The Road Home

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Saturday, October 19, 2013

Radio - Become a Ham, Part 6

Hello, Frank here.

Sorry for the delay, it's just been real, real busy lately. My wife tells me that radio people just don't comment much, that if I was writing about green beans or cheese I would get more comments. But I see according to the stats page that hundreds of people are at least looking at these radio posts daily, so here goes.

This is a long chapter, so I am going to cut it into two pieces. And since my typist is a little bit ill today, it's going to be a little bit shorter unit. 

Radio and electromagnetic properties. Okay, this is on page 15 of the No-Nonsense Technician Class, Study Guide. Most of this stuff you can read and figure out for yourself, but I'm going to throw in some highlights. What we are going to be talking about here is radio waves. Like it says, it's an electromagnetic wave, therefore, dealing with electric and magnetic fields. 

The next term is frequency. Every radio signal, TV signal and cell phone signal all have a certain frequency and travel through space on radio waves. We talked earlier about alternating current, AC, which is also called
a sine wave. One up, then down, then back to the middle, is called a Hertz and it is measured in seconds. Another name sometimes used for the name Hertz is cycle. Your house current, for example, in the USA is 60 cycles per second, or 60 Hertz per second. When you tune in your favorite AM radio station, let's pick 1320 kilohertz. What you have is 1320 kilohertz, and remember kilo means 1000, so you have 1,320,000 Hertz per second. I know that sounds like a big number, but it's really not, especially when you get into the higher frequencies. All frequencies in the ham radio spectrum are higher than what was just mentioned. So, picture in your mind a Hertz is one wave length. That means there are 1,320,000 wave lengths per second.

Radio waves travel at the speed of light, which I was taught is 186,000 miles per second, or 300,000,000 meters per second. Remember, the reason we use meters is because radio's practical use was developed in Europe, and in Europe they use the metric system. 

Okay, this next part is going to be a little bit awkward to explain, follow along with me. As your wave length gets shorter, the frequency increases. Picture in your mind, you have 5 wavelengths  in one second, now we're dealing with time here. Now picture 10 wavelengths in one second. You notice that the wavelengths are a little more compacted, therefore, that wavelength is shorter as the frequency increases. If you want to figure out a frequency, use the 'T' formula I taught before. Put 300 on top, put meters and frequency in megahertz (MHz) on bottom. A commonly used frequency for
Technician operators is 144-148 MHz. This is commonly called the 2 meter ham band. Take 300 divided by 2 and you get 150 and that is your MHz. Okay? Now, this is not a scientific formula that is exact or precise, but it will get you in the ballpark. Another example is the 10 meter band. You want to know what the estimated frequencies are? 300 divided by 10 equals 30, or in this case 30 MHz. For the Technician, this is the only part of the HF band that a Technician can use. It's from 28.3 - 28.5 MHz. I hope you get the idea here.

RF is something that you will see often. All it means is radio frequency. But if you've read some of the other posts when I talked about frying your little girl's brain, RF is one thing that can damage you and others, so know what you are doing. An example, one day I asked my wife to hold an antenna while I was testing a radio. Not high power, nothing special, but the antenna burned her hand, just like it would if she had put her hand on an electric stove. Not a good day.

Next we are going to skim some frequency ranges. For the vast majority of ham radio operators, there are three sub-ranges of frequencies that most of us use. Yes, there are some guys beaming signals off of meteors and playing with much higher frequencies, but the average ham operator uses the three following frequency groups. HF, VHF, UHF. 

HF, which means high frequency, covers from 3 to 30 MHz. VHF, which means very high frequency, covers from 30 to 300 MHz. The UHF spectrum, ultra high frequency, covers from 300 to 3000 MHz. For Technician purposes, you'll be concerned about VHF and UHF primarily. Okay, some general information here. Most police departments, fire departments, ambulance, marine band and many other groups are covered under VHF as well
as 2 meter ham band, which is again 144-148 MHz. Most shortwave radio broadcasts are also in the HF spectrum between 3 and 30 MHz. So if you buy an HF radio, you can also listen to shortwave frequencies. And while you're looking at it, there are some radios that cover all three of these spectrum's in one radio. So if you have limited space and you want one radio that covers all, look around on some of the retail sites that I have given you. Lots of people like this type of option. Also remember, VHF and UHF are line-of-sight communications. This isn't always the case, but it is the vast majority of the time. 

Many VHF operators use what is called a repeater. Somewhere in the area, maybe on the tallest hill or a tall building, a person or group will set up a repeater. It takes the UHF or VHF signal and rebroadcasts it back
out. So, if you can hit a repeater, you can cover a much greater distance, but you still need to be within line-of-sight of the repeater. Most moderate sized towns and up, have some type of repeater around. Your local ARRL club can provide this information. 

As for HF, this is what most people envision when they think of talking around the world. There is a small piece of HF open to Technicians. That is 28.3 to 28.5 MHz, which is the 10 meter band. 

Okay, now let's put a little bit of this together. 2 meter, or 144-148 MHz, is VHF. Okay, let's see. 2 meters is a little over 6 feet. That's how big your
antenna needs to be for a full wave signal. A half-wave signal is about 3 feet. A quarter wave is about 18 inches and an eighth wave is approximately 9 inches. That's how antenna length is figured. It's a whole lot easier to put a one-half wave 2 meter antenna on your car, which is approximately 3 feet long, as compared to a 10 meter antenna which full-wave is, give or take, 30-something feet. Half-wave is approximately 17 feet. Which one is easier to operate with? A 3 foot antenna or a 17 foot antenna?

Okay, start putting some of these things together in your head. It's a whole lot better to be able to see it and understand it than to just be able to match a question with an answer. Give it time, it will soak in. And if it doesn't soak in, just memorize the answer.

That's all for today. Read back through the previous posts. Read the CB posts too, because CB is just 11 meters. Read ahead in the manual, take the practice tests, talk to your local ARRL group and best of luck. Never substitute safety. Don't drink and drive, all guns are loaded, don't ask your wife to hold an antenna, don't fry your cute little girl's brain, always practice safety. Always safety first.

We'll talk more later. 73, Frank

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