Sound Card Packet  with AGWPE

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

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

Program Behavior

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
What To Do with Packet
Common Frequencies
Frame Headers
Further Reading

Interface (Computer-to-Radio Cables)

Getting Started

To connect your radio to the sound card in your computer, you'll need an interface. The simplest interface consists of three (3) cables, one each to handle :

  •  RX (receiver audio)
  •  TX (transmit audio)
  •  and PTT (transmit) functions.

On two of those cables (TX and PTT), there will be some simple circuitry built from a few easy-to find components.

Back when sound card packet started in 2000, most hams built their own interface. Soon, vendors began to offer kits or pre-assembled interfaces. Recently, many vendors have been offering an interface that includes an auxiliary sound card. Although these USB interfaces are a bit more expensive, they have become very popular because they provide a second "sound card" that can be dedicated to ham radio purposes. They are also easy to hook up -- just plug one cable into your radio and plug another one into a USB port on your computer.

A radio-to-computer interface for packet is probably the same as one as  would be used for other sound card digital programs such as PSK31 or Slow Scan TV. So, if you already have such an interface, you may be able to use it for sound card packet. (Warning: This may not always be true. Some radios have jacks that use certain pins for HF operations and other pins for VHF/UHF operations.)

Note for 9600 baud operations: Well designed kits, pre-assembled interfaces and USB interfaces usually have isolation transformers on the TX and RX audio lines. Those transformers work fine for 1200 baud AFSK operations but do not have the correct frequency response range for 9600 baud FSK operations.

Actually, I know of no isolation transformers that will work for 9600 baud operations. You may be better building a special 9600 baud interface omitting any isolation transformers, but understand the risks involved in directly coupling two devices -- computer and radio --  that may be at different voltage potentials. Those risks include ground loop noise and conceivably even damage to your radio or computer.

If you build your own:

  • You will find pages on this site which give advice on building the three cables which are needed for an interface. Look in the menu in the left margin of this page -- under Section 7 -- to find pages for the Receive Audio, Transmit Audio and PTT cables.

  • Make sure you build the interface long enough to reach from your radio to your computer sound card jacks, especially for fixed position radios and computers. BUT keep them as short as possible to reduce the chance of picking up stray RF (radio frequencies) or EMI ( Electro Magnetic Interference ).
  • Be sure to use cables with a shield in them to help prevent stray RF from entering the cables.
  • Use isolation transformers in the Receive (RX) and Transmit  (TX) Audio cables (except for 9600 baud packet ) and an opto-coupler/photo-transistor in the PTT cable to break the ground path between the radio and computer.
  • At least two of the cables will need small circuits. You'll find other variations at WM2U's PSK31 site Circuit components should be readily available at local electronics store or on-line.

Going beyond simple circuits, you'll find instructions for home-brewing the "Cadillac of sound card interfaces" in the March 2002 QST, p 31.  Bob Lewis describes how to build an interface for ICOM HF rigs with many deluxe features.

Also, take a look at Skip KH6YT's TX audio-triggered (VOX) PTT interface which was featured in a QST article in June 2009 (p.30):   The beauty of Skip's design is that you won't need a serial, parallel or USB port for triggering the radio's PTT circuit; the TX audio will trigger it.

Stephen Smith WA8LMF has also designed a VOX operated PTT interface. See his circuit on his Tone Keyer web page.

If you want to use your sound card with 2 radios, you'll need a more complicated interface (see cable2radio.htm).  

Special Tip: If you want the flexibility of easily switching your interface between different radios, you might be interested in this cable construction trick.

Last Updated:

by Ralph Milnes NM5RM


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