Think of a plus sign: + . That's what an EM wave looks like when you look down the length of it. One section is alternating up and down (positive and negative) and the other left and right (positive and negative). Wikipedia has a good illustration and explanation

An easy way to remember is to recall a plus sign. It's all right angles, so are the parts of the wave!

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There's always an electric and magnetic field to a radio wave, and they're oriented 90 degrees to each other. You could use either magnetic or electric to define polarization, but it's conventional to use the electric field (not the magnetic field, or a ratio).

Polarization has nothing to do with the velocity of a radio wave, hence the ratio of velocity to wavelength has nothing to do with polarization.

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Tags: arrl chapter 4 arrl module 8

Radio waves are also sometimes referred to as electromagnetic waves because they are made up of both electric and magnetic fields.

For this reason a capacitor (which stores energy in an electric field) and an inductor (which stores energy in a magnetic field) can both be used to help tune an antenna. Some antennas incorporate one or both as part of the design and antenna tuners utilize variable capacitors and inductors to function.

AC and DC are different types of current and have little or nothing to do with radio waves; Voltage and current are components of power and may be used to produce radio waves but do not comprise them.

Ionizing and non-ionizing radiation is probably the most confusing distractor but don't fall for it - that's not it either =]

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Tags: definitions radio waves arrl chapter 4 arrl module 8

All electric, magnetic, and electromagnetic waves travel at the same speed. This includes light waves, radio waves, electrical waves, and magnetic waves.

Sound waves are a different story.

Just remember that radio waves and light waves are actually not all that different when it comes down to it; they're just a different frequency. They travel at the same speed.

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Tags: radio waves arrl chapter 2 arrl module 2

The shorter the wavelength, the higher the frequency. Hence, frequency and wavelength are inversely proportional to each other. Wavelength measures the distance between each peak. Higher the frequency, the more peaks there are. Frequency measures the amount of peaks.

To visualize this, think about how you would graph a wave (radio waves are graphed as sine waves). The distance left to right represents time, and the distance from one peak of the wave to the next is the wavelength and each time you reach the peak again is one cycle. The frequency is the number of cycles per second; thus, if you have more cycles in the same distance (higher frequency), the distance between peaks (wavelength) will be shorter.

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Tags: radio waves frequencies arrl chapter 2 arrl module 2

Wavelength in meters equals 300 divided by frequency in megahertz.

\begin{align} \lambda _\text{ (meters)} = \frac{300}{f_\text{ (MHz)}} \end{align}

Knowing this will help you with quite a few of the problems in the Technician class question pool!

For example, if you see the frequency \(150\text{ MHz}\) and need to know what band it is in, divide the speed of light by the frequency. MHz cancels out, which leaves you with \(\frac{300}{150\text{ MHz}} = 2\text{ meters}\)!

The \(150\text{ MHz}\) frequency is exactly in the middle of the 2-meter band. If your number is not quite on (e.g. \(\frac{300}{144\text{ MHz}} = 2.08\text{ meters}\)) that's okay, because the bands have a little play both above and below the "wavelength" number.

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More Detail

Ever wonder where the value \(300\) comes from?

Here's the general form of the equation above:

\[\lambda \times f = c\]

The units are all basic SI units (International System of Units or Metric System) -- let's add them for clarity:

\[\lambda_\text{ (meters)} \times f_\text{ (Hz)} = c_\text{ (meters per second)}\]

The speed of light \(c\) is a constant, so we can plug that value in: \begin{align} \lambda_\text{ (meters)} \times f_\text{ (Hz)} &= 3.00 \times 10^8\text{ m/s} \end{align}

There are \(10^6\text{ Hz}\) in each \(\text{MHz}\), so let's divide both sides by \(10^6\) and simplify: \begin{align} \frac{\lambda_\text{ (meters)} \times f_\text{ (Hz)}}{10^6} &= \frac{3.00 \times 10^8\text{ m/s}}{10^6}\\ \lambda_\text{ (meters)} \times \frac{f_\text{ (Hz)}}{10^6} &= 3.00 \times 10^2\text{ m/s}\\ \lambda_\text{ (meters)} \times f_\text{ (MHz)} &= 300 \text{ m/s}\\ \lambda_\text{ (meters)} &= \frac{ 300 \text{ m/s} }{ f_\text{ (MHz)}}\\ \end{align}

Easy memory tip - The number "300" appears in the middle of the correct answer.

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Tags: math radio waves frequencies formulas arrl chapter 2 arrl module 2

This is a common part of Ham vocabulary. You'll hear something like: "I was talking on the 2-meter band last night..", which actually means they were talking somewhere between 144Mhz and 148Mhz (the authorized frequencies with a 2-meter wavelength). Other common terms are 33cm (the 902Mhz band), 70cm (the 440Mhz band), etc. Each frequency range has a corresponding wave-length that hams will refer to.

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Tags: radio waves frequencies arrl chapter 2 arrl module 2

One thing that often confuses new hams is that the terms "HF", "VHF', and "UHF" actually refer to different parts of the spectrum, with "HF" or "High Frequency" actually referring to frequencies that are the lowest commonly used by Amateur Radio Operators.

The range are thus:

• HF (High Frequency) is from 3MHz to 30MHz
• VHF (Very High Frequency) is from 30MHz to 300MHz (and includes the popular 2M band at 144-148MHz)
• UHF (Ultra High Frequency) is from 300MHz to 3000Mhz

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Tags: frequencies memorizing vhf arrl chapter 2 arrl module 2

One thing that often confuses new hams is that the terms "HF," "VHF," and "UHF" actually refer to different parts of the spectrum, with "HF" or "High Frequency" actually referring to frequencies that are the lowest commonly used by Amateur Radio Operators.

The ranges are thus:

• HF (High Frequency) is from 3MHz to 30MHz
• VHF (Very High Frequency) is from 30MHz to 300MHz (and includes the popular 2M band at 144-148MHz)
• UHF (Ultra High Frequency) is from 300MHz to 3000MHz Do not get confused by the kHz option; it is in MHz, not kHz

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Tags: frequencies memorizing uhf arrl chapter 2 arrl module 2

One thing that often confuses new hams is that the terms "HF," "VHF," and "UHF" actually refer to different parts of the spectrum, with "HF" or "High Frequency" actually referring to frequencies that are the lowest commonly used by Amateur Radio Operators. In other words, HF frequencies may be "high frequency", but they are lower frequency than "very high frequency" and "ultra high frequency".

300 to 3000 KHz are very rarely used by hams, but that would be the "Medium Frequency" or MF band.

The ranges are thus:

• LF (Low Frequency) is from 30 kHz to 300 kHz
• MF (Medium Frequency) is from 300 kHz to 3000 kHz
• HF (High Frequency) is from 3 MHz to 30 MHz
• VHF (Very High Frequency) is from 30MHz to 300MHz (and includes the popular 2M band at 144-148MHz)
• UHF (Ultra High Frequency) is from 300MHz to 3000MHz

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Tags: frequencies memorizing hf arrl chapter 2 arrl module 2

This is a useful number to know; it is, of course, the speed of light or approximately

\begin{align} 3\times10^8 \text{m/sec} = 300,000,000\text{ m/sec} \end{align}

One really useful thing about this number is that it comes out to the same range as "Mega" (6 zeros after 300), so it can be used as a quick way to calculate wavelength in MegaHz (MHz).

For example, if you see the frequency \(150\text{ MHz}\) and need to know what band it is in, divide the speed of light by the frequency. MHz cancels out, which leaves you with \(\frac{300}{150\text{ MHz}} = 2\text{ meters}\)!

The \(150\text{ MHz}\) frequency is exactly in the middle of the 2-meter band. If your number is not quite on (e.g. \(\frac{300}{144\text{ MHz}} = 2.08\text{ meters}\)) that's okay, because the bands have a little play both above and below the "wavelength" number.

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Tags: radio waves memorizing arrl chapter 2 arrl module 2