297 lines
15 KiB
Plaintext
297 lines
15 KiB
Plaintext
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An Amateur Packet Radio Overview
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by
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Rich Bono (NM1D)
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October, 1990
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(revision 1.2)
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The following is the result of a non-amateur asking some basic questions
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about amateur packet radio. Several of us thought that this information
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would be useful to others who are interested in amateur packet operations.
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Thanks to Tim Dayger for asking the right questions, and to Patty Winter
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(N6BIS) for her editing skills. I hope that this will be of help to many
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others. You may reproduce and distribute this as long as my credits remain.
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Rich Bono (NM1D)
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Our potential amateur packet radio operator asks:
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I've used networks, on-line services, and bulletin board systems (BBS) for
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years, but I've never really paid much attention to amateur packet radio.
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I'm starting from scratch, and need to have some idea of where to begin.
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Just what IS amateur packet radio?
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Amateur packet radio is (yet another) digital transmission method available
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for use via amateur radio. It provides 'error free' transmission and
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reception of messages (information/data/etc.) between two stations. This
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error-free capability is a prime consideration. Error free in this
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context does not mean that your typing or spelling mistakes will be fixed,
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but that all transmitted 'data' will be received 100% intact, as sent. In
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fact, if the data cannot be delivered 100% intact, the transmission is
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eventually aborted and the user is informed that there is no longer a
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connection between the two stations.
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The 'packet' in 'packet radio' comes from the method of transmitting your
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information over the air. Your data is broken up into packets (or blocks)
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that are transmitted. Each packet contains the sending and the receiving
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station call-signs and some optional routing information. A packet can
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contain from 0 to 256 data (or information) bytes. The users normally do
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not need to be concerned with this 'packetizing' of their messages. Each
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packet is sent and then acknowledged by the receiver when received. If a
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packet is not received correctly, then it is automatically re-transmitted
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(up to a maximum number of times). You normally don't have to know about
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all this to use packet radio. The 'packetizing' happens automatically,
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without any thought or actions required by you.
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One of the more popular protocols used for amateur packet radio is known as
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AX.25. This is somewhat similar to the commercial X.25 standard. There is
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also a growing TCP/IP user base. If you are not network oriented, then the
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details of these protocols are not important to you as an operator of a
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packet radio station.
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Be aware that most packet radio operation at this time is at 1200 baud.
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This will seem slow when compared to what it happening on networks, and on
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telephone BBSs.... but what is gained is world-wide access, for NO COST.
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Once you have your equipment, and your license, there are no fees (except
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for the electricity that your computer and other equipment use). There are
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a growing number of amateurs who are experimenting with 2400 and even 9600
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(or higher) baud operation, so it shouldn't be too long before these faster
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rates become very popular!
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What kind of equipment do I need, and how do I use it with my PC?
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Since you own a PC, you already own the most expensive part of an amateur
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packet radio station. The other piece of equipment that you need is the
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TNC (terminal node controller). The TNC contains all the software and
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special hardware that you need. It actually contains the modem (to
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interface with your radio) and (usually) a microprocessor with the packet
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software contained in EPROM. You interface your PC (or even a simple dumb
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ASCII terminal) with the TNC via serial RS-232. Use your favorite terminal
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emulation software on your PC (the same software that you use with your
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telephone modem will probably work fine). This is just as easy as connecting
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your computer to a modem. If you don't want to use the serial port of your
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computer, there are TNCs available that will plug directly into the bus.
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If you don't have a PC (personal computer), then almost any RS-232 ASCII
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terminal will work with most of todays TNCs.
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The most popular packet frequencies in the USA are in the two-meter band
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(144-148 MHz). Check out the following frequencies (they may be different
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in your area; ask a local amateur if you don't hear anything). Even
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the typical 'police scanner' can be used to listen to these frequencies:
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145.01, 145.03, 145.05, 145.07, 145.09 MHz
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If the above are busy, many areas also use:
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144.91, 144.93, 144.95, 144.97, 144.99 MHz
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Yes, this is with an average FM transceiver set for SIMPLEX operation
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(transmitting and receiving on the same frequency).
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If there are packet radio transmissions you should hear a sound like:
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BBBBbbbbbrrrrraaaaaaappppppp
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How much technical or hardware proficiency is required to use a packet radio
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system?
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If you can plug an RS-232 cable into a modem, and wire the TNC to your
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radio, then you have all the ability that you need. I am sure that there
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are hams in your area who would be glad to help you if you are not
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comfortable with wiring a microphone connector. Most TNCs connect to the
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microphone plug of an FM transceiver, normally only needing push-to-talk and
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transmit audio connections, and a connection to the speaker audio output
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from the FM receiver. This consists of about five wires, and can usually
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be done without removing the covers of the radio (these are normally
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external connections).
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Installation really is very simple, and once it is done, there is virtually
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no maintenance. Just plug in your TNC in place of your microphone and
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external speaker, and you're on the air... to return to voice
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operation, plug in your microphone. If you like, build a simple switch box
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to allow easy changing between your TNC and voice operation. I don't
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recommend it, but some people wire the TNC and microphone in parallel, so
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that they don't need to change the plugs, or switch anything at all.
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What's out there for me to access via packet radio and what potential is
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there for growth?
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This is the interesting part! I believe that packet radio is still in
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its infancy. It seems like every day a new application for packet radio
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is announced... some are good ideas... others not. By the time you
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read this, a lot of the information presented here will probably be out
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of date; yes this technology is progressing!!!
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Here is a *simple* list that barely highlights some of the available uses of
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amateur packet radio.. I am SURE that I have forgotten something and left
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it off the list:
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EMAIL:
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At this time we have world-wide email (electronic mail) distribution.
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I personally have received email from a few continents, and from all
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over the USA. Of course, this is limited by the amateur radio rules and
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regulations, so there cannot be any commercial messages.
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Local networks:
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Here in New England we have connectivity over most of the region. I
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can connect to other stations from the following areas consistently:
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Canada (Montreal), Vermont, New Hampshire, Maine, Connecticut,
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Massachusetts, Rhode Island and New York. I should note that I am
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located about 10 miles north of the MA/NH border (in Derry, NH).
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Of course, on the HF (high frequency) bands there can be world-wide
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connectivity, depending on many factors.
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PacketCluster-DX spotting:
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This is a specialized system that allows a couple of hundred users to
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be connected to the same system at one time. It is used by those
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amateur operators who seek contacts with rare stations throughout the
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world. When any one user 'finds' a rare station on the air, he
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simply types the information (call-sign, frequency and mode) into his
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terminal, and within a minute or so, all of the other users are
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informed of the rare station!!! So-called "DXers" (people who like to
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hunt these rare stations) LOVE this system. These users can be spread
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over a wide area. Our local packet cluster system has connectees
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from Maine to New York.
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DOSGATE:
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A system that allows you to execute programs remotely. A DOSGATE
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system may have many programs for you to use over the air. You
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don't need to download the programs to use them; you are actually
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running programs remotely. DOSGATE allows those who don't have a
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computer to run programs via packet radio.
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For example, my DOSGATE system has the following programs available
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for use by remote packet users:
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AUTOEXAM: Take sample amateur exams from Novice to Extra. You can
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use AUTOEXAM as a study guide, or to see if you are ready for
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a certain license exam.
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SeeSats: Real time satellite tracking. Informs you of where the
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current OSCAR (and other) satellites are located.
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AUTOCALL: On-line amateur radio USA call-sign lookup database.
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Simply enter the call-sign of any amateur radio operator in
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the USA and it will print out the name, address, license class
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and previous call-sign (if any).
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GAMES: Several adventure-style games that can be played on-line.
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Repeater database: A database of many of the repeaters in the area.
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Gateways:
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Even though you may not own any HF or UHF equipment (many packet
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radio operators only use a simple hand-held VHF transceiver), you can
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gain access to other bands and operating modes by using a gateway. A
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gateway allows connectivity between two normally non-connectable
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communication technologies.
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In many areas not only are there major BBSs on the standard two-
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meter Technician class frequencies and the 222 MHz Novice class
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sub-band, but there are cross-band gateways available as well. A
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Novice on the 222 MHz band can connect to a station on the 145 MHz
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band by going through a gateway and be able to communicate with
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many other amateurs.
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Public Service:
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Many packet stations are used to help out with sending messages
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during disasters. Amateur radio operators help out whenever they
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can, and many hams have their packet stations ready for portable
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operation to help when needed. There are many training exercises
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during each year to help practice and test the readiness of the
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emergency stations.
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OSCAR Satellites:
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OSCAR stands for Orbital Satellites Carrying Amateur Radio. We have
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our OWN satellites in orbit that are dedicated for amateur radio use.
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There are some satellites that are dedicated to packet radio
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(sometimes called "PACSATS"). These are for 'store-and-forward'
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operations to help distribute packet traffic around the world.
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Bulletin boards:
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These carry postings similar to the stuff on Usenet (or telephone
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BBSs) and often have archives of useful files (such as local ham
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license testing sites). These are usually the same packet nodes that
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transport email.
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File transfers:
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Better at 56 Kbaud (as some hams are doing), but feasible at 1200
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baud. On TCP/IP, you just start it and forget it, so you can do it
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overnight or at some other time when you don't care whether it takes a
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while.
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Databases:
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In some areas there are HAZMAT (hazardous materials), call-sign,
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and repeater databases accessible via the network.
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Station-Station:
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I almost forgot.. many people simply enjoy chatting with their
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neighbors.... This could be with people across the street... or in
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the next state... or half-way around the world!
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I am sure that I have missed something. You asked about potential... as I
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mentioned at the beginning, we are just getting started!!! Many people are
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just finding out about packet radio. I believe that the only limitation is
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our imagination!! We could have a world-wide network (we do currently have
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a 'slow-speed' world-wide network) in the near future... It just takes a
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little imagination...
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How much will a packet radio set-up cost me? How COST EFFECTIVE is packet
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radio?
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Well, if you own the PC already... TNCs can be purchased from about
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$120.00 on up. There are a few for less money, and several that provide
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for operating on many digital modes in addition to packet radio (i.e., the
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Kantronix KAM will provide for packet (HF:300 baud/VHF:1200 baud), AMTOR,
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RTTY, ASCII, NAVTEX, WEFAX, CW (Morse code),...).
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If you already own an amateur FM transceiver (or an HF SSB transceiver) then
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you have all the equipment needed. If not, a two-meter FM transceiver can
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be purchased for used from $100-250.00, new from $300.00 on up.
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Cost effective.... Hmmm, well first be aware that amateur radio cannot be
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used for any commercial or business purposes... But where else can one get
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hours (years) of enjoyment and service out of $470.00 ($350 for a radio and
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$120 for a TNC, assuming you already have the computer or terminal). Note:
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This stuff can be contagious.... be forewarned!!
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What legal issues do I need to consider regarding packet radio? Do I need a
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license?
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Yes, you need a valid amateur radio license. There is (in the southern New
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Hampshire area) packet radio activity on the Novice bands. But if you want
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access to the mainstream of packet radio, you will want at least a
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Technician amateur radio license. (Although, as mentioned earlier, some
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areas have an active packet radio network that is accessible with the
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Novice amateur radio license.)
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I've tried reading about amateur packet radio, but a lot of it is Greek to me.
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Please suggest some reading materials such as books and magazines that my
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campus or local libraries might carry.
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There are a few books, etc... but I have found that most assume that you
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already know about amateur radio. You need to find what we call (ready for
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another term?) an "Elmer". An "Elmer" is a friendly, helping amateur radio
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operator who will take you under his/her wing to help and guide you as much
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as you need. I hope that you can find someone to help you... it takes a
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special kind of person to be an 'Elmer' (gosh I hate that term).
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Good luck with your packet radio activities. If you find this information
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helpful, I would be glad to hear from you.... How? Simply send me a message
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via the amateur packet network, NM1D@WB1DSW.NH.USA.NA from anywhere in the
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world!
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