EMERGENCY COMMUNICATIONS
FROM THE CLUTTERED DESK OF: John G.Budman- KI6GR November 2001
TCARC PORTABLE PACKET STATIONS
Amateur Packet Radio is the mode most commonly used between or among amateur stations to send digital information over various amateur HF, VHF, and UHF radio bands.
Digital information may be generated by various types of terminals such as computers, teleprinters, GPS units, and Video Display Terminals (VDTs). They are most often referred to in the generic simply as TERMINALS. Each type has its own positive attributes as well as inherent disadvantages.
Digital information cannot be directly transmitted via radio propagation: it must be converted to audio to modulate amateur radio transceivers, and the reverse conversion made to detect or demodulate the received audio back to digital form. The specialized unit that performs this MODEM function, and much more, is the Terminal Node Controller or TNC.
The TNC is connected between the terminal and the radio transceiver. It "talks" digital to and from the terminal, and in "audio" to and from the radio. The emission mode used is Frequency Shift Keying (FSK) similar to what has been used for many years to send teletype information over the air. A single audio tone is at one frequency representing a "Mark" or 1, and a different frequency represents a "Space" or zero corresponding the digital data being transmitted or received. The two tones are fairly close, and are thus "Narrow FSK". This results in a high data exchange rate within the limits of permitted bandwidth.
The radio baud rate for packet on VHF and UHF bands is usually 1200, but some nets operate at 9600 baud. The higher rate requires radios modified to perform within bandwidth limitations as well as TNCs capable of 9600 baud. This is usually an either-or choice dictated by what type packet network is in use in your area. Cross-baud operation is not normally done between nets of two different speeds, unless a dual port TNC equipped digipeater is available..
HF can be and is used for packet, but the baud rate is set at 300 to keep emissions within the narrow bandwidth of 2500-3000 Hertz.
There is a second baud rate to deal with, and that is the rate of data exchange between the terminal and the TNC. That interchange of data is via an RS-232C type (surprise ! There is no uniform standard for RS-232C) serial data port on both the TNC and the terminal. The TNC and terminal must be set in agreement, or no or garbled text results. The major parameters that must agree are baud rate, parity information, number of stop bits, 7 or 8 bit data word, and whether the two units perform "handshaking"; a means of controlling data flow to prevent buffer (holding register) overflow.
The TNC accepts transmit data for sending from, and sends received data to the TNC. A great many functions go on within the TNC to make the linking up of stations and the exchange of communications possible. The TNC is a computer controlled Modem and data processor in it's own right.
The overall network philosophy and the details of how stations perform within the packet network is called a protocol. The most common protocol in use is version AX.25, and although there are subsequent versions and variations, the essentials are common. The protocol instructions and microprocessor codes that govern TNC behavior are most often burnt into an EPROM plug-in chip that call be pulled out and updated to newer versions as improvements are developed ...if you are willing to buy the manufacture's upgrades.
User controlled settings or parameters also modify the TNC operation and are given to the TNC when you are in the command mode; that is not connected to and conversing with another station.
These settings are semi-permanent and not lost when power is removed, unlike most computer memory. This is done by NOVRAM (nonvolatile random access memory chips), CMOS RAM with battery backup, or other means. In this way whatever your last settings were at last power down will remain and be the same whenever you power-up again.
In spite of the foregoing, packet equipment requirements are quite modest. All that is necessary beyond your normal 2 meter voice transceiver is a TNC (around $125-150 new; less used), a serial data cable ($6-8), a terminal of any type (from free to whatever you want to spend), a printer is nice to have (free to $??), and a connecting cable for audio and PTT line to your transceiver (about $10 or ...free).
Packet operates simplex on one chosen frequency. There are no offsets, sub audible tones, and dual antennas and duplex tuned cavities required. Any station can be used to repeat (digipeat) and route traffic destined for another station if the station owner turns on that function (parameter) on and leaves his equipment on. Frequencies chosen for packet should be one sanctioned for that band plan by ARRL.
Packet is relatively error free. Sent within each frame of information is checksum or parity information. If the checksum is not correct at the receiving station, an acknowledgment message is not sent to the sender. If no "ACK" is seen within a specified time, the original frame is resent by the originator until it is either "ACKd" or the number of permissible reties is exceeded and the connection is disconnected. How and who takes on the resend duties is different when connected to a "Node" station, but that will be covered later.
Setting up and Operating Packet Radio Emergency Stations
These instructions are oriented towards setting up and using an emergency packet station to support emergency responders in critical incidents, and is specific to the equipment described:
- 1. EP-44 Brother serial-port equipped teleprinter,
- 2. J-Pole antenna and tripod mast
- 3. Yaesu FT2400,FT2500, or FT2600
- 4. Kantronics KPC-3 or KPC-9612 Terminal Node Controller
- 5. Power source, cables and miscellaneous equipment
There are two complete stations available from me at short or no notice ready for pickup and transport. Both stations are very similar as described above.
Step 1: Select operating site Confer with the agency you are supporting. Select a site with the following in mind:
- A. Accessibility to your supported agency operations center
- B. Proximity to your power source
- C. Clear field for antenna away from hazards and obstructions
- D. Operator comfort and safety
Step 2: Set up the station: Follow the specific detailed instructions for each unit.
- A. Pay out all cables to ensure they reach the power source and antenna.
- B. Erect the tripod and install the J-Pole. Secure the antenna using the tent stake or other means to insure against wind blow down. Use the supplied coaxial cable to connect the radio to the antenna.
- C. Ensure the audio cable from the back of the TNC is plugged into the front of the FT2400, rather than the microphone cable.
- D. Connect the FT2400 to a 12 volt D.C. power source and observe proper polarity. Ensure that the 12 volt power connection on the back of the TNC is secure.
- E. Install the DB-25 serial cable from the back of the TNC to the EP-44 teleprinter.
- F. Install batteries in the EP-44 and set up the paper holder and paper. Power up the EP-44 and set the serial port parameters.
- G. Power on the TNC and observe that the EP-44 prints the Kantronics banner and that you have the command prompt (cmd:)
- H. Power up the radio and rotate the big knob to either WRS (144.910) or RDG (145.050). Set the volume to 9 or 10 o'clock position and set the squelch for quieting.
Step 3. Operate: Per the Communications plan given by the AEC or other authority, commence communications and traffic handling.
Detailed instructions on setting up the EP-44 are on the following page.
The EP44 Brother Typewriter:
This special little machine is both a letter quality typewriter and a teleprinter. It gives outstanding print quality when using snap-in one-strike ribbons, or is a thermal printer when the ribbon is removed and the roll paper adapter is mounted. The ribbons are very expensive but 98 foot rolls of thermal fax paper are relatively inexpensive when purchased in 6 or 8 packs.
The keyboard is miserable for gifted typists, but is useable and fairly reliable if nothing gets spilled on it. The serial port is on the right side towards the middle of the keyboard. A DB25 cable with male pins on both ends is used to connect to the TNC. The cables for hookup have all been modified internally so that certain wires are cut. They are labeled as nonstandard, and unmodified cables will not work.
The EP44 runs on 4 D size alkaline batteries. All units have AC adapters which supply 6-7.2 volts d.c. with them which connect to a jack in the back. Eventually all units will also have an inline regulator so that they will run directly from 12 Volts DC. The polarity of the power jack is REVERSED on the EP44: center pin is negative.
Upon securing the unit, remove one cell from the battery compartment as there is a small current drain which keeps the settings alive which will eventually drain the batteries. This is expensive and potentially corrosive. For longer storage, remove all batteries.
Upon powering up a dead unit, the serial port settings will have to be set. And whenever the power is interrupted, such as plugging in the adapter, settings may be lost. You must become proficient at restoring the proper serial port settings. It is not difficult and takes 30 seconds.
Two units have homemade roll paper holders and one has the factory holder. Set one wooden ear on one side and set a roll on the metal pin. Place the other ear on the other side so both pins are in the roll. Place the wooden bar in the space between the ears with the protruding plastic edge towards the keyboard hooked under the edge of the paper feed guide and rock it into place by rotating the top of the bar towards the rear of the machine. The factory paper holder requires no instruction but the plastic is delicate. The roll feeds from its underside.
The [CODE] key is the
The standard settings for the port at labeled near the display LCD. When initially powered on, the unit is off line and says so on the LCD. A thumb wheel on the right front side of the keyboard controls the LCD brightness.
To set the terminal parameters:
The Kantronics KPC-3 or KPC9612
Turn the TNC on and watch for the copyright banner to print, and the cmd: prompt to appear.
You are now in the command mode and the TNC is ready to respond to your input. At this point you can query to learn what a setting currently is, change a setting, or begin a connection.
At cmd:, type MYCALL and
- Type in the call sign for the assigned to this station per the communications plan is use for this exercise. The comm. plan should follow this convention:
TNCs operate in two primary modes (there are others); command line and converse. In command line the full command interpreter is on line and will respond to a valid command. You are talking to the TNC at that point and it expects only commands; you are not connected to any station at that point.
On power-up the TNC will give you a copyright banner and the command prompt:
cmd:
You type in a command and hit enter or
cmd:mycall KI6GR The TNC says:
MYCALL KI6GR
cmd:
If you typed mycallki6gr you would get
Eh?
Cmd:
The TNC wants a space between the command and the parameter. Eh? is Canadianese for "command not recognized"
If you just type the command, you will get a read back of the current setting for that parameter. The full command list is different slightly for each manufacturer and indeed varies and firmware (EPROM) revisions and within models from the same manufacturer. Refer to your manual.
Once you have issued a connect command and upon getting back a **CONNECTED TO WA6BXN** message, for example, the majority of the command interpreter is turned off and you are in the "converse" mode automatically. From that point on everything you type and send at your keyboard will be echoed back to your display device and will also (the main point) appear at your destination station's display device.
To get back into the command mode hit
After entering the correct call signs, each station sets their TNC clock:
- cmd:DAtime yymmddhhmmss (011013133000)
- DAYTIME 011013133000 (This represents year01 mo10 day13 hour1330 & 00 sec.)
To connect, type c
Once connected to a node or a station, you are in the converse mode. Whatever characters you type will be sent when you hit the
All units should have MON On, MCON On and MALL On, so that all traffic can be read by all stations. All stations are set so that multiple concurrent connects are permitted.
Once connected, you are automatically converted to the converse mode. Send your traffic:
From: (IC or BASE) To: HQ MSG NUMBER 01 BK
Simulated message follows. BK
This is a test message to test the link Please acknowledge receipt BK
IC SMITH SENDS BK
END KN
HQ replies:
FROM: HQ TO: BASE (OR CAMP) MSG NUMBER 08 BK
ACK YOUR MSG 01 BK
HQ WILLIAMS SENDS BK
END
***DISCONNECTED***
Keep a running log summary of each message as well as the original printouts of you traffic. Number the messages that you send as third party traffic for each day of operation
Now make up similar test messages as if this was a real operation, but include within the text that it is simulated traffic. Enjoy.
To disconnect simply hit
Of course there is much more to packet than this, but this gets everyone some experience. Remember, I will bring the equipment to the meetings so that you can refresh and learn more.
The instruction manual contains the complete command syntax and further information.
Training exercise of 15 November 2001
For this training we will assume that the hospital (K6SDD-12 must link with the relocation center at the Douglas City Elementary school (K6SDD-14) for medical liaison purposes. It will be assumed that a direct link cannot be made, and must be reached via the node WRS at 144.910.
The first phase is for the hospital to connect to WRS, and then connect to the elementary school
Assuming the TNCs are correctly set, connect to WRS on 144.910:
- cmd:c wrs
***CONNECTED AT NODE WRS***
A node will generally respond to certain letters followed by a
After connecting to WRS, connect to the Relocation Center:
Send your simulated test messages.
To disconnect hit
GLOSSARY OF TERMS (ABBREVIATED LIST. ~ before word indicates a command)
Here are some terms and commands for those who are not familiar with packet:
GLOSSARY OF TERMS (ABBREVIATED LIST. ~ before word indicates a command the TNC will recognize. If a letter is underlined,that will be recognized as a shortcut the same as the full word.)
The key to a successful response is preparedness ahead of need. This MUST include:
The equipment we will use train on are three stations owned by myself. The stations consist of 2 meter transceivers and the antennas, and Brother EP44 typewriters equipped with serial ports and used as dumb terminals. This equipment is available on short notice for emergency use.
The exercises will be simple and consist of:
It is not expected that everyone absorb or retain all the finer points of the material presented. However, the road to proficiency has a beginning, a journey, and a destination. I hope that by concentrating on one particular station configuration, that we will be able to train everyone to a level where they can be comfortable in their ability to use this resource to aid our community.
I will bring at least one station to each regular meeting for those interested to do a little practice and gain more familiarity with it.
KI6GR- John Budman
This page constructed and edited by WB6FZH, Greg
First Draft: November 14, 2001FZH
Last Updated:- July 20, 2005fzh
>
RETURN to TCARC HOMEPAGE
RETURN to EMERGENCY COMMUNICATIONS