Communications FAQ PT2

A. Types of communications

1. Wired Communications

a. Basic Telephone Service

Current telephone communications, at least in industrialized nations, is the standard of excellence that most communications systems are compared. Disparaging comments and annoying customer service issues aside, standard phone service is nearly universal, approaches 100 percent reliability, and offers nearly instant connectivity to virtually any person in the industrialized world. Phone service is probably the single most utilized form of survival communications, used whenever 911 is
dialled, or a person phones a friend for help.

While basic phone has never been completely secure, it’s become very apparent that phone services are approaching a nearly total security compromise, at least with respect to national agencies. Note that with modern
signalling and billing records systems, every phone call is logged, and the phone number, which is effectively an address to a physical location for wired phones, is present with each call; this is true even of pay phones.

The exposure risk associated with basic phone systems is extreme. Any communication which is intended to remain private probably shouldn’t rely on phones. This is of no bearing for most conventional survival scenarios.

Phone service can fail at any time, but due to very good survival engineering, basic phone service often stays operational days after AC power fails. Destruction of inside plant (central office switching equipment, batteries, and power generation) or outside plant (poles, wiring, and transmission equipment) will result in failure of service, of course. Note that in floods, hurricanes, and earthquakes phone service often fails in a widespread way, whereas failure in common storms and civil disorder is usually localized.

Note that while phone service may continue to be reliable during a disaster, communications may be difficult due to overloading. During the summer of 1996, a power outage in the Western United States resulted in a flood of calls to 911 systems in several states from people simply reporting that their power was out; in some areas, 911 failed completely, or had hold times in excess of 30 minutes.

b. Private Point-to-Point (Intercoms and Field Phones)

Outside of PBXs located in buildings, private wired communications aren’t very common. Two notable exceptions are intercom systems that are used to communicate within a building, and field phones, which are essentially military versions of intercoms. Intercoms are generally limited in range.

So-called wireless intercoms use the AC power line to convey their signal, and are generally dependent on AC power themselves. Wired intercoms usually don t cover more than a few hundred feet in a building, due to the wiring difficulties. Such intercoms usually run on batteries. Field phones are generally used in environments where complete control of the lines of communication exist. The typical military field phone runs on two D cell batteries, and can operate over up to twenty miles of two-conductor wire.

In general, private wired communications is the most secure. The wires themselves can be followed if not concealed, revealing both points of communications.

2. Radio Signals

There are a huge number of possible options for radio-based survival communications, ranging from getting broadcasts from authorities via a $4 AM radio to portable satellite phones.

a) Broadcast Radio

AM Radio
Let’s be blunt. If you can have only one radio, if you have less than ten bucks to buy equipment, forget CB, Ham, and everything else. Get a portable AM radio. The first radio band for survival, news, and government information is the old AM radio band, from 550 Khz to 1700 Khz.

Equipment can be very small, with typical radios 1×3x4 in size, light, low-power (two AA batteries can run a radio for weeks at low volume or with earphones), cheap (Radio Shack’s FlavorRadio is $7), very reliable (single IC), long range (100s of miles for clear-channel radio stations at night)

In addition to the radios themselves being reliable, AM broadcast radio stations themselves are also fairly reliable with back-up transmitters, emergency generators, and bomb shelters: a few radio stations in every area are part of a extremely reliable network that is a carryover from the civil-defense radio network’s heydays of the 1950’s. The two civil defense frequencies are 640 Khz and 1240 Khz. As a result of the defense network carry-over, and the fact that many AM stations offer talk-radio call-in formats, AM radio is ideal for getting news and information during emergencies, probably more so than any other source.

The military and other government agencies also maintain emergency portable radio stations for disaster-stuck areas, that are AM stations. Inexpensive AM radios with ferrite bar antennas have a secondary survival use as navigation instruments. Such radios have sharp, well-defined nulls where the signal goes dead. If one knows the direction of the nulls of the radio and the locations of the AM radio stations in the area, it’s possible to triangulate your own location based on the directions your radio indicates each station is in. Accuracy isn’t incredible, but it can generally give a position of +/- 5 miles if the radio stations are 50 miles away.

Within the US, there was originally a set of stations set up with what is known as clear channels that made sure a single, high power station had no others within hundreds of miles on the same frequency. Currently these are known as Class A stations (which run 50,000 watts). These stations can be heard for hundreds of miles at night, allowing listeners in disaster-striken ares to hear stations that are in surviving areas. (for example: At night, one can hear WMAQ, Chicago on the eastern edge of the Colorado Rockies without much difficulty.) Refer to Appendix A for a list of Class A Clear Channel stations.

b) Two-Way Radio

Unlicensed Services

All radio services are regulated in some form, even if it’s a law that states that the service is unregulated. However, there are several license-free services in the U.S. Note that other locations aren’t quite as progressive in terms of unregulated services. The U.K., for example, requires CB radios to be licensed, and doesn’t offer a free 1750 meter band. YMMV!

CB Radio (AM and SSB)

CB, also known as Citizen’s Band (or Children’s Band to its detractors) uses an amplitude-modulated signal on forty channels centered around 27 Mhz. These radios are limited by FCC regulation to four watts of output power going up the antenna. Typically, from a vehicle with an average antenna on flat terrain this results in a reliable range of ten to twenty miles.

With a better antenna, considerably longer ranges are possible. However, another FCC regulation requires CB operators to take steps to prevent their signal from being detectable beyond 150 miles. CB frequencies are plagued with a number of problems, such as overcrowding on certain frequencies and considerable rudeness.

Typically, Channel eleven is considered a general calling channel, and Channel nineteen is used by truckers. In addition, Channel nine is reserved by law for emergency use only.

Refer to Appendix B for a list of Citizens Band Channel Frequency assignments.

Part 15 Radio Bands

So-called part 15 bands owe their name to the United State’s Federal Communications Commission, which has a set of rules (Part 15) which allow certain types of unlicensed radio transmitters. There are three main part 15 bands that are commonly used for two-way voice communications (other bands exist under part 15 for a plethora of other devices.) The only band that’s really significant is the 49 Mhz band; the other two are interesting, but probably impractical.

49 Mhz Radios

The 49 Mhz band is a widely-used consumer radio band, primarily for cordless phones. There are 10 narrow-band FM channels between 49.67 and 50.00 Mhz assigned to the band (Refer to Appendix C). The band is relatively noise-free in non-industrial areas, though the millions of cordless phones means plenty of interference in highly urban settings. Power output is specified by field strength, 10,000 uVolts/meter at 3 meters, and translates to a few milliwatts. The band is most useful for short-range communications.

The receivers of good radios are such that this low power gives a 1/4 mile range, though field tests show ranges of 1/8 to 1/2 mile, depending on terrain. The radios perform amazingly well in difficult, hilly terrain at short range. In very controlled tests using a lab-grade receiver/antenna, a detection range of three miles was obtained. Equipment is small and light, often only 1×3x7 or smaller; it’s offered by many manufacturers that also make CB radio equipment. Power requirements are miniscule, with RX requirements of less then 20 milliwatts and TX requirements of 100 milliwatts. (In one test with a radio using three AA lithium batteries, run time in RX mode was two WEEKS continuous.)

Though very reliable electrically, durability is a concern, as most equipment is built with light plastic cases and no waterproofing. Cost is generally $25-$40 per unit with features of single vs. multiple channel and voice-operated switching accounting for the cost difference. Note that kiddie walkie-talkies also operate on this band but the receivers of such radios are worthless.

Due to the proliferation of small, inexpensive 2-way radios for this band, there is no realistic hope of private communications-indeed, it’s entirely possible that this band will become so crowded as to be useless in the event of an emergency.

In addition, there are no standard frequency uses or nets on this band. Considering the limited range, the primary use will likely be for tactical communications among a small group, such as coordinating camp activities. One group sends a scout ahead in difficult terrain while the rest of the backpacking party waits, with the scout calling back if the path taken is viable; this saves hours of useless backtracking.

A secondary use is to place a radio with volume set on maximum on a pack that is cached in a well-camouflaged environment. The squelch keeps the radio quiet, but another radio can transmit sounds allowing the user to home-in on the hidden pack.

The 49 Mhz band is smack-dab in the middle of the VHF-low band (30-88 Mhz, 25 Khz channel spacing) that the military use world-wide for primary tactical communications. It should be no surprise then that there’s quite a variety of ground-based, airborne, and satellite-based radio equipment dedicated to intercepting, direction-finding, and jamming these frequencies, which include the 49 Mhz band.

Theoretically, consumer 49 Mhz radios and military VHF-low radios should interoperate. However, the reality is that only some military radios operate with narrow band FM, and the tuning steps of the radios are 25 Khz at best, frequently placing them off-channel.

Newer tactical radios, such as the US Army SINCGARS (Single Channel Ground and Airborne Radio System, are usually operated in frequency-hopping mode, in which there is no hope of inter-operability (such radios can however be tuned to single channels)

Although highly susceptible to interception and direction-finding, in practice the range of consumer radios on this band is so limited that this highly unlikely to occur unless a party is expressly searching for the signal in the immediate area; the short range also makes these one of the few radios immune to satellite-based DF. In urban environments there are literally hundreds of competing signals on the same frequency, making interception and DF difficult. Note that in scenarios involving military conflict, operational jammers could make these radios unusable at tens of miles away, and these radios are likely to be unintended victims, jammed simply because they’re in the middle of a military band, and not due to overt intent.

One group known to us has primary communications based on 49 Mhz radios. The limited range and extremely low power consumption were keys, along with the fact that the group stays close together 100% of the time were factors that lead to the decision.

460 Mhz Family Radio Service (FRS)

The FRS radio service is a recent addition in the US and a good selection of low cost equipment is available. The radios are relatively low power 500-600 milliwatts (0.5-0.6 watts), and operate on 14 channels in the 460 Mhz frequency range using reliable FM modulation. The radios have a user settable squelch level control to minimize interference. In addition, the radios utilize a system known as Continuous Tone Coded Squelch System (CTCSS) which allows an additional degree of interference control. These radios have a useable range up to 2 miles depending on terrain conditions. Refer to Appendix D for a list of FRS frequencies and Appendix E for a discussion of CTCSS.

1750 Meter Lowfer Band

In the US, the 1750-meter band allows radios to operate with 1 Watt of power into a 50 foot long transmission line/antenna system at frequencies in the 170 Khz (that s 0.170 Mhz) range with no license. This is a *really* low frequency.

Equipment for 1750 meters is generally as small as one wants to build it. There are only a few commercially built radios for this band, generally the same size and weight as a larger mobile CB radio. Power consumption is quite low, with about 3 watts peak for TX and hundreds of milliwatts at most for RX. Cost is generally no more than $200 for a top-end commercial built radio.
Antennas are inefficient and large, since the 50 foot limit really needs to be exploited for the radio to work well. Communication is therefore not very reliable at long ranges; however, at short ranges (a few miles) at night, when the noise level is low, 1750 meters is reliable. At night during the winter, it provides the greatest range, with reasonably reliable contacts at 100’s of miles. During the summer this band is plagued with static making it rather unreliable.

The 1750 Meter band is a (barely) plausible survival radio band only if it’s used for a network among users that are located near each other.

There are a few experimenters on this band that perform low-rate data communications using exotic modulation methods, but most prefer Morse code or SSB. There are no regularly monitored channels or survival networks in operation, though some radio enthusiasts in California do have a regular net.

It is, however, worth noting, that some caving and spelunking enthusiasts also sometimes use this band, as low frequencies have some limited ability to penetrate obstacles such as the ground. (The same principle is used by the US Navy, which uses VLF and ELF signals to contact submarines)

There’s one survivalist of note that does use this band: the U.S. Government. A special high-survivability data network known as the ground-wave emergency network, or GWEN, can be heard between 150 and 170 Khz with a repetitive noise that sounds like a cross between a hiss and a crunching sound. This network is intended to survive a massive nuclear strike and provide low-data-rate post apocalyptic communications.

Low frequencies are so easy to direction find that they are the basis of the first radio-navigation system used for aircraft and ships. Starting at about 200 Khz, there are thousands of low-power non-directional beacons (NDBs). Automatic-direction-finding (ADF) radios tuned to an NDB indicate their direction with high accuracy, and many ADF receivers are capable of tuning the 1750 meter band.

On the plus side, although direction-finders work really well here, the low power and low frequency of the 1750 Meter band make it effective for covert communications; few receivers tune this low, and even fewer people even bother to listen. Due to the inefficiencies of the antenna system jamming is difficult, and there is no known deployed jamming equipment capable of disrupting this band.

Micro-power AM and FM
Also permitted under part 15 is low-power (100 milliwatts) AM transmitters with a 10 foot antenna restriction on the same band as broadcast AM radio.
The AM band shares many characteristics and difficulties of the 1750-meter band. Equipment is generally always hand-made, usually from AM broadcast kits. Receivers can be cheap AM receivers, but a viable communication system will likely use a sensitive medium wave or short wave radio receiver. Cost of the transmitter can be as low as $20, the receiver $5 to $5000.
Transmitter size is generally the size of a small mobile CB, about 2×6x6. Power consumption is minimal, under 1/2 watt. Reliable reception ranges of a 1/4 mile or so are common, though with good receivers and quiet band conditions (at night, during the winter time) on an unoccupied AM channel (rare in its own right) ranges of 100’s of miles have been obtained.
Signals are easy to direction find (indeed, many aircraft ADF systems also tune the AM radio band) and it s trivial to jam weak-signal reception in the AM band when Mother Nature isn’t doing it herself with thunderstorms.
No nets are known to use micro-power AM, though some pirate-radio broadcasts violate the FCC’s power specification and some of these transmit vaguely survival-related gloom-and-doom conspiracy radio programming. This (with legal power, and probably better, community-related programming, of course) is probably the only viable use for this band in a survival context (weak as though that may be.)
Micro-power FM stations are also permitted, but the large bandwidth and low power allowed makes micropower FM even more useless than AM.

c) Licensed/Regulated Services

(i) Amateur ( Ham ) Radio

The bands listed below all require a license for use in the United States and most other countries with one important exception: Under US law (Part 97 of the FCC regulations), a station may lawfully use any and all means at its disposal to locate help in the case of a legitimate emergency.

6-Meter Band

The six-meter band (50-54 Mhz ham band) is considered sort of a “schizophrenic” band, that can’t make up its mind whether to be a worldwide/distant contact band or a local VHF band. It generally has been known to be used as both of these. The use of this band is primarily a local phenomenon-extremely popular in some areas and completely silent in others.

2-Meter Band

2 Meters (144-148 Mhz.) is one of the most commonly used bands in the United States. Frequently these days, when a ham buys his first radio, it’s a mobile or handheld 2-meter FM transceiver. SSB and CW are rarely, but occasionally used on this band. However, 2M is a favorite for amateur radio satellite and amateur Earth-Moon-Earth communications, and for technical reasons these methods require the use of SSB or CW rather than FM. This band, along with the 70-centimeter (432-450 Mhz) band, are among the most popular bands for local packet (data) radio communications, and are also hands-down favorites for Radio Amateur Civil Emergency Service (RACES) and Amateur Radio Emergency Service (ARES) communications. Licensure for the use of the above three bands in the United States is granted on the basis of two multiple-choice written examinations covering radio theory, amateur practice, and FCC regulations. The ARRL (website address above) maintains a list of examination sessions, and study guides for these exams are on the shelf in most libraries and bookstores.

MF/HF Bam Bands

In the United States, ham radio bands exist at 1.8 Mhz, 3.5 Mhz, 7 Mhz, 10.1 Mhz, 14 Mhz, 21 Mhz, 24 Mhz, and 28 Mhz. These bands are all capable of long-distance communications, depending on atmospheric and sunspot conditions, and have all been used for worldwide communication. The most common emissions modes are CW (Morse Code) and Single Sideband, but certain data communications are also used. Equipment for these bands is all over the range in terms of price and complexity-low-power CW-only single frequency transmitters can be built for $20, and high end all-band all-mode transceivers can be bought for several thousand dollars. Literature on use of these bands is common, with “Low-Profile Amateur Radio” by Jim Kearman being an excellent (if basic) primer for people who want an introduction into low-power HF operation without much in the way of an antenna. A license from Federal Communications Commission is required to transmit on these bands (with limited exceptions explained above), and the license is based upon examination of the licensee’s understanding of radio theory and law, and ability to receive and understand signals in the Morse code.

3. Commercial Carrier and Emergency Services

Cellular Phones

A Cellular phone is essentially a low-power UHF transceiver. When a call is made, the phone signals a fixed station called a ‘cell.’ The cell transfers the signals between the radio waves and the phone exchange. (A gross oversimplification, but detail is not required here). Cell phone conversations are not private, any more than any other radio conversation. Technically, the law says that they may not be monitored, but this law is unbelievably easy to violate. Scanners able to pick up cell frequencies are not sold to civilians any more, but they can be built.
Cell phones also depend upon a working cell. A power outage for an extended period could result in shutdown. Also, cells can be overloaded. In the event of a disaster, a cell can handle a given number of calls. Calls that exceed the cell capacity will be rejected, rendering communications ineffective.

Paging

Paging is essentially a method of one-way radio communication. An individual makes a telephone call to a given phone number, and is prompted to enter a message. This message is then sent out over VHF or UHF radio to a specific pager. Some paging service allows the display of phone numbers.
Others actually permit one to email a message to a pager. This service has an advantage, in that it can discreetly summon one to check in or go somewhere as needed, but is dependent upon a network of transmitter towers and phone lines, and therefore might not be fully functional in a disaster. In June of 1998 the complete failure of the Galaxy IV satellite caused a shutdown of 90% of the pagers in the continental US. This single point failure shows the fallacy of relying on a single comms system.

4. Radio Operation and Procedures

A radio-based communication system depend on two main elements to work: operational radio hardware, and procedures that allow the sender and receiver to communicate.

a) Radio Equipment, Antennas, and Propagation

The dB or decibel (1/100th of a Bel) is a comparative measurement based on a log scale. That is, there’s something measured against a reference. The decibel allows a very wide range of signal power to be represented with small, manageable numbers:
Power Change Decibels
2X 3 dB
100X 20 dB
1,000,000X 60 dB
0.5 X -3 dB
0.000001X -60 dB
Things that increase a signal are usually called gains and things that decrease a signal s strength are called losses, and both are usually measured in dB, with gains being positive and losses negative. Note that if we compare power to a fixed reference, such as a 1 Watt or one milliwatt, the dB can also be a measurement of actual power; a transmitter with a 20 dBW output, for example, has 100 Watts of power.
There two major factors that determine total radio performance, known as station gain (what the equipment does) and path loss (what the environment does to the signal between the stations.)
It may seem confusing, but it’s as simple as this: If station gain is greater than path loss, you can communicate, otherwise, you can’t. If you can’t communicate, you need to fix one or more parts of the radio system until you have enough station gain. Use more power, a more sensitive/selective receiver, better or higher antennas. Typical station characteristics follow:
Station Gain Factors Good Base SSB CB
Transmit power +10 dBW (12 Watts)
Transmitting antenna height gain 3 dB
Transmitting antenna gain dB
Receiving antenna height gain +3 dB
Receiving antenna gain 0 dB
Receiver sensitivity +149 dB (-149 dBW)
Total Station gain 65 dB
The ultimate goal of the radio system is to get a signal to the receiver that’s stronger than the background noise, so the signal can be heard. This is known as signal-to-noise ratio, and receiver sensitivity is usually stated as the lowest power level that will result in a given signal-to-noise ratio, typically 10 dB. Note that the receiver sensitivity is actually how much a signal can be reduced before it can t be heard (-149 dB) but it counts as a positive, as we have 149 dB in our station gain account that we can lose before we can’t hear a signal anymore.
The path loss is how the signal is reduced by the environment. Distance, air, mountains, water vapor are some of these factors. Distance alone reduces the signal at a rate of the square of the distance, e.g., a signal two miles away is one-quarter the strength of a signal one mile away, just because of the distance. Path loss varies (just a little bit) with the frequency used until one gets to microwaves, where path loss jumps significantly.
Under ordinary conditions between two stations on average terrain, path loss goes this way:
Frequency????????
10 Miles???? 25 Miles???? 50 Miles
27 Mhz (CB)????????
-135 dB???? -152 dB????????
-174 dB
144 Mhz (2M )????
-134 dB?????? -157 dB????????
-175 dB
For a good SSB CB radio, we have 165 dB of station gain, and we can communicate as long as path losses are less than this; on average terrain, this is somewhere between 25 and 50 miles. Note that if the antennas used are poor and low to the ground, this will change things considerably, as we’ll see in a few paragraphs.
In situations where the signal is bouncing around, such as short wave radio signals, loss includes both distance and the efficiency that the signal is reflected; when conditions are good, this reflection efficiency can be 100%, and only the distance matters. Likewise, if a satellite is used, the path loss is pretty much a result of just the distances between the ground stations and the satellite involved. Distance-only path losses run about -110 dB for 100 miles, or a typical low-earth orbit, and -151 dB for 22,500 miles, or geo-syncronous orbits. No place on earth is more than 12,500 from any other location, so the path loss for a perfectly reflected short wave signal is somewhere in-between.
Not that it’s done, but our 165 dB of station gain is quite a bit more than the 151 dB path loss of a geo-synchronous satellite, so it’s trivial for the satellite to hear a SSB CB or a 2-Meter Amateur radio. Indeed, several emergency systems depend on this: simple 1/2 watt emergency-radio beacons are detected with low-earth orbit satellites, and the newer 5-watt beacons are detected by geosyncronous weather satellites.
In the late 1980’s and early 1990’s the space shuttle carried the SAREX (Satellite Amateur Radio Experiment) program. Astronaut hams utilizing the 2 meter (144-148 Mhz) band communicated to thousands of earth bound hams, many utilizing only low power (0.5-5 watt) hand held radios.

b) Basic Radio Antennas

Antenna Effectiveness

Antennas can be measured by listening to a standard transmitter on the frequency of interest, and changing the antenna and noting the changes in the signal. Higher-end radios have meters that show relative signal strength, using numbers of 1 to 9 (S1…S5…S9) and then dB over S9; each S-unit is typically 6 dB. Using a calibrated receiver, we did measurements of a local weather station (near the amateur 2-meter band) to illustrate several antennas. We used the best antenna (which isn’t very good at all, actually) as a reference, and then compared several portable antennas:
Antenna Sig. Strength dB % Signal
Discone at 20 feet S9 0 dB 0 dB 00%
1/2 Wave Rod 6 S5 -24db 40%
Rubber duck, 6 S3 -36 dB 2.5%
Doing the same thing at CB frequencies:
Antenna Sig. Strength dB % Signal
Dipole at 20 feet S9 0 dB 100%
Rubber duck, 6 S0 -54 dB .0004%
Poor antennas wi
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Addendum:

SWR means Standing Wave Ratio….your antenna must be tuned for the frequencies that you are talking on. A 102 inch stainless steel antenna on your vehicle is probably the most easiest and most trouble free antenna there is. That measurement is in tune persay to the 11 meter bands like CB upper and lower sidebands, an swr is as important to an operator as the radio itself. Some are built into the radio. There is also a website that can answer alot of radio questions also, which is www.QRZ.com, very respectable web site……have any questions feel free to ask. I am considered a sidebander in your article and am presently studing for my ham license……bryan (nightowl488@yahoo.com)

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