[ML-Hams] Android + APRS

[Kris Kirby]

On Mon, 21 Mar 2016, Jeff Cotten wrote:
> This looks awesome, I want one.
> 
> Products like these will help address the issue of attracting young 
> blood to the HAM hobby.  A further improvement would be reducing the 
> learning curve by explaining what KISS, APRS, and TNC is.  Newcomers 
> have no idea why they should be interested in whatever those acronyms 
> mean.  I only got a taste of what APRS was last night watching a 
> youtube video of some guy running a telnet sessions over his radio at 
> 1200 baud:  https://www.youtube.com/watch?v=f-Be8e2tclU  

A TNC is a Terminal Node Controller, or basically an intelligent message 
processor (IMP), an interface box that allows a user on a dumb terminal 
to communicate with other users through a transmission medium with IMPs 
at both ends. The TNC contains a modem, packet buffer, and interface 
control logic to control a radio transmitter, modulate the transmitter, 
and decode the audio from the receiver. 

https://en.wikipedia.org/wiki/Interface_Message_Processor
https://en.wikipedia.org/wiki/Terminal_node_controller
https://en.wikipedia.org/wiki/Packet_radio

TAPR gave birth to the TNC:
https://www.tapr.org/packetradio.html
https://www.tapr.org/kits_119.html

KISS is a TNC specific serial protocol:
https://en.wikipedia.org/wiki/KISS_%28TNC%29

KISS is designed to place the received packets on the serial bus as 
quickly as possible with as little extraneous information as possible, 
and to do the same on transmit. 

eXtended KISS (XKISS) is a multi-dropped (like RS-485) version of KISS 
that allows for attaching multiple devices (TNCs or computers) to a 
shared serial bus. G8BPQ's node stack supports this, and the Kantronics 
KPC-9612 supports this as well, providing two "distinct" virtual TNCs 
when used in XKISS or KISS mode.

There are hardware TNCs, originally based on RS232 serial 
communications. TNCs have been made that used the Zilog Z80 (TAPR TNC2) 
and Motorola 68HC11 (Kantronics KPC-series). There are now software 
TNCs, for both Windows and Linux which use sound cards. 

The "over-the-air" protocol is called AX.25, which is an extension of 
the X.25 network stack:
http://tldp.org/HOWTO/AX25-HOWTO/x61.html
https://en.wikipedia.org/wiki/AX.25

There are also node stacks, both hardware (TheNet, ROSE) and 
software such as G8BPQ, JNOS, TNOS:
http://www.cantab.net/users/john.wiseman/Documents/
http://kf8kk.com/packet/jnos-linux/thenet-ops-1.htm
https://www.tapr.org/pdf/DCC1993-ImprovedTNCinterconnections-N2IRZ.pdf

http://kf8kk.com/packet/jnos-linux/jnos-ops-1.htm
http://www.langelaar.net/jnos2/
http://www.linux-ax25.org/wiki/TNOS

AGWPE works as both a sound card software TNC and a node stack:
http://www.sv2agw.com/ham/agwpe.htm

There is/was TCP/IP stuff, but it's not used with APRS:
https://en.wikipedia.org/wiki/AMPRNet
http://www.ampr.org/
http://wiki.ampr.org/wiki/Main_Page

Tim, N8DEU, may be a better source for what APRS and packet are than 
myself. I tend to look at things as what you can do with them, as 
opposed to what they are said to be. APRS is many things, part network, 
part application, part message-passing.

One analogy would be a single-frequency network composed of simplex, 
half-duplex repeaters which repeat something like UDP frames of 
information and limited broadcast domain control logic combined with a 
little bit of intelligent message routing.

But 1200 bps half-duplex is slower than it appears to be, however there 
is compression involved in some APRS packets. 

Over-arching project itself:
https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System
http://www.aprs.org/

"Backbone" / "Internet Infrastructure": http://www.aprs-is.net/
IGate: http://www.aprs.net/vm/DCC97/internet/
http://www.findu.com/

Applications:
 Google Maps + APRS-IS: http://aprs.fi/
 http://www.findu.com/

Text messaging from internet to APRS: 
 http://www.aprs.org/aprs-messaging.html
 http://www.findu.com/cgi-bin/entermsg.cgi
 http://www.aprs-is.net/email.aspx
 http://aprsisce.wikidot.com/doc:aprs-messaging-explained

Single-frequency networking:
 https://en.wikipedia.org/wiki/Single-frequency_network
 http://www.aprs.org/fix14439.html
 http://www.aprs.org/fixingLA.html

It's also important to point out that there's more than one way to 
modulate a transmitter. 1200 bps APRS relies on the ad-hoc standard of 
Bell 202 modem + commodity two-way radio = signaling inside of the voice 
bandwidth (300 - 3,000 Hz) without equalization or correction. 

We have other speeds such as:

2400 bps is the fastest speed inside the voice bandwidth (for now). This 
 required special modules to go into the TNC, changing jumpers, etc.
9600 bps GMSK/GFSK using modified radios or special, standardized ports on the radio now.
19,200 bps required special radios and/or special TNCs, or serial cards, 
 or mods to TNC and/or radios (replacing IF filters, tapping into the 
 modulator directly).
56,000 bps required a special ISA card (PI-2) with a Zilog Z8530 serial 
 processor which natively built X.25 frames and performed synchronous 
 serial communications, as well as the GRAPES modem and modified 
 transverters: http://www.wa4dsy.net/rfmodem.html

And that's just the tip of the iceberg. There are other modes yet to be 
discovered or implemented to maximum the bandwidth of a 0-4KHz audio 
path or 300 - 4,000 Hz audio path. 

V.90 or V.92 maximized the bandwidth of what could be obtained in a 
voice-grade audio path at about 33.6KHz, but those modems are encumbered 
by patents. Carrier frequency is 3429 Hz, however. But those modems also 
don't work in half-duplex -- they are full-duplex only. 

--
Kris Kirby, KE4AHR
Disinformation Architect, Systems Mangler, & Network Mismanager