Radio Communication Methods During Emergencies- Part 3

from Survival Blog:

We just took a look at non-FCC License Dependent Communications, including use expectations and purchase considerations. Today, we begin examining FCC license dependent communications devices.

FCC License Dependent Communications

GMRS

GMRS radios operate on the same frequencies as FRS along with a number of additional channels. They can use up to 50 watts, and the FCC allows for better antennas and repeaters. GMRS will require a license. No test is needed, and the FCC license covers all residents of a household. On last check, the license cost $85 dollars. Pros and cons, along with distance, are similar to FRS, with the exception of additional power, use of repeaters, and better antennas. (See FRS radios for details.)

Amateur Radio – Ham Radio

Ham Radio Overview

Ham radio covers frequencies ranging from 135 kHz to above 275 GHz (as of March 28, 2017). The range of frequencies is immense and covers a wide range of possible communications distances. In addition to the features of each band of frequencies, Ham radio operators have access to satellite-based communications and EME (Earth Moon Earth) bouncing. EME is a technique where signals are bounded off of the moon to a distant location. As long as both antennas can point to the moon at the same time, this can greatly extend range (though it requires significant amounts of power and special antennas). Satellite access is typically setup as a repeater and/or APRS. (See below for information on APRS.) It is even possible to chat with astronauts on the International Space Station (ISS) when they are overhead and on their Ham radio.

 

Various Ham Radio Methods of Communicating

Methods of communicating over frequencies vary too. They can include Analog AM/FM, Digital Voice, packets, TCP/IP, texting, email, file transfer, and CW (Morse Code), to list just a few. There are even Internet integration technologies, such as D-Star and Echolink, that will allow you to use software on your computer or radio to connect over the Internet to repeaters across the world. Ham radios can be combined with GPS and Internet gateways to send text messages to cellphones and email accounts from a handheld two-way radio. Winlink and other programs can send out email from your computer without Internet access, by using radio waves to carry the email to a remote email server or radio to radio.

As for encryption, there are several opinions of the law around this. Some say you can’t use encryption, and some point to sections of the FCC laws that describe the need to document your method of encryption but not your decryption keys. Since I’m not a lawyer, I won’t advise either way. I will note that a popular method of emailing via radio called Winlink does uses encryption. Winlink is used for both emergency and normal Ham radio communications.

Different Ham Radio Classes of License

Different classes of license have different levels of access to these methods on specific bands. Some bands are better for distance at different times of the day or night. Almost all are impacted by the solar cycle and sunspots.

Day/night Communications

Day vs night communications are all about bouncing radio waves off of the ionosphere. There is some impact with ground waves; however, it mostly concerns what layer of the ionosphere absorbs and reflects what frequency. Since the layers change between day and night, the absorption and reflection will change for each frequency.

  • Higher is the larger number in meters, not MHz (i.e. 30, 40, 60, 80 meters are higher than 20 meters).
  • 10.1 MHz (30 Meter band) and higher are better for night time.
  • 14 MHz (20 Meter band and below – to 12 meters) are better in the daytime.
  • 28 MHz (10 Meter band and lower to 6 Meters) are better in the daytime, and they are very close to line of site propagation. Sky wave propagation has an impact but usually not during a solar minimum (or the 2017 current solar maximum).
  • 144 MHz (2 Meters and lower) are line of sight and not really impacted by day/night differences.

Groundwave Distances and Frequency

Groundwave is what it sounds like. The radio wave spreads out along the ground, from the source antenna. This happens in parallel to sky wave propagation. The difference between groundwave and line of sight is that when a radio wave is about 6 meters or longer, it starts to follow the curve of the earth. For 6 meters, this curve past the horizon is minimal. For 160 meter waves, it can be out to distances near 100 miles. The following distances are very rough guidelines. Also note that these distances do not include sky wave distances. These are literally ground wave only approximations under good conditions.

  • 1.8 MHz (160 Meters) 90 miles
  • 3.5 MHz (80 Meters) 70 miles
  • 7 MHz (40 Meters) & 10 MHz (30 Meters) 40 miles
  • 14 MHz (20 Meters) 30 miles
  • 21 MHz (15 Meters) 30 miles
  • 28 MHz (10 Meters) 20 miles

Dead Zones

When radio waves bounce off the ionosphere, they do so in an inverted “V” pattern, over and over again. At the point where the wave is in contact with the ionosphere, it is not in contact with the earth. Think of it as a ball bouncing. Where the ball hits the ground, you can communicate; when it is in the air you cannot. The exception of this bounce is when you are within the range of groundwave. This bounce distance varies, because of a few things: angle of takeoff (based on type and height of the antenna), day/night ionospheric absorption of the radio wave, and the shape of the ionospheric layer itself. Do not think of the ionosphere as a smooth line in the sky; think of it as bouncing radio waves off of a rolling sea.

Because of dead zones, ionospheric absorption, terrain, and distance, developing a communications plan for a survival situation is not so much a matter of just saying what radio we will use or what frequency/wavelength those radios will operate on, as it is about having layers of backup plans. What frequency and wavelength will you attempt communication over first, and at what time will that occur? If unsuccessful, what frequency/time will be attempted next?

Note: I live in central North Carolina, and I have a horrible (I mean stealth) antenna setup. Using 80 meters at night, I can communicate with the “VA fone net” (one of the oldest Ham radio “nets” in the country, and located in Virginia). This is with a G5RV antenna setup in my basement (NVIS with overhead obstacles) and wrapped around at odd angles. We are generally talking about a 200-300 mile distance before my signal gets too weak. I can hear people in Canada, New England, Florida, Louisiana, and Texas. I’ve even seen packets come in from Cuba, Argentina, and Poland, but I cannot usually hear people 100 miles away.

Flexibility is the key to success here. Different distances vary based on what band/wavelength I am operating on and environmental conditions.

Radio Equipment

There’s more to sending and receiving data and voice over the airwaves than just an antenna and a radio. Before making any HF purchases, I recommend that you read the book Your First Amateur Radio HF Station from ARRL, ISBN: 978-1-62595-007-9. This book will give an excellent overview of what is needed and why and how to set it up.

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