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Packet radio
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<> INTRODUCTION TO PACKET RADIO >
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Simply stated, Packet Radio is digital comncation between
terminals and/or computers using radio as the transmission
medium. It is usuallydoe ith small home computers such as
the IBM PC but can be anything as simple as a dumb terminal o
ascomlex as a 370. The only requirement is that it have an
RS-232C interface.
The terminal or ompuer R-232C interface attaches to a
Terminal Node Controller (TNC). The other side of the TNC
atache to aradio. This could be any radio, not just an FM
radio. Although I don't know of anyone ho hastried t, I see
no reason that a CB radio would not work (I don't know what the
legality of tis woul be).
The usual mode of operation involves two stations communRadio and using a modem.
I fact, prt of th TNC is a modem.
Many such conversations could be taking place on the same radiofrequencyat the sae time. A system involving Carrier Sensed
Multiple Access with Error Detection CSMA/ED) i implementd in
the TNC. This keeps the stations from interfering with each
other most o the time ad when theydo interfere, it detects
that fact and causes re-transmission. A check-sum t the end ofeach packet nsures that all data exchanged is error-free.
Addressininteractively with he entire grop.
Most curent activity is among Amateur Radio operators using
frequencies assignedthe Amateur Raio Service. A first this
was done using a Special Temporary Authorization (STA) fro the
FCC. The mateur Radio rues and regulations have since been
amended to provide for this mode f digital communcation.
Smallhome computers such as the IBM PC but can be anything as simple asa dumb terminal o as complex as a 70. The only requirement is that it have an RS-232C interface.
The terminal or coputer RS-232C inteface attaches to a
Terminal Node Controller (TNC). The other ide of the TNC
attahes to a radio. Ths could be any radio, not just an FM
radio. Although I don' know of anyone who as tried it, I see
n reason that a CB radio would not work (I don't know what he
legality of this wuld be).
The usual mde of operation involves two stations communicating
justas they would using moems and telephone line. From the
users standpoint, thereon (CSMA/ED) is impemented in
the TNC. Ths keeps the stations frm interfering with each
other most of the time and wen they do interfere, itdetects
that fact and cases re-transmission. A check-sum at the end of
eah packet insures that alagroup of stations to convrse
interactively with the entire group.
Most crrent activity is among Amteur Radio operators usingfrequ and UHF bands have also been used with smilar
results. 1200 baud hs been the usual data rate n these bands
using unmodified voice-grade rdios.
There has recently ben a substantial increase in acket Radio
actia high altitude
where it cn be used as a repeater with overage of almost
one-half th earth. Amateur radio operators using teir home
stations have been usng this satellite to comn inteesting way of combining two
hobbies,
adio and home computers.
ChuckGreen - N0ADI
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