Hello, Frank here.
In the last post, I gave you a lot of information, websites to go to, places to get free test data and sites that you can pay for. I know a man that came to one ham radio class. He wanted to get his technician's license and he had some questions. He got his questions answered, never came back and passed the technician test a week later. He used the No Nonsense Study Guide, Technician Class that I gave you in the last post.
In that technician's guide on pages 6 & 7 it starts dealing with Ohm's Law. People that have a fear of formulas and math, lots of times will quit right here. There are only two formulas used for the technician's license. The first one is in the picture triangle, which is V over I times R. The V means voltage, the I means current or amps, and the R equals resistance. In the electronic world, we are going to substitute the letter E for the letter V. Therefore, E equals voltage in place of V equals voltage. So in your mind, or on a piece of paper, draw it out and substitute an E for the V. Now you have E over I times R.
Look at that triangle again. If you are looking for voltage and you have current, which is I, and resistance which is R, put your finger over the V, which is an unknown and you have I x R = V.
Or in the electronic world I x R = E and E = voltage. Let's say you have a given of voltage and current and you are looking for resistance. Put your finger over the R, which means resistance. Now I am going to drop the letter V from our discussion and call it E. Now you have the E on top and the I underneath which means you divide E by I, which equals R. This is how this triangle works.
I mentioned there are only two formulas. The first one is E = I x R and you have the triangle to look at. The next formula is P = E x I. A new symbol - P which equals power or wattage or watts. So, power equals current
times E or voltage. This is the formula that you will use the most. Make a triangle, put the P on top and the I and E on bottom, and you can use the same technique to find the unknown. In most of the ham radio world the E will always be 12 volts or 13.8 volts. Those two numbers are interchangeable. The reason is, your car has a 12 volt system. But, when you are driving down the road, it is actually producing 13.8 volts. When you buy a power supply to put in your house, it will convert 110 volts AC to 12 volts DC. But in reality, it will be about 13.8 volts.
Now, a little exercise here. Your power supply is putting out 13.8 volts and you have a 30 amp power supply. How much wattage or power will it produce? You cover up the P on the triangle. You have I x E. I is 30 amps. E is 13.8 volts. You take those two numbers
and multiply them. You should get 414 watts. So that means if you have a 30 amp power supply at 13.8 volts it will easily push a 100 watt radio. Easily. Here is where I like to use the 80% rule. Never use 100% of any piece of equipment. So 80% of 414 is 331 watts. Okay, let's go back to our 3rd and 4th grade math. Anytime you hear the word of, it means multiply. The 80% rule is actually 0.80. Drop the percent sign and move the decimal two places to the left. Now you have 0.80. Okee-dokee? I know I could hear all of you say 'Okee-dokee'.
These are the only two formulas you will use for math to get your technician license. E = I x R and P = E x I. Draw a little triangle with a T in it. Put the formula in there with the E on top, with I and R on the bottom.
Draw another triangle with a T in it. Put a P on top and an E and I on the bottom. You don't really have to draw the triangle, just put a big T with one letter on top and the other two letters on the bottom. Learn how to use these formulas, they will come in handy all through life. I have taught kids for years to use what I call the 'T formula'.
Now, these two formulas will give you the answer to any mathematical question on the technician exam. Sometimes you have to use one or the other to find an unknown so you can apply that unknown to the other formula. It's not tricky, maybe unknown to you at this time, but once you do this a handful of times, it's really pretty easy. And, yes, on the test, you can use a calculator. A basic four function calculator.
When I took my technician test, I asked for a piece of scratch paper. And once we all started, I wrote these formulas on the top of my piece of scratch paper. I also put other things on that piece of paper, that we will discuss later. Primarily having to do with decibels. Remember, as long as you start with a blank sheet of paper. That's your piece of scratch paper. You can put anything on there you want. But again, the only two mathematical formulas that you will use are the two we have just discussed. E = I x R and P = E x I. Also remember, V or E = voltage. I = current or amperage. R = resistance. P = power or wattage.
The man I mentioned earlier that came in and had questions he needed answers to? He walked out with the two formulas and a week later, he passed the test. The No Nonsense Technician Guide is a great way to study for the technician's test. And if you want a place to take free practice tests, I would recommend QRZ.com. Remember that you can use a four function calculator. No computers. No cell phones. But if you can push the multiply button and the divide button, then take the given information and you will have the answer.
Next time, we'll talk about what milliamps and kilowatts are and what they mean. Don't worry about the math. One other thing. Always think safety. This is a great hobby, but you don't want to fry anybody's brain. And it may be more than a great hobby when the electricity goes off and stays off. Just food for thought. So. Think safety. If you don't know what you are doing, don't do it.
Now, go get a piece of paper and draw two triangles, put a T inside each one. Put an E on top, an I and R on the bottom in the first triangle. In the second one, put a P on top and an E and I on the bottom. Get a pencil with an eraser, a four function calculator and practice some of these questions on pages 6 & 7 of the No Nonsense Technician's Guide. If you find yourself whining, then quit whining. Go in the bathroom, look in the mirror and remind yourself that God has a sense of humor.
We'll talk more later. 73, Frank