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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

10/22/2017 Joe DeAngelo 2

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


http://ag6qo.com/

http://ag6qo.com/

http://ag6qo.com/

http://www.linkedin.com/in/joedeangelo/

http://www.linkedin.com/in/joedeangelo/

mailto:[email protected]




WHAT IS PACKET RADIO?


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.


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.


https://en.wikipedia.org/wiki/High-Level_Data_Link_Control

https://en.wikipedia.org/wiki/High-Level_Data_Link_Control

http://practicingelectronics.com/articles/article-100003/article.php





https://en.wikipedia.org/wiki/Cyclic_redundancy_check

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.


‘packets’ or ‘frames’ of data bytes

CSMA/FM/FSK – ‘bitstream’ over rf

NETROM, UNODE, Knet – ‘connections’

AX25

Open Systems Interconnection (OSI) Layer Model

http://www.tapr.org/pdf/AX25.2.2.pdf

http://www.tapr.org/pdf/AX25.2.2.pdf

Node Connection


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


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.


HOW IS PACKET RADIO USED ?


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


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.


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.


HOW CAN I GET STARTED?


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.


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


http://www.hamradio.com/detail.cfm?pid=H0-000229

http://www.hamradio.com/detail.cfm?pid=H0-008739

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)


• 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

https://www.alliedelec.com/raspberry-pi-raspberry-pi-3/70816528/


https://tnc-x.com/TNCPi.htm

http://www.cantab.net/users/john.wiseman/Documents/index.html















ADVANCED PACKET


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


http://ag6qo.com/RadioMail.pdf

http://ag6qo.com/RadioMail.pdf

https://www.tapr.org/pdf/AX25.2.2.pdf

https://www.tapr.org/pdf/AX25.2.2.pdf

http://www.choisser.com/packet/

http://www.choisser.com/packet/

http://www.varmintal.com/ahamp.htm

https://www.raspberrypi.org/

https://www.raspberrypi.org/

https://www.alliedelec.com/





QUESTIONS?


Assembling the System KPC3+ TNC

TNC to Radio Computer to TNC


Connect TNC to Kenwood TM-V71


TM-V71 KPC-3

Connect KPC3/TNCpi to Alinco DR-135


KPC3 or TNCpi

Pre-made TNC-Radio Cables

• Order pre-made TNC-radio cables at BuxComm:

• https://packetradio.com/catalog/


https://packetradio.com/catalog/

https://packetradio.com/catalog/