SHTF Radio Basics

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I wrote this up for wirecutter, and he'll be posting it over at his place, but I wanted to see if I could post it in the "odt" formaI. I converted it to a "word doc" for him, as he was having trouble doing a copy-and-paste into his blog window.
Since I run Linux 99.9% of the time (OpenSUSE, to be specific), I use LibreOffice for all my office type documents, and this was a copy-and-paste of the odt file directly into the Blogger window. 
For those that don't know, LibreOffice is a "fork" of the OpenOffice project, which itself came from the StarOffice project way back in the early days of Linux.
While there are many excellent word processing and office-suite type programs available for Linux, LibreOffice/OpenOffice tend to be the "900 pound gorilla" since they're included in most Linux distributions.
Anyway.......
Kenny wanted something that covered the basics of why you might want to have a little radio in your "Git Kit", specifically something that covered more than just AM and FM, so I put this together over the course of a few weeks so he could post it. Seeing as he gets about a bazillion times the hits that I do, I agreed that it would be a good idea for him to post it so that more people could read it.
It's by no means the definitive word on "Emergency Radio" or "Survival Radio", and only covers receiving. One of these days I'll scribble something down about transmitting, as while it's nice to be able to listen, transmitting can be extremely important at times, too.


SHTFRadio Basics
If/when TSHTF, we'reall going to want to keep in touch with what's going on around us.This little article is about the first step in communicating byradio, and that's learning how to listen. Radio communication can runfrom communicating just within your local area, to covering all ofNorth America, to covering the entire world. It all depends on whatyou need, which determines what gear you need, and how you do it.There's no “magic” to it (well....maybe a little!), andmost anybody can learn how to use radio communications effectively.
I'm not going to teachyou how to design a radio or to repair one; this is just an intro tousing one. If you get really interested, the links provided at theend of this article will allow you to study and learn as much as youwant. Don't get scared offwhen you see new, unfamiliar words and terms. I put a glossary at theend so you can look up most of the new words and terms you'll belearning.Keep in mind that I'vetried to write this in simple language, for beginners. Yes, I've taken someliberties with some of the technical terms and descriptions, butthey're basically correct, so I don't want to hear “How wrong I am”from anybody with a lot of experience with radio. If you haveconstructive criticism, or find a glaring error or omission, I'llgladly welcome the feedback, but this 'aint a forum on eHam, so backoff a bit!And if you have somesuggestions, by all means submit them. If I think they fit in withthis article, I'll include them.
I've been a licensedAmateur Radio Operator since I was 12 years old, almost 50 years now.I didn't always have a transmitter with me in my travels, but Ialways had a General Coverage receiver with me, sothat's where we'll start, with General Coverage receivers.

GeneralCoverage Receivers
Broadly speaking, aGeneral Coverage receiver will pick up radio signals between 3MHz and30MHz. With today's modern radios, this also includes the AMbroadcast band, which covers 540kHz, to 1610kHz, and the FM broadcastband, 88MHz to 108MHz. Some radios will also include “Air Band”,108MHz to 136MHz which is what commercial and private aviation uses,and possibly the “Long Wave” band, which covers roughly 150kHz to500kHz. Commercial aviation frequencies are fun to listen to, but notall that important in a SHTF radio. Same with the “Long Wave”band which is mostly used for Non-Directional Beacons (“NDB”),and some types of weather broadcasting. Other, older radios may offer“TV Channel Audio”, but with the television stations goingdigital, this is pretty much useless these days. Same with radiosoffering a “Public Service” band or two. Very few Policeor Fire departments, especially in large metro areas, have simpleVHF/UHF radio systems these days. Almost all of them are on “Trunked”radio systems, and many are using digital audio (“APCO P25”)instead of analog audio. I'll cover other types of receivers, likescanners, in a separate article.Since we all prettymuch know about “AM and “FM”, I'll just briefly cover those,and then get to the frequency coverage (“Bands” or “Wavelengths”)that makes these little radios much more useful than just a typicalAM-FM portable radio.



AMRadio
Good Old AM (AmplitudeModulation) radio has been with us since the 1920's, over 90 yearsnow. It might be said (tongue firmly in cheek!) of radio that “InThe Beginning, There Was AM, And It Was Good”. These days, AM hasradically changed from the “Top 40” format I grew up with, tobeing mostly talk-radio, all-news, religious, and foreign language.And that's its strength. If you want local news, you get it duringthe day, out to several hundred miles depending on the power of thestation. If you want news from more distant areas, then listen atnight. There are “Clear Channel” AM stations in all the majorcities, and you can usually receive them coast-to-coast at night.Clear Channelstations, are by U.S. and International regulation, the only stationon that frequency 24 hours a day. There may be other low-poweredlocal stations, but when the sun goes down, the locals shut down.Clear Channel stations generally run 50,000 Watts of transmitterpower, although some of the Mexican stations run 150,000 Watts. Sincethey're the only station on that frequency, they'll be listenable allover North America at night. This allows them to be useful forgathering information from well outside your local area.

The current list ofClear Channel stations is below:
540 CBK Watrous, Saskatchewan540 CBT Grand Falls, Newfoundland and Labrador540 XEWA San Luis Potosí, San Luis Potosí640 CBN St. John's, Newfoundland and Labrador640 KFI Los Angeles, California650 WSM Nashville, Tennessee660 WFAN New York, New York670 WSCR Chicago, Illinois680 KNBR San Francisco, California690 CKGM[7] Montreal, Quebec690 XEWW Tijuana, Baja California700 WLW Cincinnati, Ohio710 KIRO Seattle, Washington710 WOR New York, New York720 WGN Chicago, Illinois730 CKAC Montreal, Quebec730 XEX Mexico City, D.F.740 CFZM[8] Toronto, Ontario750 WSB Atlanta, Georgia760 WJR Detroit, Michigan770 WABC New York, New York780 WBBM Chicago, Illinois800 XEROK Ciudad Juárez, Chihuahua810 KGO San Francisco, California810 WGY Schenectady, New York820 WBAP Fort Worth, Texas830 WCCO Minneapolis, Minnesota840 WHAS Louisville, Kentucky850 KOA Denver, Colorado850 XETQ Ixhuatlancillo, Veracruz860 CJBC Toronto, Ontario870 WWL New Orleans, Louisiana880 WCBS New York, New York890 WLS Chicago, Illinois900 XEW Mexico City, D.F.940 silent[9] Montreal, Quebec940 XEQ Mexico City, D.F.990 CBW Winnipeg, Manitoba990 CBY Corner Brook, Newfoundland and Labrador1000 KOMO Seattle, Washington1000 WMVP Chicago, Illinois1000 XEOY Mexico City, D.F.1010 CBR Calgary, Alberta1010 CFRB Toronto, Ontario1020 KDKA Pittsburgh, Pennsylvania1030 WBZ Boston, Massachusetts1040 WHO Des Moines, Iowa1050 XEG Monterrey, Nuevo León1060 KYW Philadelphia, Pennsylvania1060 XEEP Mexico City, D.F.1070 silent[10] Moncton, New Brunswick1070 KNX Los Angeles, California1080 WTIC Hartford, Connecticut1080 KRLD Dallas, Texas1090 KAAY Little Rock, Arkansas1090 WBAL Baltimore, Maryland1090 XEPRS Rancho del Mar, Rosarito, Baja California1100 WTAM Cleveland, Ohio1110 KFAB Omaha, Nebraska1110 WBT Charlotte, North Carolina1120 KMOX St. Louis, Missouri1130 CKWX Vancouver, British Columbia1130 KWKH Shreveport, Louisiana1130 WBBR New York, New York1140 WRVA Richmond, Virginia1140 XEMR Monterrey, Nuevo León1160 KSL Salt Lake City, Utah1170 KFAQ Tulsa, Oklahoma1170 WWVA Wheeling, West Virginia1180 WHAM Rochester, New York1190 KEX Portland, Oregon1190 XEWK Guadalajara, Jalisco1200 WOAI San Antonio, Texas1210 WPHT Philadelphia, Pennsylvania1220 XEB Mexico City, D.F.1500 KSTP Saint Paul, Minnesota1500 WFED Washington, D.C.1510 WLAC Nashville, Tennessee1520 KOKC Oklahoma City, Oklahoma1520 WWKB Buffalo, New York1530 KFBK Sacramento, California1530 WCKY Cincinnati, Ohio1540 KXEL Waterloo, Iowa1540 ZNS-1 Nassau, Bahamas1550 silent[11] Windsor, Ontario1550 XERUV Xalapa, Veracruz1560 KNZR[12] Bakersfield, California1560 WQEW New York, New York1570 XERF Ciudad Acuña, Coahuila1580 CKDO[13] Oshawa, Ontario

Alaskanclass A (former class I-N) stations Freq.
(kHz)Callsign City of license
640 KYUK Bethel650 KENI Anchorage660 KFAR Fairbanks670 KDLG Dillingham680 KBRW Barrow700 KBYR Anchorage720 KOTZ Kotzebue750 KFQD Anchorage770 KCHU Valdez780 KNOM Nome820 KCBF Fairbanks850 KICY Nome890 KBBI Homer1020 KOAN Eagle River1080 KUDO Anchorage1170 KJNP North Pole

FMRadio
FM (FrequencyModulation) radio was invented my Major Edwin H. Armstrong, one ofradio's true pioneers and visionaries. He received the patent forWide-Band FM on 26 December 1933, although widespread use of FMdidn't really catch on until the early 1950's. FM radio is virtuallyimmune to static and noise from natural sources, and most man-madeinterference. As a result, it's well suited to broadcasting HighFidelity music. It's also capable of excellent voice reproductionwith a smaller bandwidth than an AM signal, making it the choice forPublic Service agencies, like Police and Fire Departments, who NEEDclear, easy to understand voice on their radios.If there's a “problem”with FM radio stations, it's that their range isn't as great as AMstations. This has nothing to dowith the type of modulation (Amplitude vs Frequency), but rather thefrequency that the station broadcasts at. The 88-108MHz frequencyrange is pretty much limited to what's called “Line-of-Sight”,meaning that if you don't have a fairly clear path to the station, orit's over the horizon, you can't receive it.This means FM stationsare local in nature, and another good place to listen for localinformation.
In between the AMradio band that “hugs the ground” during daylight hours, called“Ground Wave”, and the FM/VHF/UHF bands that are limited to“Line-of-Sight” propagation, are the shortwave bands, and that'swhere we'll go next.


ShortWave Radio
Short Wave radio, alsocalled “HF” for High Frequency, covers the frequencies from 3MHzto 30MHz. Frequencies below 3MHz, along with the AM broadcast band,are called “Medium Wave”, or “Medium Frequency”. Many oldtube type radios had the bands labeled as such, calling them “LW”for Long Wave, “MW” for Medium Wave. And “SW” for Short Wave.Many of the better receivers had more than one Short Wave band, andthey'd label them “SW1”, “SW2”, and so forth.Besides being labeledwith frequencies, short wave bands are also referred to by theirwavelength, measured in meters. Thus, the 7MHz band is also calledthe “41 Meter” band, 11MHz to 12MHz is called the “25 Meter”band, and so on. The higher the frequency, the shorter thewavelength.The types ofmodulation you'll find on HF radio are pretty much limited (for ourdiscussion) to AM, and SSB. There are various digital modes used, butthat's beyond this article.
Why bother with ShortWave, and have to learn a bunch of “new” stuff? Well, when theSHTF, local news may very well be heavily controlled (i.e. censored),or even “blacked out”. Having an alternative source, from manymiles away, might actually be more useful. The BBC (BritishBroadcasting Corporation) was always good at providing unbiased newsfrom around the world, along with CBC/Radio-Canada, and so was theVOA (Voice of America), who specialized in beaming Pro-Americanprogramming to other parts of the world.Unfortunately, many ofthese radio services have been severely cut back in recent years,replaced by lower-cost streaming Internet “radio” services.While a “Short Wave”radio can receive many different frequencies, broadcasters usespecific frequencies agreed upon by international treaties, commonlycalled “Bands”.
The most commonly usedshortwave bands are below.
120m2300–2495 kHz tropic band90m 3200 – 3400 kHz tropic band75m 3900 – 4000 kHz shared with the North American Amateur Radio“80 meter” band60m 4750 – 5060 kHz tropic band49m 5900 – 6200 kHz 41m 7200 – 7600 kHz shared with the Amateur Radio “40 meter” band31m 9400 – 9900 kHz currently the most heavily-used band25m 11,600 - 12,200 kHz 22m 13,570 - 13,870 kHz substantially used only in Eurasia19m 15,100 - 15,800 kHz 16m 17,480 - 17,900 kHz 15m 18,900 - 19,020 kHz almost unused, could become a DRM band13m 21,450 - 21,850 kHz 11m 25,600 - 26,100 kHz may be used for local DRM broadcasting
Many, if not most,older radios that included shortwave coverage would add labels to thebands like “Mexico”, “London”, “Berlin”, indicating theapproximate place on the dial where broadcasts from those locationscould be found. They'd also label the bands “Evening”,“Afternoon”, “Morning”, or “All Day” to indicate whattime of day these stations could be heard. Why did they have thetime of day listed? Well, it has to do with what's called RadioPropagation. Propagation is the term used to describe how radiowaves travel through space. Propagation is a highly variable thing.How far shortwave signals will travel depends on what frequency theyare, the time of day, what season it is, and where we are in thecurrent sunspot cycle.I'll cover RadioPropagation in another article.


BuyingA SHTF/Emergency Radio
I could probably writean entire article on just this subject!I suppose the firstthing to ask yourself is “How much to I want to spend?”, and thesecond would be “How much radio do I need?”, along with “Whatdo I want to listen to?”. A decent, reliable, easy to use radiowill cost about $100, maybe less if you do your shopping carefully.Some of the more expensive radios are actually poorer performers thansome of the less expensive ones. Do you want to be able to listen toHams, or just International Broadcasters? Once you've decided on howmuch you want to pay, start looking at the reviews on eHam.net, under“Reviews/Categories/Receivers/General Coverage”. Keep in mindthat 99% of these reviews are written by Hams, and what they decidemakes a “Good” receiver is probably quite different than whatyou'll need. When reading reviews, I always like to look at the mostnegative reviews first. Some of them are hilarious, as in people whogripe about what color the radio is I also tend to steer awayfrom a review that only has a few entries, compared to a review thathas 20, 30, or more entries. Anybody can get a “dog” radio, justlike any other product, and a glowing review score of “5” fromone reviewer could also be a fluke.
As a general rule, Idon't care for those hand-crank/solar-cell “Emergency”flashlight/strobe/cellphone charger/radios you see advertisedeverywhere. If it's all you can afford, by all means get one, butmost of them are very limited in what they'll receive, and theirpretty marginal in their sensitivity. They're OK in metro areas wherethere's lots of stations, but they're pretty weak out in the boonies.
I've had several ofthem, and was really disappointed in their performance, but then Iguess I'm a little jaded about what a radio should be capable ofdoing.
I currently own aGrundig G3 “Globe Traveler”, and a TechSun PL-660, along withsome other, older radios. Both of these little guys are available forunder $100, fit in your coat pocket, and besides covering AM and FM,they also have “Air Band” coverage, and continuous tuning from150 kHz to 30 MHz. They also both have a TON of memories to storefavorite frequencies in, a Synchronous Detector for helping toeliminate what's called “Selective Fading”, and a BFO (“BeatFrequency Oscillator”) which allows them to receive Single Sideband(“SSB”) signals from Amateur Radio operators, and various utilitystations in the MW and SW bands.They both run on 4“AA” batteries, and will charge NiMh batteries with theirincluded AC adapter/charger, or run just fine on alkaline or Lithiumbatteries.These things areabsolute marvels of Engineering. They receive more things, and dothem better, than my first Amateur Radio receiver.For larger, “base”or “table top” type receivers your options for buying new arequite a bit more limited, simply because most manufacturers stoppedmaking medium range receivers. Currently, Icom sells the IC-R75, avery good little radio, and Alinco sells the DX-R8T, another decentradio. Most of the other radios available are eithercomputer-controlled, or very high-end models that start at $800, andgo up from there.I won't go into buyingolder radios, or tube-type radios as that's beyond the scope of thisintroduction. If you're really into vacuum tube gear, you probablyalready have some, and are already ahead of the curve on this.For good reviews onthe currently available, small, SHTF radios, check out the reviewspages on eHam.net under “Reviews Categories>Receivers:GeneralCoverage”.




SomeBasic Tips Not Otherwise Covered.......
If you're notgoing to be using the radio for a while, like when you store it,
====>TAKE THE DAMN BATTERIES OUT! <====
Oneof the most depressing thingsis to get your SHTF or “emergency” radio out, and not onlyfinding dead batteriesin it, but seeing all the glop those dead batteries have leaked allover the battery compartment, corroding everything metal withinsight. Yes, you can clean them up if they're not too badly corroded,but why take the chance in the first place?Your radio will thankyou. I just checked the batteries in all of our remote controls, andwas ready to kick myself in the rear end.....ALL of them had gonedead and leaked!Looks like I'll bespending some time cleaning up a whole lot of little battery contactsin the near future.
BTW...”TARN-X”silver cleaner works wonders at getting minor batterycorrosion off the contacts. Brush the contacts with a small brush toget the big chunks off, and then apply the TARN-X sparinglywith a cotton swab. You'll see any residue foam up, and the greencorrosion will disappear. Flush any remaining residue away with aswab and some clean water. I've done this several times on equipmentthat had dead batteries left in it, and it really cleans up thecontacts. If the contacts are really bad and have to be replaced, youmight be able to find replacement contacts at Mouser, DigiKeyor Keystone Electronics.
Batteries- Tryand buy a radio that uses a “common” battery size as the rest ofyour SHTF gear. If your radio is the only piece of gear you havethat uses “C” or “D” batteries, that's one extra battery sizeyou'll have to stockpile. Think of it like you do ammunitioncalibers, and try to 'standardize' one more thing.
NiCad and NiMHbatteries are good in that they can be recharged, BUT they only putout 1.2 Volts per cell, while alkaline and lithium batteries put out1.5 Volts per cell. If your radio takes four batteries, the NiCad andNiMH cells will only have 4.8 Volts instead of 6 Volts.Will this “hurt”the radio? No, but you'll probably see the “Low Battery” displayall the time, and if the device has a low battery shutoff, thebatteries might not power the device very long before it shuts offeven though the batteries have plenty of juice left in them!Lithium batteries havevery long shelf life, and are capable of putting out a burst of highcurrent, which is nice for things like flash units, orwalkie-talkies, but cost considerably more than alkalines.
And BE AWAREthat Nicad and NiMh batteries require different charging methods!Most of the inexpensive chargers for sale will either have a switchto select which type of battery is being charged, or will auto-detectthe battery type. Mixing battery types in any device is a BIG no-no,and can result in damage to the device, or in extreme cases, a fire.
If your SHTF radio hasa connector for “External Power”, see if you can get a cable or“Cigar Plug/Cigarette Lighter Adapter” that will let you power itfrom 12 Volts DC.
Some people will askabout how to protect a solid-state (Transistorized) radio from an EMPevent. I keep both my little Grundig G3 radio, and my Elecraft K2 HFtransceiver in metal ammo cans. The Grundig fits into a small 30 calcan, along with some extra AA batteries, and the AC power supply. TheK2 is a bigger radio, so I store that one in a larger 20mm can. Ifyou're really paranoid about EMP, then seal the edges of the canswith some aluminum tape (NOT duct tape), making sure that all theseams are covered. I also keep a power supply for the K2 in aseparate can, although if we ever have an EMP event, the power gridwill most likely go down, so the power supply might very well beuseless.And I always toss acouple of desiccant bags in the cans before I close them.
If you're really thatconcerned about having some radio gear survive and EMP, then look into getting some older gear that uses vacuum tubes. There are somevacuum tube General Coverage receivers that run on batteries, but thereplacement battery packs haven't been available for DECADES.The Zenith Trans-Oceanic is one, Hallicrafters made a few differentmodels, and I'm sure there are others. You'll have to cobble togetheryour own battery packs, and that's WAY beyond this article,and you'll have to pay “Collector” prices for these sets.
Antennas- Mostof the newer radios have acceptable sensitivity with the built-inwhip antenna. If you think you need more, you can string someinsulated wire up, and either wrap a few turns around the whip (AFTERyou stripped the insulation off!), or use a clip-lead to attach it tothe whip. A lot of the new little radios have a jack to connect anexternal antenna to, but be careful! Some radios will overload withan external antenna, especially if you live near a high-power radiostation. My little Grundig G3 has a “Local/DX” switch that addssome attenuation to the antenna circuit, making it less sensitive,and cutting down on overloading when used with an external antenna.The rule-of-thumb forshort wave antennas is get it as high as you can, and make it about50' long. Going much over 50' will pick up more noise than signal, atleast in an urban area. Just be careful that the antenna is wellclear of any power lines, and that if it breaks, the pieces of itwon't fall on any power lines.Don't worry aboutgetting the antenna length matched to the wavelength you want toreceive. This is more important for transmitting than receiving, andsince most of the portable radios we're concerned with are made touse the somewhat less than optimum whip antenna that's built in tothem, adding some extra wire that's up and in the clear is theimportant thing.
Headphones- Ahyes, a good set of 'cans' for those times when you don't want todisturb others, or don't want anybody else to hear what you'relistening to, or that you're listening at all. I prefer the'over-the-ear' type that cover the entire ear, and seal outbackground noise. There might be times when 'ear buds' areappropriate, but for digging out really weak signals (I'm talking“ESP weak”!), NOTHING beats a good set of headphones. Watch outfor the “open back” type that seal to your head, but allow soundto radiate out the back of the earpieces. And you don't need$600 “audophile” quality 'phones. Human speech covers roughly20Hz to 20kHz, and unless you're young, or have exceptionally goodhearing, you probably can't hear 20kHz anyway. Radio Shack has somedecent ones for under $50, as does Best Buy.We're looking for“Communications Quality” audio here, NOT something to listen to a$3000 stereo system with!

OtherResources
Monitoring TimesMagazine- One of the best out there. Covers everything in thisarticle, along with beginner to expert articles and columns. HIGHLYrecommended.http://www.monitoringtimes.com/
Nuts & Volts-A very interesting magazine. Covers a wide range of topics, and hasabsolutely KILLER ads for the hobbyist/experimenter.http://www.nutsvolts.com/
PopularCommunications Magazine- I haven't read this in years, so I can'tvouch for it. Some people love it, some hate it.http://www.popular-communications.com/
Dxing.com- Homeof the “Modern Shortwave Receiver Survey”. Also has ratings forolder radios.http://www.dxing.com/rx.htm
QST- Theofficial magazine of the American Radio Relay League (AARL). This isgeared towards Amateur Radio (“HAM” Radio), but has wide varietyof articles. Considered one of the premiere radio magazines in theworld.http://www.arrl.org/
eHam.netwebsite- Has product reviews and forums geared mostly towards HamRadio, but has forums for Shortwave listeners.http://www.eham.net/
Radio Referencewebsite- For scanner users, this is a MUST website! They havecurrent, ACCURATE databases of all non-military radio frequencyassignments in the U.S., and excellent forums. Several of theapplications used to program modern “Do Everything” scanners arecapable of extracting the data from the Radio Reference website, andwill send it directly to your scanner, saving HOURS of time enteringfrequencies by hand.If you have a questionabout scanners, you'll probably find the answer here.http://www.radioreference.com/
Phil's Old Radios-A marvelous site to learn about restoring old radios, and admire hispatience and craftsmanship.http://antiqueradio.org
RadioIntelwebsite- A nice site with tons of info and links to other websites.http://www.radiointel.com/ref.htm
Ham Radio Outlet-Sells new and some used radios. Also sells antennas and other neatstuff.http://hamradio.com/
Amateur ElectronicSupply- One of the oldest places around for buying new and usedgear.http://www.aesham.com/
Universal Radio-Another seller of new and good quality used radio equipment, books,and accessories,http://www.universal-radio.com/index.html

Glossary
AC: AlternatingCurrent. A current which changes polarity (or direction if that makesit easier for you to understand) with respect to time. The voltageout of your wall socket is A.C.
AM: AmplitudeModulation. A form of modulation in which the information applied tothe carrier wave causes it to change in amplitude. An AM radio signalconsists of a Carrier Wave, and two Sidebands, one above, and onebelow the carrier wave.
Amateur Radio:A NON commercial radio service used by licensed individuals formessage exchange, experimentation, self-training, and emergencycommunications.
Antenna: Adevice for capturing radio signals from the air. Can be a length ofwire, a “whip”, a “discone”, or a directional antenna, likethe old TV antennas we all used to have. Generally speaking, antennasare most efficient when their physical length corresponds to theelectrical wavelength of the signal being received.
BFO, or BeatFrequency Oscillator: A circuit in a radio receiver that allowsit to receive Single Side Band radio signals, and properly demodulatethem.
Carrier Wave: Aradio signal without any information applied to it. Sometimes justcalled a “carrier”, or “dead carrier”.
Current: The“flow” of electricity through a circuit, measured in Amperes.Think of it just like the flow of water in a hose.
DC: DirectCurrent. A current which does not change polarity, or direction. Yourcar battery (really, ANY battery) is a source of Direct Current.
Demodulation:The process of recovering the information that was put on to a radiowave.
DRM: DigitalRadio Mondiale. A digital audio broadcasting format used in certainshortwave bands. It requires special equipment to receive, but hasexcellent (“FM Quality”) audio quality. Most receivers can beeasily modified to allow a PC sound card to decode the audio.
FM: FrequencyModulation. A form of modulation in which the information applied tothe carrier wave causes its frequency to change.
Frequency: Thenumber of times per second an electromagnetic wave changes polarity,expressed in “Hertz”, abbreviated “Hz”. One thousand Hertz isone kiloHertz, kHz, and one million Hertz is one MegaHertz, MHz.Frequency and wavelength are inversely related. The lower thefrequency, the longer the wavelength, and the higher the frequency,the shorter the wavelength. The AC power out of your wall socketchanges polarity 60 times per second, so it's called “60 Hz A.C.”
Ground Wave:Radio waves that primarily travel along the surface of the Earth.
Ionosphere: Aregion of the upper atmosphere, consisting of charged (“ionized”)particles starting at approximately 50 miles above the surface of theEarth, and extending out to approximately 375 miles. The particlesare ionized by energy from the Sun. The ionosphere is divided intolayers, with the “D” layer being the lowest, and the “F”layer being the highest. The heights of the layers, their thickness,and their density, determine which radio frequencies are reflectedback to Earth, and which are absorbed. The layers all change with thetime of day, the seasons, and the sunspot cycle.
Line-of-Sight:A term used to describe the “path” that a radio signal follows.This is determined mostly by the frequency used. Lower frequencies,like those used for AM radio, tend follow the nap of the Earth betterthan the higher frequency signals like those used for FM andTelevision. An AM radio station can be heard well past the“Line-of-Sight” to it, where you need a “clear shot” to a TVor FM station to hear it well.
Modulation: Theprocess of putting information (voice, music, pictures, data) on to aradio wave. The two most common forms are AM, where the amplitude isvaried, and FM, where the frequency is varied.
NiCad: Shortfor “Nickel Cadmium”, and early type of rechargeable battery.Still pretty good for uses that require a burst of high current, likefor transmitting. They suffer from the “Memory Effect” whichmeans if you don't FULLY run them down before you recharge them,they'll 'remember' they still have a little charge in them, and won'tcharge back to to a usable 100%. Most modern NiCads, and modernchargers, can overcome this, but be aware of it.
NiMH: Short for“Nickel Metal Hydride”, and improved type of rechargeablebattery, similar to a NiCad, but using a different metallic compoundin place of Cadmium. Much more forgiving then NiCads oncharging/discharging, and pack more useable power in the same sizethan NiCads.
Radio: The artand science of using electromagnetic radiation to communicate or exchange information over long distances.
Receiver: Adevice that converts radio signals into a usable form. The outputcan be video, as in a TV set, audio, as in a radio, or data, as in aradio modem.
Selective Fading:Also called Frequency Selective Fading. A type of signal distortionwhere one of the sidebands of an AM radio transmission becomesattenuated more than the other sideband.
Single Side Band,Single Sideband, or SSB: A special type of AM radio signal thateliminates one of the sidebands, and the carrier wave. This allowsapproximately four times the transmitter output power for a givensize of amplifier in the radio.
Sky Wave: Radiowaves that do not primarily travel along the surface of the Earth,but go into space, to be reflected back by the ionosphere. Dependingon the frequency, the signal may be reflected back to Earth a fewhundred miles away, or many thousands.
SynchronousDetector: A special type ofdemodulation circuit used to minimize the effects of selectivefading.
Trunked RadioSystem: A type of radio “Party Line” where all radios receivea “Control Channel” along with the regular channels programmed into them. When one radio calls another radio, the Control Channeltells both radios what frequency is clear to use, and they both tuneto it automatically. This allows multiple groups, like Police, Fire,and Civilian users to share the same radio system. It can allow thePolice and Fire to inter-communicate, while keeping the Civilians“locked out” of those channels. If you hear about big citieshaving major problems with their radio systems, it's a TrunkedSystem!
Voltage: The“pressure” that drives the electricity through a circuit,measured in Volts. Think of it as the pressure of the water in ahose.
Wavelength, orWave Length: The length, generally stated in Meters, of aradio wave. A “40 Meter” (7 MHz) radio wave is about 134 feetlong, and a “10 Meter” (30 MHz) radio wave is about 31 feet long.
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