Phase Equalization Research Articles

The Design of Wide-Band Scatter Systems

The modulation bandwidth that a scatter system can handle is mainly determined by the transmitting and receiving antenna beamwidths. A higher carrier frequency, therefore, permits the use of a smaller antenna. The transmitter power may then be chosen to give an adequate carrier-to-noise ratio. A method of reducing the differential delay in diversity receivers which extends the modulation band a given scatter system can handle, has been developed. IF amplifiers in wide-band scatter systems are a particularly difficult compromise between performance and ease of maintenance. To date it has not proved possible to use phase equalizers on these circuits, and between 1 and 2 db of threshold must thereby be sacrificed. IF combining is attractively simple, but even with delay correction, it is doubtful whether the phase can be locked to the required accuracy at low carrier-to-noise ratios. The base-band combiner is more complex but can be made to operate up to modulation frequencies of 5 mc. Its operating range is somewhat restricted, however.

The Use of Phase Equalizers to Improve the Transient Response of a Television Transmitting System

The Use of Phase Equalizers to Improve the Transient Response of a Television Transmitting System

Precision carrier frequency control and modulation phase equalization of base transmitters in a mobile radio system

Precision carrier frequency control and modulation phase equalization of base transmitters in a mobile radio system

Study of earthquake mechanism by a method of phase equalization applied to Rayleigh and Love waves

Rayleigh waves and Love waves are used for the study of the earthquake mechanism by the application of a method of phase equalization. In this method, an impulse response is computed from known phase-velocity data and instrument characteristics, and is cross-correlated with an actual record. A comparative study of Love waves from Kern County aftershocks of 1952 and those from Nevada shocks of 1954 strongly supports the hypothesis of a pair of couples rather than a single couple for the earthquake source. Source functions for five Kern County aftershocks are derived from the Rayleigh waves recorded at Weston and Palisades. It was found that the sense of principal motion in the source function is in agreement with the fault-plane solution obtained from the P-wave data. Mantle Rayleigh waves are found to be useful for this purpose also.

The Problem of Phase Equalization

The equalization of the insertion-phase vs frequency characteristics of low-pass filters and low-pass like networks is considered in the article. A method is described for maximally-flat equalization by minimum-pass or all-pass equalizers. The method can be readily extended to a nearly equal-ripple approximation by using Darlington's method of Tchebycheff polynomial series.

A new video differential phase and gain equalizer

ONE OF THE MAJOR PROBLEMS in the transmission of color television signals, of the National Television System Committee type in present use, is that of securing satisfactory differential phase and gain characteristics.

Precision carrier frequency control and modulation phase equalization of base transmitters in a mobile radio system

Distortion-free reception by mobile units of base transmissions is essential in multiple base station mobile radio systems, where adjacent stations are operated simultaneously and modulated with the same intelligence. Phasing and heterodyne distortion factors in overlap coverage areas must be minimized. After many months of laboratory and field testing, a satisfactory solution has been developed and applied to a system using wire lines for base station and control point interconnection. This method provides precision control of carrier frequencies, and phase equalization of modulation by building out the wire lines so that transit times are equal. After two years of operation this method has proven to assure satisfactory distortion-free reception.

A Wide—Band Audio Phasemeter

The problem of measuring the phase angle between two sinusoidal voltages is an important one in laboratory procedure. Phasemeters which can make this measurement accurately over a substantial frequency range have heretofore been bulky and relatively stationary. This paper describes a circuit which results in a phasemeter which is accurate to about 30 minutes, has a dial adjustment which is independent of frequency, operates over a range of from 20 c.p.s. to 100 kc and is relatively small and inexpensive. The principle used is to match the phase shift between the unknown voltages with a calibrated phase shift in the meter channel. This phase equalization is observed on a standard oscillograph which is used only as a comparison instrument. The oscillograph amplifier phase shifts are balanced out with an uncalibrated phase shifter cascaded in the meter channel and do not affect the measurement.

Television Network Facilities

This paper describes television network facilities which are needed to connect studios and other pickup points to transmitters in the same and in distant cities, and discusses their transmission characteristics. Short-haul television circuits may be by microwave radio or over wire circuits. Long-haul television connections may be by radio relay or over coaxial systems of the type originally developed for carrier telephone circuits. Transmission requirements include adequate frequency band, accurate gain and phase equalization, and freedom from interference resulting from excessive noise, crosstalk, or modulation. Radio and wire systems are under development to provide extensive high-quality television networks.

Network Theory, Filters, and Equalizers

Part III is concerned with ladder and lattice filters, attenuation and phase equalizers, and dividing networks. The fundamental equations and design procedures involved in both ladder and lattice filters are reviewed. Tables and charts are given for aiding in the design of M-derived filters having terminal half sections. It is possible in this way, without making calculations other than placing numbers in simple formulas, to design filters having characteristics that will meet most requirements. Consideration is given to filters terminated with other than half sections, particularly MM′ and fraction terminations. A chart is given for the design of MM′ terminating sections, which give unusually good impedance characteristics at the terminals. Fractional terminations, which are used when filters are to be placed in series or in parallel, are considered with particular reference to complementary filters. The factors controlling the cutoff frequencies, attenuation and phase characteristics, and impedance characteristics of lattice filters are reviewed. The attenuation and phase behavior of such filters can be given almost any desired characteristic by suitably locating an adequate number of critical frequencies (i.e., zeros and poles of impedance) in the pass bands, while the behavior of the image impedances can be similarly controlled by the location and number of the critical frequencies in the attenuating bands. Particular consideration is given to the requirements that the critical frequencies in the pass band must satisfy in order to obtain a substantially linear phase-shift characteristic in the pass band. The relationship between ladder and lattice filters is reviewed.