Sound Card Packet  with AGWPE

Translations and PDF 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

Interfacing to Two (2) Radios to One (1) Soundcard

AGWPE can use one sound card to interface with TWO different radios at the same time. It does this by using the left and right stereo channels of the sound card, in effect making the sound card a "dual port" TNC (see the AGWPE: 2 Radio Setup page on this site for more information about configuring AGWPE for this feature.)

This means you can have 2 different packet programs running, each one sending and receiving data with a different radio on a different frequency. If you use WinAPRS, UI-View, or APRSplus, you could have one radio tuned to the local APRS frequency and the other to the local DX cluster frequency or to an HF APRS frequency.

To run a second radio with the sound card, you'll need to use:

  • for PTT control, the DTR pin on the COM port or pins 8 or 9 on the LPT port
  • for TX and RX audio, the ring of your stereo sound card jacks

Note this dual radio feature will not work if use the Microphone jack of the sound card (for RX audio), since that jack typically has mono only input and not stereo. You must use the LINE IN jack if you want to interface to two radios.

Here's the pin and plug assignments for "dual port" sound card use:





DB9 serial
pin #  GND

DB25 serial
pin # GND

 DB25 Parallel*
pin #    GND









2 or 3

18-25 (any)









8 or 9

18-25 (any)

NOTE 1: Do not use the computer ground pin unless:

  • You are wiring the shield to the computer ground instead of the radio ground (don't wire to both!); or
  • You are using an isolation transformer and need to wire one side to computer ground.

NOTE 2: If you are running Windows XP/2000/NT, you can not use the LPT/parallel/printer port for PTT control. You must use the serial port. The parallel port option will work only with Windows 95, 98 and ME in AGWPE. If you use Windows XP, and want to use the parallel port for PTT control, you can purchase Packet Engine Pro.

1. RX and TX Audio Cables

The RX Audio Cable and TX Audio Cable pages of this site describe how to make cables for a radio which would use the left channel of the sound card and Port 1 in AGWPE. Such cables uses the tip of the stereo TX and RX plugs and the RTS pin on the serial/parallel port plug for PTT control. If you already have a set of cables, they are probably wired in this manner.

If you want to use a second radio with the sound card, you would attach a second audio cables to the ring of the stereo plugs (the right channel of the card or port 2 in AGWPE).

Here are two different approaches for the audio cables:

  • Cheaper but harder -- wire it yourself: Using the cable schematics on the RX Audio Cable and TX Audio Cable pages, add a second cable (single wire shielded) to each sound card plug. The single insulated wire will run from the unused ring (middle conductor) of the sound card plug to the proper pins (RX or TX) on radio #2. The shielding should attach to the ground on the radio but NOT attach to the ground on the computer.

    You'll need to make this alteration for both the RX and TX Audio plugs. You'll also need to add a separate attenuation circuit (see TX Audio Cable) for the second TX audio cable.
  • Easier but a little more expensive -- buy two "Y" adapters (Bill's, WB2JAR, idea): Rather than try to squeeze the wires from both radios into the same sound card plug, use a "Y" adapter. The "Y" plugs into the sound card jack and will accept  two sets of audio cables, one for each radio, into the arms of the 'Y

  • Separates left and right-channel signals. Has a 3.5mm stereo phone plug & two 3.5 mm mono phone jacks.

    Bill suggests Radio Shack part #274-375 ($3.59 each) which even does the channel separation for you!  Of course, you'll need 2 of these adapters -- one for the sound card's LINE IN jack (RX audio) and one for the sound card's LINE OUT jack (TX audio).

    These adapters accept simple mono plugs into their jacks. No need for stereo/3 line cables and no need to worry about "tip" or "ring" assignments. The adapter handles that.

    The silver plated jack on the 'Y' is used for the cable coming from radio #1. It's wired to the tip of the adapter's stereo plug and provides the connection to the left channel of the sound card (AGWPE Port 1).

    The gold plated jack on the 'Y' is for the cable coming from radio #2.  It's wired to the ring of the adapter's stereo plug and provides the connection to the right channel of the sound card (AGWPE Port 2).

    If you come up with still another method for the audio cables, let me know.

    2. PTT Cable

    To control the PTT on the second radio, you'll need to add a wire that will run from the DTR pin of the serial or printer port to the radio and includes a second PTT circuit (see PTT Control cable page).

    You might try one of these methods:

    • A. Wire both PTT cables into the same DB25 (or DB9?) connector.   Here's a diagram that Bill, WB6JAR, created for a DB25 for the printer port. (I don't know if you could shoehorn all of this into a DB9 for the serial port.) To simplify the soldering, he broke off some of the pins going out of the DB25 (that would normally plug into the computer) and used the resulting stubs inside the DB25 as solder points. The downside of 2 cables into one DB connector is that, if you want to use just one radio, the PTT cable for the second radio will always be attached to the DB25 and this might be cumbersome.

      Click on the graphic for a larger view. If you do, use your browser's BACK button to return to this page.

      Click to enlarge

    • B. Make a two cable adapter from DB9 plugs. This "Y" arrangement allows you to split the RTS and DTR signals to different DB9 male plugs. You can then plug  standard PTT control cables with DB9 female jacks into the DB9 males plugs. (Could also work with the LPT port.)

      Solder the DTR wire to the RTS pin in the DB9 male for radio #2. This allows you to use either radio's PTT control cable on either male plug, since both male plugs will be sending the PTT signal on pin #7, even though radio #2 is really getting its signal from the DTR pin on the computer.

      This "Y" arrangement also lets you easily remove the second PTT cable if you're not using it.

      Hint: Put a label on each DB9 to specify if it is for radio port 1 or 2.



    Don't forget to change AGWPE's settings to a "dual port"

Last Updated:


Top of page