Friday, July 19, 2013

Two-Way Radio Communications


In many SHTF situations, normal communications will be disrupted. Telephones depend on transmission lines, cell phones depend on powered cell towers, and e-mail depends on the Internet—none may be available. While even your own personal radio powered by the sun may be destroyed in an emergency, history reveals that in many disasters personal radios are about the only two-way communication method that does work. Radio communications can be useful for keeping a convoy cohesive, for security, for a team checking for injuries door-to-door, for a family keeping in touch while foraging for food, water, or firewood, or for a team to coordinate rescue or defense actions.

I’m a licensed amateur radio operator, a “ham.” After a killer earthquake hit the Asian city where I lived, one of my friends--a ham with a high frequency (HF) "shortwave" radio, a directional antenna, and a generator--was the only way the outside world (including government agents) had to communicate with our city. I want to share some of my perspective on FRS/GMRS “walkie-talkies,” CB radio, and amateur radio.

Note: This article is written from a USA perspective. Conventions, frequencies, and laws may not be the same in other countries.

FRS/GMRS

You may be familiar with FRS/GMRS radios as the inexpensive walkie-talkies found in such places as Walmart.

Family Radio Service (FRS) radio offers 14 channels of low-power frequency modulated (FM) ultra-high frequency (UHF) radio communication that has been adopted as a low-cost alternative to business-band radios. FRS radio communication does not require a license from the FCC when used according to FRS rules.

One feature of many FRS radios is sub-audible tone squelch which allows the use of privacy codes. This allows the same channel to be used by more than one conversation at a time without the conversations interfering with one another. (Privacy codes do not actually grant privacy, as anyone can enter any code to hear whatever conversation is in progress using that code.)

FRS radios have fixed antennas, a feature intentionally designed to keep communication ranges short to allow for more users. While there are table-top FRS radios with better antennas, practically speaking one should consider FRS radio for situations where parties are no more than a mile apart: vehicle convoys, within a large building, on a cruise ship, on a modest campus, etc.

General Mobile Radio Service (GMRS) radio is also FM UHF, like FRS, and shares the FRS radio band. GMRS radios are generally more expensive than FRS but have more to offer and are typically of better quality as well. GMRS requires a license in the USA (but not Canada). A licensed adult may communicate with his or her immediate family members without them also needing to be licensed, but in a business setting the owner’s license does not extend to other employees. Acquiring a GMRS license is as simple as filling out the application and paying the fee; no test is required.

One advantage GMRS has over FRS is range; while FRS is limited to 500 milliwats (0.5 watts) of power, a GMRS radio can operate at up to 50 watts, depending on type. In radio communications, power equals range. Expect GMRS handheld radios to function best with a range of 1-3 miles. GMRS radios may have detachable or external antennas, further extending their range and clarity. Finally, the use of repeaters is permitted in GMRS. A repeater acts as a high-power intermediate radio with a high-gain antenna which greatly enhances the range of lower-power radios using the repeater to communicate with one another.

GMRS radio has 15 channels, 7 of which are shared with FRS. GMRS licensees may conduct voice communications on the shared FRS channels at a maximum power of 5 watts—still ten times the power a FRS radio may employ. Hybrid radios are available which include all FRS and GMRS channels, and which use the shared channels in either FRS or GMRS mode. When using a hybrid radio, a license is not needed to communicate on a FRS channel under FRS rules.

FRS/GMRS has a role in emergency communications, particularly among family or team members within relative proximity to one another. When selecting a radio, be sure the equipment you purchase supports the application you desire; not many options are available, for example, that support the use of repeaters.


CB Radio

Citizen’s Band (CB) radio is a license-free high frequency (HF) radio communications system in which business and personal communications are permitted. CB radios are limited to 4 watts (measured at the antenna connection), and make use of 40 channels. Communication is either via amplitude modulation (AM), or single side band (SSB); each channel can filter out a lower side band (LSB) and an upper side band (USB). That 4 watts of unmodulated carrier power ends up being 16 watts under AM or 12 watts for SSB. By using a SSB, transmission power is concentrated into a narrower frequency, for less interference.

Any given channel can only support one mode of communication at a time. By convention channels 1-35 are used in AM mode and channels 36-40 are used in SSB mode, with channel 19 the choice of truckers and other highway travelers. Channel 9 is reserved for emergency communications and roadside assistance.

Very popular in the 1970’s, CB radio was the victim of her own success. Many business users moved to business-band radio, where the few users sharing a frequency and the higher power allowances made for a more workable solution. Cellphone technology also took its toll on the CB radio’s popularity.

CB communications are affected by skywave propagation factors which can sometimes make short-range communication even shorter, while enabling oddly long-range communication—thousands of miles between radios! Under normal conditions, one may expect reliable CB comms from 1-10 miles, depending on power and antenna. Lax FCC enforcement, however, means many operators use linear amplifiers to greatly increase their transmission power and range. This is annoying when it interferes with the communications of those abiding by FCC rules. For the same reason, it is common for CB station operators to intentionally seek to communicate beyond 160 miles via skywave propagation. Freebanders modify their CB radio to illegally transmit out of band.

The antenna is extremely important if you want to maximize your range on the CB band. There are omnidirectional antennas that work well in all directions, and directional antennas that work better in one direction at the expense of other directions; there are 9-foot tall quarter-wave whip antennas, and shorter antennas with loading coils to match the impedance of a longer antenna. Be sure to consider your usage requirements before selecting an antenna.


Amateur Radio

Amateur or “ham” radio requires at least one of several licenses for USA operation, limited to non-commercial communication, experimentation, learning, and emergency communications. Getting a license requires passing a test of one’s technical knowledge of electronics, radio equipment, antennas, and radio propagation, as well as familiarity with government regulations. Licensed amateur radio operators (“hams”) are issued a call sign for identification. Amateur radio includes voice, text, image, and data communications, and frequencies are allocated from across the radio frequency (RF) spectrum—high frequency (HF), very high frequency (VHF), ultra-high frequency (UHF), and microwave. Proficiency at Morse Code is no longer required for an amateur radio license. There are three license levels in the USA; each level provides access to larger portions of the RF spectrum. The lowest level license, Technician Class, provides access to UHF and VHF bands plus the 6-meter band and the 10-meter band (similar to CB radio). (Click here for help free online help preparing and practicing for your Technician Class license.)

Amateur radio operators can transmit at high power (up to 1,500 watts). They can use any frequency within their allotted bands, rather than keeping to specific “channels.” With frequencies available across the RF spectrum, they have choices appropriate for local, regional, or worldwide communications (though voice communications at world range frequencies are usually reserved for the license levels beyond Technician Class).

Amateur radio makes liberal use of repeaters, and repeaters linked with other repeaters, so even Technician Class hams can communicate around the world with just a relatively low-power handheld radio. This is also possible through data networks that incorporate the Internet in their propagation. Amateur radio also has its own communications satellites, and hams communicate by skipping signals off various layers of atmosphere or bouncing signals off the moon, the aurora borealis, or even the ionized trails left by meteors.

While in an emergency situation radio communications in general may be obstructed (by lack of power, damaged antennas, limited or no Internet access, etc.), many amateur radio operators are prepared to operate in “emcomms” (emergency communication) mode, using alternate energy sources, mobile repeaters, digital radio networks, and more.

There are amateur radio clubs all across America, and the ham culture encourages “Elmers,” experienced hams who help mentor new hams. In most regions there are emergency radio nets all set up where radio operators check in weekly and practice identifying themselves in the queue and passing on messages.


Summary

What's the best choice for an emergency? Personally, I'm going with both ham and FRS/GMRS equipment, but a case could be made for having all three.

FRS/GMRS
  • Pros: cheap, no special knowledge required, personal and commercial traffic OK, most other users, no license (FRS) or no test for license (GMRS)
  • Cons: shortest range for reliable communications

CB Radio
  • Pros: not too expensive, no special knowledge required, personal and commercial traffic OK, many other users, no license required
  • Cons: short range for reliable communications

Amateur Radio
  • Pros: flexible, longest effective range, data- and picture-capable, enthusiastic community
  • Cons: special knowledge required, license required, personal or emergency communications only (no commercial), can be expensive, less common than FRS/GMRS or CB

Related articles:
Satellite Technology for Emergency Communications
Seven Advantages of Amateur Radio

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1 comment:

  1. A great article on frs and gmrs radios. With the times we live in, a backup radio such as frs and gmrs could serve in a time of national emergency.

    ReplyDelete