i'll take a shot at this, and provide some links as well since my fingers would fall off before i could type everything you might want to know.

the usable-for-communications electromagnetic spectrum spans a frequency range from about 100KHz to 100GHz. (aside, only a portion of that is usable by inexpensive equipment). in the USA, the federal communications commission (FCC) is responsible for administering the spectrum for US users; however, the FCC works closely on this with international bodies, for reasons which will soon become clear. the "administering" that the FCC performs includes dictating what frequency bands are to be used for what purposes, and also specifying operational requirements for those bands (e.g. TX power output, ERP, modulation type, etc).

since examples are worth thousands of words, i'll provide a few. 1) the FCC has decided that broadcast FM stations are to exist in the 88MHz to 108MHz range. there are certainly power limits however i've no idea at hand what they are. 2) the FCC has decided that CB exists at around 27MHz, and that the maximum TX power output is 4W. 3) the FCC has decided that FRS exists around 462/467MHz, with a maximum ERP specified. and for the last example, 4) ham (amateur radio) has a number of bands allocated, each with associated limitations on power/modulation etc. i could go on and on with cell phones, marine radios, garage door openers, keyfobs, microwave towers, etc etc etc. basically, if the device is what is referred to by the FCC as an "intentional radiator", they have an assigned slot (band) for it and constraints on it's operation.

why the constraints? well, one reason is for your physiological protection. high RF power can cause burns, blindness, and other problems. (the "invention" of the microwave oven was an accident -- technicians working on early radar antennas were developing burns when the units were powered). another reason for the constraints is public safety. the last thing a 747 pilot on emergency approach into Kennedy airport needs is crosstalk with taxi dispatchers in NYC. hence the wide berth the FCC gives around police, fire, and EMS frequencies.

now then, we see that the FCC regulates intentional radiator use by dividing the frequency spectrum into bands, and then sets characteristics for each of those bands that users must obey by.

a common question is, "is one frequency band 'better' than another"? the answer is "sometimes". for certain applications (more on this in a moment), a given frequency band may provide better range, fidelity, immunity to interference, and so forth. these factors, and others, that make a frequency usable for a given application were taken into consideration when the spectrum was allocated.

it is important to note here that transmitter power output is one of many, many factors that influence the range at which you can communicate over a given transmission path. while important, transmitter power output plays only one role in a multi-faceted problem. antenna gain, antenna polarization, modulation type, receiver sensitivity, background noise level, path loss, and a dozen other issues factor into the equation. show me a well designed 2W transmitter and i will show you a way to communicate ~6.5 billion miles. NASA does this every day with their Voyager 1 & 2 probes -- they are now twice as far away as Pluto.

you wanted to talk about ham radio, so now that you understand a little of the background we can move on.

to simplify things, amateur radio communication can be thought of in two segments: HF and VHF/UHF.

first, i hate to break this to you, but THE EARTH IS ROUND. no, i'm not kidding -- it really is spherical despite what they told you in school or at church. ok, now that you are past that, you should visualize in your head that radio waves travel in a straight line. since the earth curves, it is not possible to talk over distances of over about 20 miles without "help". this "help" can come in a multitude of ways, and is somewhat dependent on the height of the transmitter and receiver, the gain of their respective antennae, the frequency of transmission, the weather and other atmospheric conditions, the sun cycle, hams around you erecting things called repeaters, and a few dozen other things. nevertheless, the key point here is that the further you are away from each other, the more likely it is that the curvature of the earth is going to be the limiting factor. always remember that without "help", radio communications are "line of sight".

HF, or high frequency (roughly defined as everything below about 30MHz [10 meters wavelength]) signals can bounce off of a charged belt (called the ionosphere) which completely envelopes the earth. HF thus can communicate over long distances by using one or more "bounces" -- you may have heard the CB term "skip". with just a few dozen watts, and a proper antenna, it's possible for you to talk (or more likely communicate using morse) with a station 2000 miles away. interestingly, it is sometimes difficult to talk to nearby stations that are "under the skip", that is they are too close to you to hear the reflected wave. one primary disadvantage of HF communications is that the antenna has to be physically long. nevertheless, HF can be a valuable asset in emergency commications -- like it was during hurricane katrina when everything else was tits up. in general, when you think of HF you should think of long distance comms. with some exceptions, most HF rigs are designed for desktop use and the supporting equipment (power supplies, antenna tuner, etc) is heavy and not so portable. but there is a class of mobile and low power HF rigs which allow you to talk over great distances with just a few pounds of equipment.

aside: there is an entire "sub-culture" within ham radio of people dedicated to QRP, or long distance very low power communications. hundreds or thousands of miles on 5W, 1W, or even 0.5W is their goal. antenna selection and a good idea of what the ionosphere is doing are prerequisites.

VHF/UHF, or very/ultra high frequency (roughly defined as everything above about 50MHz [6 meters wavelength]) signals do not bounce off of the ionosphere. hence, VHF/UHF is pretty much "line of sight" except for some atmospheric effects which occasionally allow communications to take place out to a few hundred miles. these effects can not be "scheduled" though, mother nature has her own clock. in other words you can not depend on these phenomena for reliable communications. when you think of VHF/UHF you should think of short distance comms. amateur radios in the 6M (50MHz), 2M, (146MHz), 1.25M (220MHz), and 70cm (440MHz) bands are examples of VHF/UHF equipment. hand held radios in these bands are knowns as "HT's", or handy talkies. of course there are mobile and base versions as well that sport more output power or additional capabilities.

continuing on, FRS (UHF, ~462/467MHZ) and GMRS (UHF, same) are examples of inexpensive general purpose you-don't-need-a-ham-license radios. most commercial radios (tow trucks, florists, plumbers, Amtrak, mall ninjas, etc) operate in the 150MHz VHF band. and until somewhat recently, most public safety (police, fire, first aid) were in the 150MHz and 450MHz bands as well. however, within the last 5 years many have migrated to the 900MHz band using what are called trunked radio systems. long story there but trunking allows a lot of flexibility for the system. you'll note that VHF/UHF radios are cheap, small, have short antennas, and long battery life. moreover, amateur VHF/UHF radios double as scanners for the public service and other frequencies as well. the most popular VHF/UHF "band" is 2M, or about 146MHz. there is a reason for this... read on.

as noted above, the primary limitation of VHF/UHF is the short range imposed by the curvature of the earth combined with the fact that VHF/UHF signals do not bounce off of the ionosphere (in case you were wondering, they pass right through it). of course it helps greatly with VHF/UHF to be up as high as possible, as this gives more "line of sight" distance -- the same way you can see much farther when atop a tall building. but that's not always practical. e.g., i live right at sea level -- no kidding. how can i, the low lying ham, communicate with any distance using VHF or UHF? am i stuck trying to use HF for comms more than a few miles?

enter the "repeater". simply put, a repeater is an unattended radio advantageously located on a hill or with the antenna high up on a tower. the purpose of the repeater is to retransmit your signal in real time. it does this by listening on one frequency, called the input, and simultaneously transmitting the input audio on a second frequency, called the output. accordingly, my radio would be set to transmit on the repeater's input frequency, and listen on the repeater's output frequency. (the difference is known as the "offset".) all that is required from a radio implementation standpoint is a little bit of frequency agility -- when you press the transmit button, your radio tunes it's transmitter to the required new frequency. when you unkey, it changes back. all this happens in milliseconds and without your involvement save for some initial settings. the beauty of this set up is that with a low power HT (typ, 0.5W to 5W) you can talk for perhaps hundreds of miles! the repeater provides the "help" for VHF and UHF, just like the ionosphere provided the "help" for HF.

ham radio clubs set up, operate, and maintain repeaters. there are likely several repeaters reachable from where ever you are reading this from. from my home i can reach about 8 repeaters, of course i do live near a metro area with a high population density. note that there are published books of public amateur repeaters, which denote their location and characteristics (e.g., output frequency and offset). the reason that 2M/146MHz radios are so popular and inexpensive is simply due to the fact that there are more repeaters on 2M than any other frequency. don't think that repeater technology is something specific to hams -- it's not. police departments and the like use repeaters for the same reasons that hams do. in fact, this created a big problem on sept 11, 2001 as several of the NYPD and FDNY repeaters were located atop the WTC.

the disadvantage of repeaters is simple: in order for the repeater to work, you need power and the antenna has to be upright. these are not likely conditions in areas overcome by, for example, a category 4 or 5 hurricane. while tons of lead acid batteries may delay the inevitable, there is a finite amount of no-AC-power operation time for any repeater unless expensive measures have been taken (e.g. a diesel genset and good sized fuel tank, as you would find mounted behind a police station). nevertheless, hams are resourceful people and generally fixing the repeaters is an immediate priority in diaster areas. moreover, all the equipment necessary for a repeater can be carried in the back of a Tacoma, with room to spare. so if a makeshift antenna can be erected on the mountainside, a substitute repeater can be up and running in a few hours to replace the one crushed by the flying oak tree.

one way to look at a ham repeater is as an analog of a cell site. having many cell sites make it possible for your low power cellphone to communicate anywhere the global phone network reaches. similarly, hams link repeaters using point-to-point RF, the phone network, or these days using the internet. all of these methods allow greater "reach" from your low power HT. with the exception of point-to-point RF, the other methods require public infrastructure that may or may not be available when the SHTF.

speaking of the 'net, i've discussed above mainly voice communications. hwoever, hams also have packet radio technology at their disposal. so email and traffic nets can be set up without relying on the Internet -- instead of wire and fiber, RF is substituted. think of it as a wireless LAN, capable being accessed by anyone in an area of a few dozen miles in diameter.

in short, ham radio is not a singular thing; it is a wide, expansive hobby with many aspects to it -- you simply choose the parts that you enjoy. it's no different than with trucks, some like lifting and then offroading their Tacos and others make lowrider bling-bling trucks out of them. similarly, hams do HF, VHF, UHF, microwave, CW, packet, APRS, DXCC, contesting, SSTV, fox hunting, RACES/ARES(*), and so on and so forth.

ps:
useful/interesting sites:
http://www.qrz.com/i/howtoham.html <<<***
http://www.qrz.com/p/testing.pl <<< ***

http://wireless.fcc.gov/services/amateur/
http://wireless.fcc.gov/services/am...sing/index.html

http://www.arrl.org
http://www.qrz.com
http://www.eham.net
http://www.ew.usna.edu/~bruninga/aprs.html

(*) RACES/ARES
http://www.races.net/
http://www.races.net/links.html
http://www.ares.org/

for mobile to mobile communications, such as would occur when off-roading, you can use "simplex" (direct) communcations in the VHF 2 meter band. no repeater needed, you are talking directly to each other. a common frequency for initiating this is 146.52MHz, the national simplex calling frequency. once you have contact made you can move up a few hundred kilohertz and use any of the designated simplex frequencies to carry on.

using an HT (handie-talkie) running 1 to 5W, you can expect up to about 10 miles of range. it depends highly on the terrain (flatter better) and what sort of antenna you have connected.

using a mobile rig running about 50W into a roof or bracket mounted antenna will net you anywhere from 10-50 miles of range. generally the curvature of the earth will cause problems, so it is better to be up on a hill of you are trying to reach out past 20 miles or so.

a 2M-only HT is about $130-150.
a 2M-only mobile is about $140-180.

many HT's and mobiles are "dual-band" in that they operate on both 2M (~146MHz) and 70cm (~440MHz). this gives more flexibility for operating. note however there are far far far more repeaters on 2M, so there is no significant downside to getting a 2M-only rig.

popular HTs and mobiles come from the Big Three: Icom, Yaesu, and Kenwood all make fine radios with marginal differences. mostly it's individual preference, unless one feature is striking you just right.

the Icom V8000 is a very nice 2M-only 75W mobile rig. i happen to own two of them. as for HT's, there are also many types; i own a Yaesu VX6R -- tri-band (incls 220MHz) super small and completely waterproof. i also own an Icom 24AT, a rugged dual-bander which i have had since 1991. it has never let me down and i've worked through a few Nor'Easters and hurricanes with it.

http://www.yaesu.com/
http://www.icomamerica.com/
http://www.kenwood.net/

one thing i just realized, i never really explained what modulation is. simply put modulation describes the technique used to put the audio input to the radio (i.e. your voice) onto the RF carrier. there are many ways to do this, each with advantages and disadvantages. moreover, not only can it be done in the analog domain, but it can be done digitally as well. i'll only discuss the former as there are very few consumer digital radios to be had.

the most common analog modes are CW (continuous wave), AM (amplitude modulation), FM (frequency modulation), and SSB (single sideband [suppressed carrier]) modulation.

CW is used for morse code and is very efficient for long range comms. CW is not really a modulation method per se, but nevertheless we treat it as such.

AM, as you may be aware, is used for broadcast radio stations (hence the "AM band" name) and for shortwave stations (like Voice of America and Radio Free Europe). because of the low fidelity of AM, and it's susceptability to interference, AM radio has been relegated mainly to talk and newscasts. note that CB uses AM as well.

FM, as you are also aware, is used for broadcast radio stations and also is the mainstay for VHF/UHF communications. above 50MHz (6M), 99% of ham, all of FRS/GMRS, marine, and all public service/safety use frequency modulation. FM provides far greater fidelity (accuracy of the receiving radio's output to the transmitting radio's input) than any other modulation type. therefore, FM is very useful for music transmission. and similarly, FM makes 2 way radio communications crystal clear. most folks who have only used a CB are incredulous at what a 2M ham rig sounds like. the difference is due to the use of FM -- and not power or anything else.

SSB is the most complicated of all of the noted modulation techniques. simply put, SSB is an adaptation of AM with a little math (a Hilbert transform) thrown in. the result is a VERY efficient way to transmit speech over long distances. SSB is the primary modulation method used by hams when operating below 50MHz (6M). there are actually two types of SSB (USB and LSB) and in order to communicate both parties need to use the same type. nevertheless, SSB is one reason you can talk a few thousand miles on a couple of watts.

since someone is bound to ask... what does 2M mean? why is it seemingly used interchangably with 146MHz?

hams simultaneously use one of two terms to describe the band they are discussing: frequency or wavelength. the two are related by a constant known as C, the speed of light. it turns out that after you crunch the numbers, you can easily convert between the two terms using the following rule of thumb...

300/freq in MHz = wavelength in meters
or the same rule but turned around,
300/wavelength in meters = freq in MHz

hence:
300/146MHz ~= 2 meters

and now you see why 146MHz and 2M are used interchangably.

simlarly, some wavelength to frequency conversions for other popular HF and VHF/UHF ham bands...
40M --> 300/40 ~=7.5MHz
20M --> 300/20 ~= 15MHz
10M --> 300/10 ~= 30MHz
6M --> 300/6 ~= 50MHz
1.25M --> 300/1.25 ~= 220MHz
70cm --> 300/0.70 ~=440MHz

other cool/random radio-related links...

wiki stuff of interest:
http://en.wikipedia.org/wiki/Amateur_radio

http://en.wikipedia.org/wiki/High_frequency
http://en.wikipedia.org/wiki/20_meters

http://en.wikipedia.org/wiki/Very_high_frequency
http://en.wikipedia.org/wiki/2_meters

ham radio bandplan:
http://www.arrl.org/FandES/field/re...s/bandplan.html

bajataco's setup:
http://www.bajataco.com/electronics/comm-nav.html

pics of my disaster/ready kit; everything needed for 2 days in one waterproof box -- incl a 2M HT and roll up J-pole antenna:
http://losdos.dyndns.org:8080/public/bugoutbox/

i had some queries via PM and figured it would be useful to the rest of the world to copy them here...

jim aka the wrooster

Quote:
I think one major concept that just isn't clicking with me is how HF exists at 30Mhz and below, VHF/UHF exists at 50Mhz and above, yet CB radios work off of 27 MHz.

yes, CB exists within the "HF" frequency range (~1MHz to 30MHz), as does amateur radio. CB is allocated, as you already know, a band right near 27MHz (~26.965 to ~27.405), and the amateur 10meter band is just slightly higher at around 28.0 - 29.7 MHz. all things being equal, CB and ham would have approximately the same range since they are both affected the same way by the ionosphere. but clearly there is something else different, something that gives one an advantage over the other... keep reading...

Quote:
This is difficult enough for me to explain, but I'm hoping you'll realize what I'm getting at. How does a CB work off of 27MHz, when an HF radio uses nearly the same frequency, but is able to communicate exponentially farther? Is this because radio frequency has really no correlation with power, and it just so happens that at 10M, a frequency has the ability to reach and skip off the ionosphere?

power is one aspect of range, an important one -- but not the only one. as i discussed in the third or fourth post in my "ham 101" thread, the way the audio is modulated onto the RF carrier is extremely influential on how easy or difficult it is to recover the audio at the other end. AM is one of the worst possible ways to transmit voice, and that's the type of modulation CB uses. AM, combined with only 4 watts output, is just not going to make it as far as a superior modulation method combined with more power. in contrast with AM, SSB is much much much (i can't emphasize this enough!) more efficient in terms of using the available power to greatest effect. ergo, SSB, combined with the higher power available on ham rigs, allows for far greater communication distance at very nearly the same frequency as CB. so as you can see, it's not just about power.

(i would also like to point out here that the receiver section on a typical ham radio is miles ahead of the receiver section on a typical CB radio. you need to cut some corners in order to make a CB that sells for $50. a ham rig, on the other hand, is at a price point that allows for better components (oscillators, filters etc) and additional circuitry (especially DSP [digital signal processing]). so if you look at the entire communications path from strictly a power perspective, there are two factors: how powerful the transmitter is and how sensitive the receiver is. hence, you can improve range by increasing transmitter power and/or increasing receiver sensitivity. if you do both, you get a lot more range. this is the case with the higher power output and excellent receivers on ham radios. and we haven't even plugged in the benefit of using SSB modulation yet! remember, IT'S NOT JUST ABOUT POWER. lots of hams use less than 10W to talk around the world. the art here is understanding propogation conditions, using the right modulation mode, driving a proper antenna, and having a good quiet (low noise floor) receiver.

Quote:
I guess I just don't understand how such a low frequency would have that ability (10M), and a 2M wouldn't.

the ionosphere does not reflect frequencies above about 30MHz. above that, they just keep on going, off towards Mars. so, unless under very infrequent conditions, 2M (~146MHz) can not be used for long distance comms as it will not bounce back down to earth. (aside: there is a aspect of ham radio which consists of bouncing 2M signals off of the moon. this is called "EME", or "earth-moon-earth" communications. in this manner you can use 2M/144MHz to talk to the other side of the earth. warning: you need a lot of power and a big ass beam antenna to pull this off. moreover, the antenna must be able to track the moon as it crosses the sky, guided either by optical means or by using ephemeris data)

Quote:
I think that, after reading your "101" post, a mobile 2M radio would best suit my needs. I noticed you have a mobile 2M in your truck. Do you use the 146.52MHz much like you would channel 19, to scan for others? Are there a lot of drivers and truckers that use this also?

you can use the "national simplex frequency", 146.52 sort of like CB channel 19. my 2M radio is set up to scan it in one of the memory banks. often i will hear someone call on it, and answer back. sometimes they are just trying a new radio out, other times they are from out of town and looking for popular local repeater frequencies, and other times it's just to say "hi" and so forth. generally you can "meet up" on .52 and then move off slightly to allow others to use the calling frequency. or you can simply chat on .52, allowing a little extra time between alternating transmissions -- then if someone wants in, they will interject with just their callsign. at that point you will "recognize them" by repeating their call back and saying "go ahead" (in effect, handing them the baton for the moment), and thus allowing them the opportunity to either join your conversation or to call for another station that they may have had a prearranged hook-up time for. this is actually all very simple and the first time you hear it happen live it will be very clear to you how to do it yourself in the future. the operating procedures in place on ham radio make it a much more enjoyable environment for everyone.

Quote:
Now, as far as licenses go. I know I should just go ahead and get the tech license, but I want to understand this first. The tech license states that it is for communicating over 50MHz.

that is correct. pass the Technician class written test (no morse code test required) and will you have full operating privileges over 50MHz (6 meters). your FCC callsign will arrive in the mail in about a week, and you are a ham. borrow/buy a 2M radio, and you can chat with the nearby hams on 146.52 and of course use the local repeaters as well. for any new ham i would suggest listening to conversations (called "QSO's") on the repeaters for a bit to get the operating procedure down. again, it's VERY simple but you should listen first to see how it's done before jumping in with both feet.

Quote:
Does this mean you don't need a license to operate an HF radio?

you absolutely need a license to operate HF, and the catch is that (currently) you need to pass a 5 words-per-minute morse code listening test (in addition to a written test) in order to get a license to operate HF. this morse code requirement is actually expected to go away shortly (perhaps within the next 4-6 months) as the ITU (International Telecommunications Union, sort of like a "global FCC") and many countries have already done away with it. the USA is one of the few to still have a morse code requirement for HF bands. this is a ideological and philosophical issue more than anything, it has nothing to do with technical issues. long before SSB and FM were used, CW (morse code) was the predominant mode and it was a requirement to know it. these days, not even US Coast Guard radio operators are trained on morse code. so the FCC is catching up a little bit, and i expect that there will be a morse code-less HF license class well before this year is out.


Quote:
In your "101" post, you stated that 462/467MHz radios were general purpose (no license required) radios. I don't understand that part if it lies above the 50MHz mark.

oh, maybe you have a basic misunderstanding about something -- hams don't own ALL the spectrum above 50MHz!!! hams have been allocated tiny little chunks, that's all. other chunks are used for hundreds of other purposes, including police, EMS, fire, military, coast guard/marine, national park service, business band radios, taxis, aircraft, cellphones, NASA, and so on. even your garage door opener has it's own band, as does the 802.11 wireless router you probably have at home. things you don't even think about, like the little RFID tags used to prevent shoplifting, have their own bands.

along those lines, the FRS (family radio services) and GMRS (general mobile radio services) have bands allocated in the 462/467MHz range. these are "the new CB's" -- walkie talkies sold in pairs EVERYWHERE (walmart, sears, you name it) and seen at amusement parks, ballgames, and soccer fields, etc so kids can stay in touch with their parents, hunters in a group can talk to each other, and so on. power limited and with fixed antenna sizes, they are channelized like a CB to keep operation simple. "mom, i'll be on channel 2, mmm-kay?" is all it takes. FRS, no license required. GMRS, you just need to send the FCC a filled out form and $50(?) to get a 5 year "family license" or something like that.

due to power limitations, there is no such thing as an FRS mobile radio, so you are limited to the little walkie talkies and about 2 miles range (approx). no FRS repeaters either to help things. so an FRS radio is not a substitute for a ham radio in all cases. you can't get the same range simplex nor can you utilize repeaters for even more range. on the other hand, FRS radios are dirt cheap, and if you are in a caravan of cars they sure are handy to use to talk between them.

jim aka the wrooster