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: http://www.dsmt.com/resources/ip-rating-chart/ .
- 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.
- 2 – Radio Communication Methods During Emergencies, by R. in NC
- 3 – Radio Communication Methods During Emergencies, by R. in NC
- 4 – Radio Communication Methods During Emergencies, by R. in NC
- 5 – Radio Communication Methods During Emergencies, by R. in NC
SurvivalBlog Writing Contest
This has been part 1 of a 5 part entry for Round 73 of the SurvivalBlog non-fiction writing contest. The nearly $11,000 worth of prizes for this round include:
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Round 73 ends on November 30th, so get busy writing and e-mail us your entry. Remember that there is a 1,500-word minimum, and that articles on practical “how to” skills for survival have an advantage in the judging.