Methods for Measuring Transmission Performance of Telephone Sets
|Publication Date:||1 January 1971|
Scope and Purpose
The purpose of this standard is to describe a practical method for measuring the transmission characteristics of a telephone set by means of objective measurements in a test connection. The test results thus obtained may be used as a means of evaluating or specifying the transmission performance of a telephone on a standardized basis.
The basic accuracy and reproducibility of measurements made in accordance with this standard will depend primarily upon the accuracy of the test equipment used, the care with which the measurements are conducted, and the inherent stability of the telephone and/or transducers under test
Where a given set of measurements is repeated in the same laboratory and by the same operator, a relatively high degree of reproducibility should normally be obtained. However, when comparing measurements made by different laboratories, allowances must be made for the influencing factors mentioned above.
NOTE: An experimental test program based upon this standard indicated that differences of as much as 6 dB could occur in transmit and air-to-air measurements and as much as 3 dB in receive measurements. In most cases, however, these differences can be significantly reduced by means of special correlation studies between the participating laboratories
The method requires a suitable Artificial Mouth. It also specifies a standard Artificial Ear, standard circuits comprising dc power feed and connecting loops, and a standard pressure microphone.
This standard is intended for use in measuring the transmission characteristic over the frequency range most useful for speech, 200 to 5000 Hz. It is to be used for singlefrequency measurements and for measurements with continuously varying frequencies such as slow sweeps.
It is suitable also for measuring the transmission performance of conventional telephone sets equipped with handsets using carbon transmitters and used with 2-wire circuits. It is not intended to be applicable to special devices such as noise-exclusion transmitters, distant-talking transmitters, inserttype receivers, or noise-exclusion receivers equipped with large ear. pads.
This standard uses a standard pressure microphone to measure the sound field produced by the Artificial Mouth and to measure the pressure developed in the Artificial Ear.
Drawings and test procedures as well as other pertinent information have been included as an aid to designers in setting up the tests.