Browse Prior Art Database

TWO-WIRE AUDIO ACCESSORY FOR TWO-WAY RADIOS

IP.com Disclosure Number: IPCOM000007704D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-16
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

Robert B. Ford: AUTHOR

Abstract

Two-way portable radios ohen are used with a remote speaker/microphone (spkr/mic) accessory. The cable used in present designs has four or more wires. Field failure data indicates that the primary cause of failure is associated with the cable. Either wires damage or their many solder connections fail. To keep a small cable size, the many wires are of a small size and are not physically strong. A way to improve reliability as well as cost and manufactur- ability is to reduce the number ofwires required.

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Technical Developments

TWO-WIRE AUDIO ACCESSORY FOR TWO-WAY RADIOS

by Robert B. Ford

  Two-way portable radios ohen are used with a remote speaker/microphone (spkr/mic) accessory. The cable used in present designs has four or more wires. Field failure data indicates that the primary cause of failure is associated with the cable. Either wires damage or their many solder connections fail. To keep a small cable size, the many wires are of a small size and are not physically strong. A way to improve reliability as well as cost and manufactur- ability is to reduce the number ofwires required.

  By using circuitry inside the radio end connec- tor of the spkr/mic, the accessory design below allows use of only a two wire cable (or coax) to the speaker/mic head.

OPERATION IS AS FOLLOWS

The radio circuits shown operate in a simplex manner whereby when during the transmit mode,

with the radio PTT Input at a low state (0.6vdc typ- ical), the Mic Input amplifier is active and the Rx Audio amplifier is inactive. Conversely, when the PTT Input is at a high state (4.6vdc typical), the Rx Audio amplifier is active and the Mic Input ampli- fier is inactive.

  The PM switch shown is a normally closed type. When not pressed, in the receive mode, the switch connects the speaker across the mic cartridge and the dc voltage on the cable wire is low. This condi- tion does not cause Ql to conduct and the PTT Input remains high. The active Rx Audio amplifier drives the speaker via C2. Audio filt...