronics formulas you need to know” POWER TO THE PEOPLE! One of the hardest thing for an aspiring ham to learn, particularly one without any electronics experience, is Ohm’s Law. While it might make your eyes glaze over just like high school algebra, it’s actually a very simple formula that you’ll need to understand whenever you’re building or troubleshooting something. It’s also required reading for taking your amateur radio test! There are many formulas that are part of Ohm’s Law, but these are the basics you’ll need to know to get started. Any beginner’s electronics text will tell you that volts are electric potential, amperes are current, ohms are resistance and watts are power, but what does that really mean? As a kid, I was taught to think of it like plumbing: Volts are the water in the pipe, amperes are the water flow, ohms are the size of the pipe and watts are how much water you get out of the spigot. Lots of water, high flow rate and a large pipe will give you a lot of water in your bucket, while less water, low flow and a small pipe will give you a lot less. Electricity works in much the same way (just don’t mix the two together!). Put more volts or current in the wire (more water or higher flow in the pipe), and you’ll get more out of the other end. Higher resistance (a smaller pipe) will let through less power than lower resistance. The chart above shows the easy way to calculate these figures. For example, let’s say you have a 12 volt power source, and you want to generate 2 amps of power. How much resistance will you need in your circuit? As the chart shows, resistance = volts / amps. 12 / 2 = 6, so you’ll need 6 ohms of resistance in your circuit. So, you’ve got your 12 volts at 2 amps, but how many watts of power is that giving you. Power = volts x amps, so 12 volts x 2 amps = 24 watts. Easy! These two basic charts will get you started with most of what you need to know in your ham radio projects. If you haven’t gotten your Technician license yet, now’s the time to get started. If you have, well, now’s the time to upgrade to General and then to Extra Class! The same resources available for Technician study are also available for General and Extra, so with a little bit of effort, you’ll have no problem at all. In my first entry we talked about licensing, and this time we went over some basics, so next time, let’s start getting some equipment together and then we can get radio active! Join thousands of preppers and get all my survival tips for FREE! Subscribe to The Survivalist Blog dot Net via RSS or via e-mail. November 23, 2012 M.D. Creekmore [send him mail] is a full-time blogger and preparedness consultant. He currently lives completely off-grid somewhere in the Appalachian mountains and is the author of 31 Days to Survival and The Dirt Cheap Survival Retreat both published by Paladin Press. To connect with M.D. Creekmore please visit his Survival Blog. Copyright © 2012 The Survivalist Blog
|
