W7JI Sound Card Interface

Inexpensive, Easy to Build Sound Card Interface. IT WORKS!


Biil of Materials
Description                            Part No.            Cost      Qty    Total
Mouser 600-600 Ohm transformer         42TL016-RC          $1.86     X2     $3.72
Mouser 1K potentiometer                312-1001F-1K        $1.40     X2     $2.80
Mouser 1K 1/4 watt resistor            66-CMF1/41001FLFTR  $0.06     X2     $0.12
Mouser 1N914 Signal Diode              512-1N914           $0.06     X2     $0.12
Mouser 0.1 uF/50v capacitor            647-QYS1H104JTP     $0.21     X2     $0.42
Mouser Opto-Isolator                   78-4N25             $0.27     X1     $0.27 
Mouser 6 Pin IC socket                 571-1825093-1       $0.53     X1     $0.53
Mouser Bud Project Box (3.1x2.1x1.1")  563-CU-1941         $2.10     X1     $2.10
Mouser Shipping                        Shipping            $4.99     X1     $4.99
Parts-Express perf board (2.3"x1.9")   320-450             $0.80     X1     $0.87
                                                                     TOTAL $15.96 

Who designed it:
Louis Burke, W7JI, designed this circuitry for a sound card interface. It is simple and can be built in one evening. 
Cost for parts is low and best of all ... IT WORKS!

Where it is used:
Several of the 
W7JI interfaces
 are in use in the BCVHFA Communications Center. Tests on various sound card interfaces have been made. No noticeable difference in performance between this circuit and other commercial sound card interfaces was found. The 
W7JI interface performed adequately.

BCVHFA also uses a W7JI interface at the repeater site to directly interface the repeater to the on-site Echolink computer. 

Several BCVHFA members have built the W7JI interface for home base station use. The local volunteer emergency communications group has several 
W7JI interfaces 
for digital emergency communications.

This circuit works well for PSK-31/64, RTTY, ALE and several other sound card modes. 

Features and use:
The trimmer potentiometers allow setting the sound card audio level without having to reset the microphone gain or audio gain on either the rig or computer. This is a great operating benefit when rapidly switching from voice mode to digital mode.

If the autopatch connections are not being used on the rig, then the audio input and audio output of autopatch connection port on the back of the rig maybe used to interface the audio and allow control of the PTT. 
CAUTION:
 If the computer audio output is fed into the audio input on the rig and sound card mode audio is generated from the same computer, then the operating system dings, dongs, and alert sounds may be transmitted. Adjustment of audio mixer controls may possibly minimize audio alert sounds. Alternately, an inexpensive USB sound card dongle may help by providing a dedicated sound card for the digital mode software.