Radio Communication Methods During Emergencies- Part 1, by R. in NC

Communications Overview and General Guidelines

About This Article

A modern two-way radio combines transmit and receive components together and is known as a transceiver. In this article I will use the terms radio and transceiver interchangeably. I’m also trying to write this to the largest audience possible and for that reason I may sacrifice technical accuracy in order to express the concept.

Not all emergencies will require advanced communications equipment. Common usage technologies, such as email, voice mail, and SMS texting, should not be ignored. The more options you are able to take advantage of, the better your chances of establishing communications.

Radio Communications and Where To Start

When it comes to radios, different frequencies propagate differently and have different send and receive requirements. Some frequencies are great for your neighborhood but will rarely be usable over three miles; others can talk across your neighborhood and international but may have gaps in communicating throughout your state.

Each frequency has a “ground wave” or “line of sight” aspect where it spreads out horizontally and a “sky wave” aspect where it can bounce off of the troposphere or ionosphere, depending on conditions. These “sky wave” conditions are impacted by the sun cycle, time of day, temperature, and season. Some frequencies only bounce off the troposphere or ionosphere under unique conditions. Each frequency also has specific length requirements around the size of the antenna and the optimal height to place that antenna. This is all a balancing act between your personal requirements and technical requirements. This balancing act will require testing and tinkering.

General Rules of Distance – Buyer Beware

VHF/UHF Ham and FRS/GMRS are line of sight. This means that the curve of the earth gets in the way of the signal. The higher two antennas are the greater the distance over which they can be used for communications. When both antennas are about six feet off the ground and no object interference exists, you can expect a maximum of about six miles distance under theoretically optimal conditions and with enough power on both radios to get a signal through the background noise. Note that this isn’t always the case, and often VHF/UHF Ham radios, and sometimes GMRS, use repeaters that have antennas a hundred or more feet above the ground.

With a repeater like this, line of site is between your radio and the tower. Conversations between people 20 or 30 miles apart are also common using a repeater if it is in between them. FRS does not allow for repeaters or extended antennas, MURS allows for limited antenna deployments, and GMRS repeaters are rare.

What Line of Sight Calculations Mean

Calculating the line of sight doesn’t mean that two points can actually talk. I’m putting the basic formula below, but remember this: Just because you can draw a straight line between two points does not mean you didn’t run out of ink along the way. Don’t think of these equations in terms of how far you can talk; think of them in terms of knowing at what point it’s impossible to talk past. Personally, I have a D-Star repeater within line of sight but near the edge.

Digital, like D-star, is funny. It compresses the bandwidth, so in theory it should go further than standard FM; but that connection needs to be consistent. There’s probably a bunch of trees that cause me to drop in and out, or I just don’t have enough power to maintain a connection, because I can hardly be heard on that repeater. I can connect to different FM-only repeaters at near the same distance, without issue.

Basic Formula for Line of Sight

The basic formula to get the theoretical line of sight is:

(1.23 * square root of (height in feet of antenna 1 ) + 1.23 * square root of (height in feet of antenna 2 ) = line of sight in Nautical Miles).

General Distances of Handheld Radios

To get a general idea of how far two handheld radios can talk VHF or UHF, it would be 1.23*2.449 + 1.23*2.449 = 6.025 Nautical Miles or about 6.933 standard miles. The 1.23 is related to the radius of the earth, and there are variations in this value depending on the terrain. Personally, I replace the 1.23 with 1 in that equation. The math is faster, and range would be more realistic, for a handheld or low-power radio. For a simple way to calculate the distance when you know the height of two antennas and there are no major obstacles between them, try using this website link . Note that they do some rounding and wishful thinking.

General Distances of CB Radios

CB, 10/6 meters radios use ground wave and sometimes sky wave propagation. This means that the curve of the earth gets in the way, like with VHF/UHF, but the radio wave starts to bend with the earth. You might get less than 3.5 miles, and you might get 10 miles out of it. The physical local characteristics of earth impacts distance. There are times that temperature differences in atmospheric layers, and the number of sun spots, allow for great distances by bounding the signals back and forth between the earth and ionosphere/troposphere.

General Distances of  HF Radios

HF radios use ground wave and sometimes sky wave propagation. As you increase in wavelength and decrease in MHz of a frequency, the earth has more of an impact on the curve of the radio wave and ground wave distance increases for most bands. Unfortunately, along with this increase in distance, there is an increase in the size and height of your antenna. Keep in mind that there is also almost always a gap between where the ground wave ends and where the ionospheric bounced wave comes back to earth. This dead-zone also varies in length, depending on numerous conditions. (See Dead Zone below.)

Purchasing Communications Devices

When purchasing new electronics, look for the following features:

  • Water Proofing. Regardless of a product’s statement that it is waterproof, have alternate layers of protection. Seals fail for all kinds of reasons. Make sure you can keep your electronics dry. Note that most electronics are not waterproof, but most have an IP rating on the device. Look for the IP rating, and it will tell you impact, water, and dust resistance. See the following link for a description: .
  • Shock and Impact Resistance. Similar to waterproofing, make sure you can protect your equipment from physical damage. The IP rating of a device also covers what kind of impact a device can withstand.
  • Have a way to power and charge the device. Don’t rely on just one method of powering and charging a device. Many portable devices use a USB charger plugged into an AC wall outlet. If your device uses this, make sure to also have a cigarette lighter charger adapter (car DC adapter) for charging. Some devices can also run directly off of an automobile’s DC current. Know if yours can. If your device has a special battery, see if there are options for using common batteries in an emergency. Devices that require more amperage often run off of AC to DC converters/inverters (power supply). These devices can usually run directly off of a 12v DC battery, such as a car battery. If yours can, make sure you can charge that battery when there is a power outage. Solar panels can and often are plugged into 12v DC batteries. Quality solar chargers have diodes that prevent the battery from draining back into the solar panel when the sun goes down. This topic is beyond the scope of this article.

When integrating your electronics with others, pay attention to Bands, Frequency, and Modulation. Radios that are stronger than FRS and CB are commonly referred to by the bands they support. A Band is a range of like frequencies, represented in their general wavelength. For instance, a CB radio operates around 26MHz. To get the band, just divide 300 by 26 and you end up with 11.5, which is usually rounded down to the whole number (11 meter band). For a 144MHz radio, the band is 2 meters. Modulation can be described as the mode in which that wavelength is sent out and received; think FM vs AM on your car radio.

  • Bands are usually grouped in three types of radios: VHF/UHF, HF/50Mhz, and Specialized combination, including single band radios. A 10 Meter radio is a common single band radio.
  • When looking at getting an advanced radio, it is very important to pay attention to the Modulation that the radio supports. For an FRS radio, you have less to be concerned about because there are fewer options available to the customer. However, when looking for a HF, 6m or 10 Ham radio, there are a lot of options. AM/SSB/CW and even FM is used on 10 and 6 meter repeaters.
  • Pay attention to what is used in your area. You can go online and look up local Ham radio clubs. Often they will list local repeaters and the options those repeaters support. Knowing what is used actively in your area will help when it comes to shorter range, 70cm/2m/6m/10m repeaters along with supported digital modes such as DMR, Echolink, and DSTAR.
  • Note: There are a number of 70cm/2m/6m/10m combination radios out there. Almost all of them are FM only, and most communications on 6m/10m use AM or SSB only. In addition, the frequency range for connecting to a 10m repeater is outside of the tech license range.

Common and Non-FCC License Dependent Communications

The simplest way to set up communications between two or more people is by using non-licensed radio communications. As the title suggests, these do not require special licensing by the FCC; however, the radio technologies that do not require licenses are the ones that are limited in power and range. The greatest amount of flexibility and range around radio-based communications is covered in the FCC license dependent communications section below.

Also remember that just because you may already have a Ham radio license doesn’t mean these non-licensed devices should be ignored. Since most people will have access to them, they may actually end up being extremely useful.

Tomorrow, we’ll take a look at some of these devices.

See Also:

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  1. I’m lookin forward to this series, as comm is often overlooked in preps. In my group, we standardized with Cobra CB 29X’s, but the point of these is to work towards establishing initial linkup during the first stages of an event. We all love within 15 miles of one another, so communicating with each other works, but it’s hardly secure.

  2. The writer has established an excellent foundation for this series of articles. Note his discussion on “common usage technologies” CB radio and the use of “non licensed devices”.

    The key is to communicate, which includes the ability to listen (monitoring) when transmitting may be ill advised.
    As usual, I am very much looking forward to this series of articles.

  3. 1) Re the Dead zone, the military found in Vietnam that wet jungle vegetation could cut the groundwave transmission to just a few miles , giving a big gap out to the 300 mile line where skywaves bounced back to earth.

    2) So they used a teepee-like NVIS antenna to send the transmission straight up to bounce off the ionosphere and back down, thereby giving good reception in the dead zone out to about 70 miles. Works mainly with 2-8 Mhz, depending on time of day and conditions.

    3) For vehicles, a NVIS-like effect can be reportedly be acquired by bending a tall vertical antenna over to the horizontal –e.g, with a cord connecting to the opposite bumper.

    1. Don,

      Thanks for the Vietnam example. Later in the article, I will cover NVIS to some degree, along with the impact that terrain, sun cycles, and time of year has on RF communications. This is why testing and practice are so important.

      Not to get too far ahead of myself, but using NVIS requires both sites to have an NVIS setup. I have a neighbor about 30 miles away, and I have an NVIS config on 80 meters. He can hear me fine, I can receive him at a level just over background static. Why? Because he doesn’t have an NVIS setup. Test, test, and retest.

      Lee, I will talk about the need for large frequency coverage across multiple bands, and getting equipment that covers critical frequencies, as the article progresses, but excellent point.

      Jason, consider yourself very lucky to get 15 miles on a CB especially on a rig without SSB. You must have great terrain working in your favor, or have an amp, (for emergency use only of course). I’ll talk more about CB hardware and options soon, along with comparisons with other frequencies.

      Encryption, and frequency hopping technologies exist, but keep in mind that they are legally “fuzzy” when it comes to the FCC. I will make a reference to it when discussing packets and email transmissions over HAM bands.

      Thanks for the feedback everyone, and for those just reading, feel free to ask questions.

  4. Thanks for kicking this off , Robert. I keep urging my groups to get trained and get licensed. I understand the reluctance to add another government data point onto our lives but getting licensed entails both training and entrance into an enormous asset network. That network includes both human and material resources but the net result really is about individual skill development to implement each of them.

    I get weary of folks who keep saying things to the effect of, “start operating when SHTF” both sans license and sans training/experience. That’s the same logic about getting any skill….seriously flawed logic.

    I’m grateful some of my groups have members who are now licensed and engaged. Be proactive. Become radio operators for the formal emergency networks. Take control. Become community influences. Shape the norm.

    Best wishes and God Bless,

    1. Thanks Wheatley, I hear that a lot too. I’m even guilty of it. I pushed off getting licensed for a long time, using confiscation issues, FCC, and anonymity as an excuse when in reality I just didn’t want to take a test.

      I saw those questions about electronics and most went right over my head, until I applied myself and started learning. I had zero background in electronics, ohms law, and couldn’t tell you what a capacitor was.

      I didn’t realize that the test was setup in a way where you can just memorize the answers. Of course, learning is best but for those without an electronics background it’s a easy way to start.

      Heck, if I can get a general class license, they anyone can.
      That’s why later in the article I have a whole section on getting a license and why it is so important to be able to actually use the equipment and not just buy something on amazon and put it away “for emergency use.”

      If I have one goal here, it’s to encourage people to get their license and to start using and learning their radios. 73

    1. The term “Jamming” is more of a movie thing. Some evil government agency flips a switch and then you can’t communicate. In reality, you can still transmit and receive.

      The issue known as “Jamming” is the result of their signal being so strong that you can’t hear anything else. Kind of like when one person whispers in your right ear while someone is yelling in your left ear. Keep in mind that the person you are talking to might not even hear the “Jammer”

      This happens all the time on a frequency without any kind of intent behind it. People use the same frequencies but they can’t hear you so they continue like you aren’t there. You can hear them, and the person you are trying to talk to, but they start stepping all over the one you want to chat with because their signal is much stronger.

      Even natural electrical phenomenons or a bad light bulb, socket or just poorly insulated AC wires can have the same impact.

      There are two basic solutions around this. If the problem-ed source bandwidth is narrow enough you can use noise blanking and filters to block out your receiving of their signal. The second is even simpler.. change the frequency to something you have previously agreed on.

  5. i am a licensed ham operator with a general license and most of all operators will not talk to an unlicensed operator except under dire emergencies! just saying!!

  6. I took the first test. Personally, I regret mumbling my way through log and scientific notation in high school. We have a 10 meter net on Mondays. Took me four weeks to finally connect and register as a check-in. Antenna orientations and power sources all have to be in line. Pretty sure NVIS does not work at 2, 6 and 10. My Elmer set me straight on that one. Fine people in Ham clubs with whom you want to be associated.

    1. RV
      You are correct, NVIS does not work for 2 meters and 6 meters (both being VHF with 6 meters having some HF properties). For 10 meters it would depend on many propagation factors so I would put that in the “almost always no” category.

      Both the 2 and 6 meter bands, along with 10 have additional propagation methods that are sporadic, along with EME (bouncing signals between the earth and moon) for 2 Meters all the way through Microwave bands (not 10m). We will cover those to a greater extent as the article progresses.

  7. Thanks Robert for this important and nicely presented information. Folks should know there’s a bit more to all this than just picking up a radio and pressing TALK. Good work and very much looking forward to the rest of your installments! 73

  8. preppers seem to have this notion that they’ll buy some equipment and stash it in a metal trash can for “someday” when there’s no FCC, and then they’ll be able to communicate. I hate to break it to you, but ham radio is called a “hobby” because there’s a lot to it. If communication is important to your plans, I suggest you get your ham license and start using this stuff NOW, so that you’ll know how when (if) the time comes during your lifetime. And if the end doesn’t come in time for you? Bummer, you only had a hobby. Although you will need to provide your address to a government that already has it, you can specify a PO box for public info.

  9. I am a 62 year old lady with little background in electronics. I just got my general ham license. I had to study hard, but it was worth the effort. It can be done folks; don’t let the test scare you. I found studying with flash cards available for free on the internet to be most helpful.

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