Atomic Physics for Atmospheric Composition Measurements

The atomic physics relevant to the interpretation of solar spectra produced by plasmas at temperatures ≳ 105 K are discussed. Methods for determining relative abundance ratios are presented and examples provided from the Coronal Diagnostic Spectrometer on board SOHO. In particular, the Fe/Si ratio in the corona is found to be close to photospheric; the Mg/Ne ratio in the transition region is found to vary by an order of magnitude in different solar features. The Mg/Ne ratios in supergranule cell centres and the network are separated for the first time, although no significant differences are found. This revised version was published online in June 2006 with corrections to the Cover Date.     

Wide Dynamic Range Preselectors

Crowding of the Military communication spectrum has aggravated the need for preselectors capable of receiving a low-level desired signal in the presence of a high-level adjacent channel signal. Described herein are two novel HF preselection approaches which appear eminently suitable to cope with this problem. Applicable to the frequency range of 2 to 30 Mc/s, one preselector employs parametric mixing and the other exploits the low loss properties of superconductivity. In addition to other advantageous features, both preselectors have demonstrated an outstanding dynamic range capability in the order of 140 dB. Each of the preselectors is evaluated as a conventiona1 filter. In addition, performance data of a high quality military receiver is compared with that obtained when the receiver is preceded by each of two preselectors. Considerable stress is placed on the use of crossmodulation characteristics as a more meaningful and precise measure of preselector performance.     

Automatic Electronic Switching for a Field Army

A family of 4-wire electronic equipments is being developed for use in a tactical switching system for the field army. The characteristics and design of two automatic switchboards to be used in the system are discussed, as well as the signaling methods and numbering plan that are employed.     

Statistical Measurements of Phase-Locked Receivers

Test instrumentation is described for use in the measurement of threshold sensitivities and noise bandwidths of narrow-band phase-locked receivers. The method is statistical in nature with the data being recorded digitally by a counter and printer. Scale factors can be selected for convenient relation of the data to the standard deviations, 1,2, or 3 sigma. Curves are included showing the results of a typical experiment.     

Cancellation of Unwanted Spectral Components in an FM Multivibrator System

The performance of FM multivibrator systems for high quality communications applications is limited by the presence of unwanted spectral components. A theory is presented for an improved system in which unwanted spectral components are cancelled, achieved by generating a cancelling component in a square-law device. The cancelling component tracks the unwanted component in both frequency and amplitude over a wide bandwidth of signal frequencies. Reductions in magnitude of the unwanted components by at least 16 dB are predicted; reductions of better than 14 dB have been achieved in practice.     

Proposal Perfidy, A Poverty Syndrome (Ethics as a Prerequisite to Proposal Success)

There is a direct correlation between proposal success and proposal ethics, a fact which is independent of the proposal scope or the type of customer. To be successful, a proposal must result in a profit when measured within the total environment of present and future sales. A misleading or unethical proposal has little chance of leading to an immediate contract, is most likely to incur cost penalties if a contract does result, and is certain to reduce the probabilities for future sales. Unfortunately proposals tend to deal in that gray area between fact and fiction; the normal desire to present things in their most favorable light leads to misrepresentation. In his own professional interests the proposal engineer must learn to give an honest and accurate portrayal of his plan and his product.     

Optimum Processing of Unequally Spaced Radar Pulse Trains for Clutter Rejection

A train of radar pulses from one resolution cell can be processed coherently to reject echoes from external clutter and detect targets moving radially with respect to the clutter. Optimum methods of signal processing are defined for systems in which the interpulse spacings are multiply staggered to avoid target blind speeds. Likelihood ratio tests are developed for systems in which the target Doppler frequency is known a priori and for systems employing a bank of filters to cover the target Doppler band. To implement such tests, the N pulses in the train are added with complex weights and the amplitude of the sum compared with a detection threshold. The set of weights which maximizes the average signal-to-clutter ratio is also computed for a single-filter system with unknown target Doppler frequency. When the clutter autocorrelation function is exponential, the clutter covariance matrix can be inverted analytically. This latter result is useful for comparing different interpulse-spacing codes for a particular system application.     

System Design for Improved Extra-Terrestrial Communications

This paper describes a proposed system for improved exo-ionospheric communications. The dynamic magneto-ionic character of the channel is considered, in particular, the multipath situation arising therefrom. An ideal matched filter is found, matched to the multipath structure and the dynamics of the exo-ionospheric channel. The improvement in the signal-to-noise ratio through the matched filter is calculated. It is seen to depend on the quotient of the input signal to the bandwidths of the ``measuring' filter and the ``integrating' filter. Further advantages are shown to accrue from signal processing at the transmitter involving both increases in range, and, in particular, secure coding possibilities.