Transmitter Characteristics Research Articles

Apparatus for the Direct Measurement of Force-Displacement Characteristics of Mechanical Systems at Audiofrequencies

Dynamic characteristics of displacement as a function of driving force applied to mechanical systems are obtained by using a piezoelectric crystal to measure the dynamic force and a parallel plate condenser to measure the resulting displacement. The voltages developed across the crystal and condenser are amplified and impressed on the vertical and horizontal plates of a cathode-ray oscilloscope. In this way a trace of displacement as a function of the driving force for the mechanism attached to the crystal is obtained. The area of this force-displacement characteristic is the energy dissipated by the mechanism per cycle. Viscous dissipation may be easily separated from hysteretic. The reactance and mechanical resistance may be derived from the shape of the oscillograph trace. The apparatus has been used to study the dynamic characteristics of carbon transmitters, the inherent amplification and distortion of microphonic contacts, and the sliding of metal contacts.

Characteristics of Modern Microphones for Sound Recording<!--<xref ref-type="fn" rid="fn1-10.5594_J11954">*</xref>-->

Factors influencing the choice of a microphone for sound recording are considered. The characteristics of a new miniature condenser transmitter and amplifier, as well as a number of other types of microphones now in use, are included.

The Required Mininum Frequency Separation between Carrier Waves of Broadcast Stations

The general problem of interference between adjaceni broadcast channels is discussed in relation to the average distribution of power over the frequency range of typical broadcast signals, the response characteristics of the ear, and the frequency characteristics of transmitters and receivers. The discussion includes a consideration of what may be accomplished by modifying the characteristics of transmitters and receivers, and the extent to which the required modifications depend upon relative field intensity of desired and interfering signals. The conclusions suggest that some rather extensive changes in the frequency allocation of broadcast channels will be necessary in order to provide at least one clear channel capable of high quality program transmission to all receivers.

The Trend in the Design of Telephone Transmitters and Receivers1

This is a report of the Joint Subcommittee on Development and Research, National Electric Light Association and Bell Telephone System. It was prepared by the Chairmen, respectively for the Bell System and the N.E.L.A., of the Project Committee assigned to this study. The report reviews the history and present trend of the design of telephone transmitters and receivers, particularly from the standpoint of their response frequency characteristics, and discusses the possibility of obtaining a reduction in the effect of line noise by shifting their points of maximum response. It is concluded that no advantage from this standpoint is indicated inasmuch as it has been found that the distribution with frequency of the extraneous energy on telephone toll lines is approximately uniform over the more important portion of the frequency range. It is further stated that the present trend in improvement of the response characteristics of transmitters and receivers is in the direction of reducing the difference between their maximum and average response.