Amplitude Equalization Research Articles

Comsat's tdma traffic terminal

AbstractCOMSAT has installed two traffic terminals in the Etam earth‐station and is currently installing a third in the new Roaring Creek earth‐station to access the INTELSAT TDMA network. This paper describes the COMSAT TDMA traffic terminal equipment from the supergroup interface to the antenna. COMSAT's 1: N redundancy approach for terrestrial interface equipment and DSI unit back‐up is described as well as electrical path length, amplitude and group delay equalization techniques, special on‐line RF monitoring and failure reporting facilities and the operation and maintenance centre which can operate and perform diagnostic testing on up to four traffic terminals from a central location.

A new approach to FIR digital filters with fewer multipliers and reduced sensitivity

A new approach to the design of efficient finite impulse response (FIR) digital filters is presented. The essence of the proposed method is to decompose the design problem into two parts: the realization of an efficient prefilter and the design of the corresponding amplitude equalizer. It is shown that this method can provide benefits in three areas: reduced computational complexity, reduced sensitivity to coefficient quantization, and reduced roundoff noise.

Is There an Oblique Magnetic Rotator Inside the Sun?

AbstractThe size of the rotational splitting recently observed (Claverie et al., 1981) is correlated with the 12.2d variation in the measurements of solar oblateness observed by Dicke (1976) and implies a convection zone of depth of 0.1 Rʘ. The near equality of amplitudes of global velocity oscillations (Claverie et al, 1981) of the various m components of the l = 1 and l = 2 modes as seen from the Earth viewing the Sun nearly along the equator is unexpected for pure rotational splitting. It is suggested that a magnetic perturbation is present and an oblique asymmetric magnetic rotator with magnetic fields of a few million gauss is responsible. A more detailed account was submitted to Nature.

A new family of active variable equalizers

An active version of the Bode-type variable equalizer has been designed. Variable equalizers are widely used for amplitude equalization in wide-band transmission systems because they possess the unique property that the equalization shape does not change as the amount of equalization is varied. Such a property is especially desirable when equalizing cable of varying length. The active variable equalizer to be described here overcomes many of the disadvantages associated with the conventional passive version, which include the need for inductors, a complex design procedure, and incompatibility with modem electronic control elements. This design also has advantages over other active variable equalizer designs. Such an equalizer is especially applicable to precision equalization at frequencies below 10 MHz. As an example, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sqrt{f}</tex> equalizer can be built with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 9-dB</tex> range having only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 0.05-dB</tex> maximum error. The equalizer is easily built with operational amplifiers and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</tex> networks.

The Effect of Selective Fading on Digital Radio

In the course of development of the DRS-8 Digital Radio System a series of digital propagation trials were conducted over a 51 km path at 8 GHz to determine the effect of multipath propagation on a 40 MHz bandwidth digital radio system. It was found that the effects of frequency selective fading result in unacceptably high system unavailability unless adaptive equalization and space diversity are employed. Specifically the results are: 1) Multipath induced outage is much higher than would be predicted from the measured flat fade margin of the equipment. For a nondiversity system, the probability of outage for a single hop in the worst fading month is approximately 1 \times 10^{-3} . This is 700 times the objective for a long haul system and corresponds to an effective fade margin of only 27 dB. 2) The primary cause of outage is inband distortion caused by the frequency selectivity of the multipath fading process. 3) Phase adaptive space diversity combining is very effective in reducing the amount of fading. In addition it affords some increase in the effective fade margin of the radio, i.e., it reduces the severity of inband distortion for a given fade depth. Outage for the System with space diversity combining was 2.6 \times 10^{-4} which is about 18 times the long haul objective. 4) A simple adaptive linear amplitude equalizer in conjunction with the phase adaptive space diversity combining provides an additional improvement of approximately a factor of 20, reducing the multipath outage to levels compatible with long haul availability objectives. 5) This same equalizer when applied to a non-diversity channel provides an improvement of about 2. Thus the preconditioning effect of phase adaptive space diversity combining is necessary to reduce distortions sufficiently that they can be dealt with by a relatively simple adaptive equalizer. These results apply to wideband digital radio which operates over long hops using a two dimensional modulation system such as QAM or multiphase PSK.

An Economical RC Active Equalizer with Applications in Communications

A simple active equalizer network employing two operational amplifiers (OA's), five resistors, and a pair of capacitors is presented. The same network can be used for both amplitude and delay equalizations. Experimental results show that the circuit can be conveniently used for amplitude equalization in voice communications, and for delay equalization in private line data circuits.

Minicomputers Improve Filter Testing at Western Electric

Minicomputers are used in controlling test equipment for process adjustments and final testing of complex passive filters and active amplitude equalizers. Automated testing reduces test time by factors of 5 : 1 which can yield a pay-back period of less than one year. These facilities can be used for adjusting and testing insertion loss or gain, return loss, current drain, continuity, and other active parameters. The operator interacts with the computer control through a simple keyboard terminal controlling the options available; i.e., data printout, adjustment or final test. Software is written at machine level to allow the use of 8K machines. The software includes a monitor and individual product programs. Each test facility uses an individual computer for its control center because it reduces software and hardware complexity.

An ultrasound receiver with programmable time gain control.

An ultrasound receiver with programmable time gain control (TGC) has been developed. The TCG curve is synthesized from sequentially gated analog switches, each of which controls receiver gain over a range of 1cm. Diagnostic studies using a receiver with the programmable TGC curve show improved results in the amplitude equalization of received echoes and in the output display.

On piecewise linear approximation of attenuation function with specified slope and range

A method of approximating attenuation functions by straight line segments whose slope and range can be chosen independently within certain bounds is described. Realization of the approximant is straightforward, and results in a simple, easily adjustable network. The maximum approximation error is calculated and can be made as small as desired. The method can be applied to adaptive amplitude equalizers.

Ripple-pass function

The well-known relation for an all-pass function is generalized by the introduction of two parameters <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_{a}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_{b}</tex> making <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F(s)=\frac{EvP(s)-k_{a}OdP(s)}{EvP(s)+k_{b}OdP(s)}</tex> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P(s)</tex> is a Hurwitz polynomial, while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EvP(s)</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OdP(s)</tex> are its even and odd parts, respectively. It is shown that the amplitude, phase, and group delay of such a generalized all-pass function ripple, and that the ripples are dependent on the two introduced parameters and their ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K = k_{a}/k_{b}</tex> . Thus the name "ripple-pass function." Some interesting and important features of the discussed function have been considered here. The ripple-pass function is suitable for practical applications such as amplitude, phase, and/or delay equalization, or for design of narrow-bandpass or bandstop (notch) filters. The ripple-pass function can be easily realized by using simple passive and active networks.

Mop-Up Equalization of Certian AM-PM Distortion Effects in FDM-FM Transmission Systems

In frequency division multiplexing (FDM)-FM transmission systems, unequalized parabolic delay preceding a component with AM-PM conversion can be an important source of intermodulation distortion. This correspondence describes some manifestations of these distortion effects and indicates how the distortion can be reduced with cubic IF amplitude equalizers applied on a mop-up basis.

Active Adjustable Loss and Delay Equalizers

The design of active amplitude and delay equalizers to be used in private line data systems is considered. These equalizers provide sufficient flexibility of adjustment so that one type of amplitude equalizer and one type of delay equalizer are sufficient for all applications. They replace families of passive equalizers which permitted relatively limited or no adjustment.

Active adjustable loss and delay equalizers

The design of active amplitude and delay equalizers to be used in private line data systems is considered. These equalizers provide sufficient flexibility of adjustment so that one type of amplitude equalizer and one type of delay equalizer are sufficient for all applications. They replace families of passive equalizers which permitted relatively limited or no adjustment.

Transversity-Amplitude Analysis of the ReactionsK−p→(ω,ϕ)Λ

We present a model-independent amplitude analysis of the reactions ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}(\ensuremath{\omega},\ensuremath{\phi})\ensuremath{\Lambda}$ using combined data at 3.9- and 4.6-GeV/c incident momenta. The joint correlations between the vector meson and the $\ensuremath{\Lambda}$ hyperon, in addition to the single density-matrix elements and the $\ensuremath{\Lambda}$ polarization, are observed and the magnitudes and four relative phases of the six independent transversity amplitudes which describe the reactions are determined. The amplitudes for ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\Lambda}$ are compared with results from a similar analysis of ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{*0}\ensuremath{\Lambda}$ and excellent agreement with the quark-model prediction of equality of the amplitudes is found. In addition, for the reaction ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\omega}\ensuremath{\Lambda}$ we make some model-dependent assumptions which allow the determination of the structure of the $s$-channel helicity amplitudes. These amplitudes are compared with duality predictions and implications concerning absorption prescriptions are discussed.

A Baseband Hybrid Digital Transmission Scheme

A baseband hybrid digital transmission scheme is studied, and it is shown that the low- and high-frequency cutoffs in analog repeaters extremely degrade signal waveforms. Solutions studied are a combination of dc-constrained coding and modification of amplitude-frequency characteristics for low-frequency distortion, and a combination of flat amplitude equalization and simple phase equalization for high-frequency distortion. It is shown that these solutions reduce waveform distortions by a factor of ten. A solution of the control problem for automatic gain control (AGC) is also presented.

Love waves in nonuniform wave guides: Finite difference calculations

A simple finite difference approximation to the elastic equations of motion is successfully used to solve various wave-propagation problems possessing analytical solutions. On this basis the method is extended to the problem of Love waves propagating across an ocean-continent type boundary. Numerical propagation of an initial transient solution results in seismograms at various distances. The Fourier transforms of these seismograms are used to calculate phase velocity, group delay, and amplitude-transfer coefficients for various seismometer combinations across the transition region. Some results are' the transition zone can have a small but noticeable effect on phase velocities measured between stations situated away from the zone; a phase-velocity anisotropy exists for waves propagating in opposite directions across the same array. In general, waves propagating into the region of thinning have anomalously high-phase velocities and vice versa. This is especially noticeable for velocities measured over the zone of transition, where the perturbations of the phase velocity of continent-to-ocean waves from the expected local phase velocity can exceed the variations expected from the continent-ocean structural differences. The behavior at a distance from the boundary justifies the well-established method of calculating effective group velocities by means of inverse averages of regional group velocities and also indicates a simple correction for the effect of the ocean-continent boundary that can be applied to calculations of earthquake-source mechanisms based on the method of amplitude equalization.

Elastic Unitarity and Phase Equality of Scattering Amplitudes

Elastic Unitarity and Phase Equality of Scattering Amplitudes

SHORT‐PERIOD SIGNAL PROCESSING RESULTS FOR THE LARGE APERTURE SEISMIC ARRAY

Processing of seismic data from LASA can be accomplished by simple delay and sum or beam forming, weighted delay and sum or by maximum‐likelihood filtering. It is found that band‐pass prefiltering the data has a considerable effect on the results. The extra gain produced by maximum likelihood filtering does not justify use of this process on‐line, but could justify off‐line processing in special cases. The spurious precursor introduced by maximum‐likehood processing, and shown to be caused primarily by the signal amplitude scatter within a subarray, can be effectively reduced by using amplitude equalization. The signal amplitude scatter within a subarray, and between subarrays, does not degrade seriously the performance of the signal processing. The effectiveness of the processing depends not only on the array spatial filtering ability, but on differences in absolute level of the noises in the various sensors. Our experience in processing a weak event whose apparent magnitude, as averaged over the LASA was 3.5, indicated that the maximum likelihood filter was capable of extracting the event from the background noise well enough that the event could be identified as an earthquake and not a nuclear explosion.

ELECTROENCEPHALOGRAPHIC AND CLINICAL SURVEY OF THE DEEP LEVEL TUMOR OF THE BRAIN

Comparing the EEG of normal individuals and of cases with superficial tumor of the brain, electroencephalographic survey in 79 cases of vertified deep cerebral and infratentorial tumor has been made.EEG abnormality responsible for deep tumors are composed of two signs, which appears in EEG tracing due to brain disease and appears in normal individuals with less severity and less frequency. If the former is denominated major sign, the latter will be minor sign. Major sign are consisted of 1) parasagittal homologous synchronous burst, 2) homologous bilaterally burst except parasagittal area, 3) shifting inter-hemispheric burst or burst like activity between homologous regions, 4) over all unihemispheric emphasis of wave amplitude decrease or voltage increase. Minor sign are 1) continuous or frequent bianterior amplitude predominance, 2) continuous or almost continuous appearance of anterior-posterior amplitude equalization, 3) low amplitude theta waves localized at bicentral region or the neighbouring area which appears much abandance comparing the normal persons.These signs are non specific, but significant manifestation of deep level disturbance. Only 79 cases are analyzed here and there is the paucity of the report dealt with minor signs. Therefore, further careful evaluation of these signs should be necessary.

Determination of source parameters by amplitude equalization of seismic surface waves: 2. Release of tectonic strain by underground nuclear explosions and mechanisms of earthquakes

The radiation patterns of Love and Rayleigh waves from three nuclear explosions (Hardhat, Haymaker, and Shoal) are studied to determine the nature of the asymmetry of radiation and the mechanism of Love wave generation. From a comparative study of different explosions it is reasoned that the Love waves are generated at the source of the explosion. The source function, represented as the superimposition of an isotropic dilatational component due to the explosion and a multipolar component due to the release of tectonic strain energy, is consistent with the observed radiation patterns and the amplitude spectrums. The amount of seismic energy due to the strain release is computed. In some cases (Haymaker and Shoal) it is found that this energy may be due to the relaxation of the pre-stressed medium by the explosion-formed cavity. In the case of Hardhat it is concluded that the explosion must have triggered some other strain release mechanism, such as an earthquake. The amplitude equalization method is applied to surface waves from an earthquake to determine the source parameters. From only the amplitude spectrums and radiation patterns of Love and Rayleigh waves, the source functions, source depth, strike and dip of the fault plane, and the rake of displacement are determined for the July 20, 1964, Fallon earthquake.