Soundcard Isolation Project - VA3CR

1 Introduction
1.1 Scope - This manual describes the design and assembly of an interface between a PC and a SSB rig.
Included in this manual are sections describing the theory of operation of the interface, material list and
parts ordering guidelines, assembly procedures, system setup and testing, and web links to find software
for operating in PSK31, MFSK16, RTTY, SSTV and CW using the sound card in your PC as the signal
processor.
1.2 Intended Use - This design has been created for the amateur radio community to encourage more
hams to enjoy the pleasures of the new sound card digital modes. This design is ideal for ham club
construction projects and for individual hams who likes to build their own equipment. The end result is a
solid interface for use with sound card modes such as PSK31, MFSK16, RTTY, Hellschreiber and SSTV.
1.3 Copyright and Ownership - all material in this manual is copyright (c) 2001, Discovery Bay
Computing. Copies may be made of these materials, for the personal use of licensed radio amateurs. NO
commercial use of the designs may be made without express written consent of Discovery Bay Computing.
1.4 Caveats and Disclaimers- the designs represented in this manual have been tested in on the air
amateur radio operation and are believed to be accurate. Clint Hurd, and Discovery Bay Computing are
not responsible for errors, mistakes or omissions made by others when building from these designs. No
claims are made to the use or application of the principles in these designs or fitness for any particular
purpose. Clint Hurd and Discovery Bay computing are NOT liable for consequential damages resulting
from the use of these designs.
1.5 Features - The main features of this design include:
• Ground paths between the PC and the SSB rig that travel through the interconnecting cables
are completely eliminated through the use of transformers and an opto-isolator.
• Potentiometers are provided on both Rx and Tx to allow easy level adjustment during
operation. Knobs are located on the top of the enclosure for easy adjustment.
• LED provided to show when the PC PTT control line is activated.
• Switch provided to enable/disable automatic PTT, or to force the rig PTT ON for manual
operation and test.
• Design implemented on a PCB to reduce wiring lengths and simplify assembly.
• Packaged in a small enclosure consistent with the reduced size of the modern transceiver.
The enclosure measures 4.1”w x 2.7”d x 1.6” h.
• Templates provided for hole location on the enclosure and top panel.
• Panel label overlays provided for top and rear panel.
• Can be interfaced to either the rig’s microphone/line out or to a single accessory port on the
rig.
• Interface can be configured for solid state drive of PTT or for relay contact closure for use
with older tube type transceivers.
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