Analyzing Audio Frequencies with Oscilloscope and Telephone Capsule

This document details an experiment to understand the listening experience using a telephone receiver capsule.

Experiment Setup

We used a telephone receiver capsule (voice-call) with a signal generator and an oscilloscope. The connections were made as follows:

• Connect the oscilloscope CH1 tip to the telephone capsule terminal.
• Connect the oscilloscope black reference to the signal generator output.
• Connect the signal generator red claw to the same terminal as the oscilloscope tip on the capsule.
• Connect the signal generator negative grip to the other end of the capsule and the oscilloscope.

The oscilloscope is used to analyze the wave and determine the frequency our ears can perceive. By varying the frequency, we can find the minimum audible frequency. A polygraph can help determine if our hearing is within the normal range, approximately 20Hz to 20kHz. The values are then compared with a standard table.

Central Battery System

In a Central Battery Manual Telephone system, the power for handsets is supplied by the local telephone exchange. The operation is similar to a manual system, but the signaling is different. When a subscriber removes the handset, a signaling device is activated at the operator's board. The call completion is similar to the manual system. When subscribers replace the handset, the signaling device is activated again, breaking the connection and preparing the circuits for a new call.

Oscilloscope Signal Analysis

On the oscilloscope screen, a signal of 1 Vpp (v1) is set at point x10. Changing to x1 modifies the signal, increasing or decreasing the attenuation. To calculate the gain in decibels (dB), we modify the signal and enter the new value (v2) seen on the oscilloscope. The calculation is: 20 * log10(v2/v1).

Example:

If we modify the tip to x1, there is no gain of 10 times, and the new voltage value (V2) will be 10Vpp. The calculation is: 20 * log10(10Vpp/1Vpp) = 20 * log10(10) = 20dB.