Sound Card Packet  with AGWPE

Translations of this site
Most recent AGWPE version is:  2013.415  15 Apr 2013

Introduction
Overview
Computer requirements
Packet Engine Pro

Configure AGWPE
Download and Install
Basic AGWPE Setup
2 Radio Setup
2 Card Setup

Sound Device Setup
Basic Device Settings
Rename Sound Device
Additional Settings
Using the Tuning Aid

Problems?
Program Behavior
Receiving
Transmitting
Connections
Firewalls

AGWPE Features
AGWPE on a Network
Baud Rates & Modes
Remote Control
TCP/IP Over Radio
Tips and Tricks
Traffic Parameters

Compatible Programs:
Setup Help

Radio Interface
Getting Started
Kits and Pre-assembled
USB SignaLink
Receive Audio Cable
Transmit Audio Cable
PTT (TX Control) Cable
2 Radio Modification

About Packet
Packet Overview
Exchange Modes
TNCs and AGWPE
What To Do with Packet
Common Frequencies
Frame Headers
Further Reading
 

TNCs and AGWPE

On the Packet Process Overview page and the TNC Modes page, we saw how important the TNC (Terminal Node Controller) is to the packet process. Just to recap, the TNC:

  • packages (assembles) addressing information and data into a packet frame according to the AX.25 protocol roles -) -- and reverses the process when receiving
  • uses its integrated modem to convert the frame from binary bits to audio tones for transmission -- and reverses the process when receiving
  • employs the AX.25 protocols to establish "connections" between stations that result in error-free frame exchanges
  • can be programmed to send out periodic beacons of information
  • can be programmed to digipeat (relay) packets as a service to other stations
  • may have a "mail box" to receive and store messages while the operator is away

So how does AGWPE fit into this picture?

Original Role of AGWPE

As capable as the TNC was, AGWPE's author, George SV2AGW, saw some limitations and found a way to overcome them. These TNC limitations included:

  • only one computer program at a time could connect to and receive data from the TNC
  • a computer program could only connect to one TNC at a time
  • there was no logic to measure or dynamically adjust timing and traffic settings

To overcome these limitations, AGWPE relieves the TNC of using its built-in logic. It does this by putting the TNC in an operating mode found in most TNCs, called KISS  (Keep It Simple Stupid). When a TNC is put in KISS mode, the modem of the TNC remains functional but all the other logic functions of the TNC are turned off and AGWPE handles them.

Since it is now in control of the packet exchange process, AGWPE can use its logic to measure packet traffic conditions on the frequency and make immediate timing changes. And by providing a way for computer programs to connect to AGWPE rather than the TNC directly, AGWPE lets many programs use the TNC's modem at the same time.

Another side benefit of AGWPE is it can simplify the programming work for programmers writing packet programs. Without AGWPE, programmers had to write code to link to a many different TNCs (not knowing which TNC the program user would have). With AGWPE, they can simply link to AGWPE and let AGWPE handle the job of linking to different TNCs.

AGWPE's Sound Card Mode

The next step in the evolution of AGWPE was to take over the one remaining major function of the TNC, the modem.  This was done by using the computer's sound card as a modem emulator. Then, with the radio input and output hooked directly to the computer sound card and the radio's PTT control handled by a signal sent to a COM or LPT port, a computer running AGWPE can work directly with the radio and there is no need for a TNC!

But there are some functions that a TNC does that AGWPE can not do on its own and so work-arounds were developed:

  1. Digipeat -- a special digipeater program linking to AGWPE can be used for this function
  2. Personal Mail Box - again a special messaging program linking to AGWPE can do this
  3. Watch Dog Timer - a circuit can be added to the PTT cable to prevent continuous, unwanted transmissions
     

Last Updated:
18Aug2015

by Ralph Milnes NM5RM

 

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