Packet Radio A gentle introduction for Amateur Radio Operators
Packet Radio A gentle introduction for Amateur Radio Operators
Agenda
• Joe – who ?
• What IS Packet Radio ?
• How is it used ?
• How can I get started ?
• Advanced Packet
• Questions
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Joe Who?
• Ham since 1974 – WN3YKP, WA3YKP, AA3YKP • Extra since Nov. 2012 – AG6QO • Profession – BSEE, M. Eng.
– Computer / Controls Engineer – Photovoltaic Microinverters
• Affiliations – BARK, Yolo ARES, ARRL, IEEE
• Find me: – Ham info: http://ag6qo.com/ – Professional Info: http://www.linkedin.com/in/joedeangelo/ – Email: [email protected] – BBS: AG6QO@AG6QO.#NCA.CA.USA.NOAM
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WHAT IS PACKET RADIO?
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What IS Packet Radio ?
• In colloquial Amateur use, the term “Packet Radio” is used loosely to refer to digital modes for transferring data from one point to another via radio.
• While technically, the term “packet radio” can refer to any data link method which employs “packets”, in the Amateur community, it is often used and even mis-used in a variety of ways.
• Most often, in the amateur world, “packet” refers to the transfer of data, over a data-link using the AX25 protocol, most often used on VHF bands, but increasingly on HF.
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Packets
• A packet is a bundle of bits and bytes passed over a data link. In AX25, it is also called an ‘HDLC frame’.
• AX25 does this in such a way that it’s integrity can be guaranteed at the receiving end. It does this via a ‘frame-check-sequence’ using ‘Cyclic Redundancy Check’.
• It contains a ‘header’ and a ‘payload’. The header helps to direct the packet to the correct destination and determine whether it arrived without error. You can think of the payload as a letter, and the header as the addressed envelop.
• Packets are used on the wired internet, cellular networks, and mesh nets. A network consists of ‘nodes’ through which your envelop passes. Think of them as post offices.
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Packets and Nodes
• Data Link Layer • AX25 Protocol • Reliable transmission of data frames between two nodes connected by a physical layer • Allows two stations to reliably exchange packets (error-free). • Specification : http://www.tapr.org/pdf/AX25.2.2.pdf
• Connection Layer “on top of” the Data Link Layer
– Allows multiple stations to connect in “circuits” – Don’t need to know specific “route” to remote station.
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‘packets’ or ‘frames’ of data bytes
CSMA/FM/FSK – ‘bitstream’ over rf
NETROM, UNODE, Knet – ‘connections’
AX25
Open Systems Interconnection (OSI) Layer Model
Node Connection
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AG6QO Winters
KBERR
Mt. Berryessa
KRDG Redding
Connections vs Unproto
• Unproto – refers to the lack of protocol
– No connection, just single ‘broadcast’
– No retries or error correction
– Used in NCA Sunday night net
• Connections – Use error correction handshake
– Can connect to another persons station or an automated ‘node’ (KBERR)
– Your packets are directed only to the connected station
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A word about capacity
• Radio Speed vs. Channel Capacity
Radio / TNC top speeds: – VHF AX25 1200 baud (~1200 characters / sec)
– UHF AX25 9600 baud (~9600 char/sec)
– HF AX25 300 baud
– Microwave Mesh ~10 million char/sec
• Everyone shares the frequency you’re on, using a method called ‘Carrier Sense Multi-Access with collision recovery’ (CSMA). It does this by retrying if another station ‘steps-on’ a transmission. This has the effect of greatly reducing channel capacity.
• You don’t want to send a radio mail with a 1Mbyte photo attachment on 2m unless you want to wait a very long time and incur the wrath of others trying to use the channel !! (Winlink users, take note!)
• Band-plans exist to attempt to manage the ‘saturation’ levels of packet channels.
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HOW IS PACKET RADIO USED ?
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Wide Range of Uses
AX25 Packet • Keyboard to keyboard QSO
• Winlink email
• Packet BBS radio-mail
• NTS long-haul messaging • Used in FEMA exercises
• APRS
Other • Mesh Nodes
– Radio mail
– Voice over IP
– Real-time Video
• PACTOR / WINMOR , etc.
– Radio mail
– NTS long-haul
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Bulletin Boards
• “Store and Forward” messaging
– No need for the recipient to be online.
• Hierarchical message addressing
– No need to know route – White Pages
• S AG6QO@AG6QO.#NCA.CA.USA.NOAM
– The BBS system will route the message to the recipient’s location, if they exist.
• A form of radio mail without the internet.
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Why Packet?
• It’s faster than spoken word and even the fastest CW.
• It’s accurate. Error checking and correction prevents ‘transport errors’.
• It facilitates recording QSO’s and message handling.
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HOW CAN I GET STARTED?
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Minimum Requirements
• A ‘terminal’ device (or computer)
– Allows you to input (type) characters to send and display characters received.
• A “Terminal Node Controller” (TNC)
– Converts your characters (incoming and outgoing) into audio tones with which to modulate an RF carrier or convert incoming tones to a character stream.
• A transceiver with either a data input or a small circuit connecting the TNC output to your PTT/Audio input/output.
– Modulates your carrier with data and demodulates incoming signals to audio tones.
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Typical Setup
• A ‘Windows’ desktop or laptop with puTTY terminal emulation software. : your choice (sw free)
• A KPC3+ TNC : ~ $200 brand new
• A low cost 2m radio (DR135) : ~ $165 brand new
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Low Power Portable
• Increasingly attractive option: – Raspberry Pi / TNCpi
running BPQ software
– Computer and TNC, require only a few hundred milliwatts
– Capable of everything from unproto to complex Radio-mail/BBS
– Cost of computer and TNC: ~ $100 (sw free)
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• Get the Rpi here: • https://www.alliedelec.com/raspberry-pi-raspberry-pi-3/70816528/
• Get the TNCpi here: https://tnc-x.com/TNCPi.htm
• See AG6QO for a pre-configured image of BPQ software
ADVANCED PACKET
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For Advanced Pursuits
• Real power is in Radio Mail. Check out a previous presentation on the subject: http://ag6qo.com/RadioMail.pdf
• Check out the AX25 protocol specification for the low-down details of packet: https://www.tapr.org/pdf/AX25.2.2.pdf
• For history and a good overview (dated, but useful): – http://www.choisser.com/packet/
• Varmint Al’s Packet Page – contains node lists on 145.050 – http://www.varmintal.com/ahamp.htm
• Raspberry Pi info: https://www.raspberrypi.org/ (order from Allied)
• TNCpi info: https://tnc-x.com/TNCPi.htm
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QUESTIONS?
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Assembling the System KPC3+ TNC
TNC to Radio Computer to TNC
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Connect TNC to Kenwood TM-V71
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TM-V71 KPC-3
Connect KPC3/TNCpi to Alinco DR-135
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KPC3 or TNCpi
Pre-made TNC-Radio Cables
• Order pre-made TNC-radio cables at BuxComm:
• https://packetradio.com/catalog/
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