When SHTF, we may have to rely on radio communication to stay in contact. This is part 1 of our 2 part series on emergency communication with radios.
Radio Communication: Part 1 | Staying in Contact When SHTF
Communication can be of great importance in an emergency situation. And there are many means of communication. Face to face, people can talk; further apart, light or sound can communicate information. But what if line of sight or range of sound is not available?
What we are looking for is a way to communicate over variable distances, through assorted terrain and various obstacles, without giving away our location or what is being discussed. Well, if you are a member of a Seal team or equivalent, you might be able to approach this; but otherwise, probably not. But it is possible and even practical to strive towards this level of communication to the degree practical for your circumstances. This is a class of communication which is known as “radio.”
Basic Radio Theory
What is “radio?” We exist in an environment which has what is known as the “electromagnetic spectrum.” Simply put, this is the range of all “radiation” which can exist. Some of it “vibrates” fairly slowly, like sound. Some of it vibrates very quickly indeed, such as visible light. Between these extremes we have radiation we can’t hear and can’t see (or smell or taste or touch), but which can have “information” imposed on it at one point and removed from it at a distant point. Voila, communication, and in many cases, radio communication. Note to the technically minded: there are radiations lower than sound and higher than light, but generally those are rather more difficult to use for communication.
A “vibration” is something moving back and forth between limits. This can be represented by a “waveform.” Here is the waveform for a “sine” wave, the purest wave:
The vertical axis (up and down) is “amplitude”, an indication of strength or power. The horizontal axis (left and right) is time. Trace the waveform above, starting at a point where the amplitude is “zero” (intersects the horizontal axis of the graph) and continue until you reach zero again for the second time, having gone completely up and completely down. This is known as a “cycle.” The shorter the distance on the graph (time) between the start and end of a cycle, the higher the “frequency” of the wave. Frequency describes the speed of vibration, and is usually measured as “cycles per second.” Generally this is called “Hertz,” abbreviated as “Hz”.
Many people can hear sound in the range of 20 Hz to 20,000 Hz (20 KHz). Usually we use abbreviations for powers of 1,000 for convenience: Kilo (K) indicates 1,000 of something, Mega (M) indicates 1,000,000, Giga (G) indicates 1,000,000,000, and Tera (T) indicates 1,000,000,000,000. As an aside, visible light is in the 300 THz frequency range.
Am Radio vs. FM Radio
Radio transmission is realized by taking an appropriate vibration and “modulating” it with the information to be transmitted. A radio receiver isolates the specific frequency and “demodulates” the information from the waveform. AM (amplitude modulation) and FM (frequency modulation) are two of the more common modulation methods. AM works by varying the amplitude (the up and down axis) of the waveform with the information to be transmitted. FM is performed by varying the frequency (the left and right axis) higher and lower than the specified “base” frequency.
Wavelength and Antenna Selection
Each frequency has a “wavelength,” or the physical length that one cycle takes up. This is an INVERSE relationship; as the frequency gets higher, the wavelength gets shorter. And the relationship between these two aspects is the speed of light. So, if you have an audible tone of 10 KHz, the wavelength is found by:
Wavelength = speed of light in meters per second / frequency in cycles per second = c / 10,000 = approximately 30,000 meters per cycle
Why do we care about wavelength? Well, remember, we want to strip off (demodulate) the information imposed on our waveform, and the way to do this starts with an “antenna.” This is just a structure of metal which is “tuned” to our frequency of interest. To tune to a specific frequency, we want the effective length of the antenna to be exactly a useful fraction of the wavelength. Just sitting there, the antenna “sees” its tuned frequency better than any other. Of course, most radios have a range of frequencies, so generally we tune the antenna to the middle of the range. By adding additional elements to the antenna, we can even cover multiple bands with a reasonable degree of effectiveness.
What is a “useful” fraction of wavelength? Well, best is exactly one wavelength long (known as a “full wavelength” antenna). This can be a challenge to build for low frequencies which can be kilometers long. It is much easier for high frequencies, which may only be a few inches long. If a full wavelength antenna is not practical, then go for a half, quarter, eighth or sixteenth wavelength.
Effectiveness of radio communication depends on the efficiency and height of the antennas, the power used for transmission, the “discrimination ability” of the receiver, the noise rejection capability of the modulation technique, and the intrinsic properties of the frequency used. As anyone who has listened to both AM and FM broadcast radio knows, FM is much less “noisy” than AM. Many of the bands above use FM.
Equipment for the bands above is available in Handheld (usually not 10m), Mobile and Base configurations. Handheld “walkie-talkies” are the most convenient, portable and often economical, but, they usually have marginal antennas, are located low to the ground and are limited in power. As such, they seldom give the range which the band is capable of providing, although usually better antennas can help some. Base stations tend to be fixed, and with a big, high antennas, are usually pretty visible and dependent on power. Mobile (vehicular) stations tend to be a compromise between these extremes, using the 12v power of the vehicle and an improved antenna attached to the vehicle to out perform handhelds without some of the negatives of a base station.
You could get a radio designed for one band only, and that is often the case with the non-amateur bands. “Ham” (amateur) radios are often dual band (6m and 70cm) and occasionally tri-band (adding 6m, 1.25m or 23cm) and even quad band (often including 10m). An interesting concept, which appears to not be available yet, is the Anytone TERMN-8R (“Terminator”), which has the 2m and 70cm bands, as well as Business, GMRS and MURS. With a price claimed to be under $140, this could be a superior choice for survival … if it ever becomes readily available. Allegedly, the FCC won’t or has yet to certify parts of it; every time I contact the company, they say real soon, maybe as early as tomorrow. Many months of tomorrows have gone by so far…
As you might expect, there are some premier companies producing “ham” radios – Alinco, ICOM, Yaesu and Kenwood come to mind. Of course, these fine radios have equally premier prices. BaoFeng seems to have some decent equipment at affordable prices. In the non-amateur bands, there are many choices, including Motorola and Cobra. If a radio ever claims a range, be aware that it is almost certainly completely misleading – that range can only be achieved under PERFECT conditions. I've got radios “rated” for “35 miles” which have a PRACTICAL range of a mile or two.
We have mentioned some of the types of radios which may be available for your use. Click here for part 2.
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