Transionospheric propagation of FM signals
Transionospheric propagation of FM signals for satellite communications
IONOSPHERIC PROPAGATION↗
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Results for “Frequency modulation”
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A compatible double sideband/single sideband/ constant bandwidth FM telemetry system for wideband data.
Compatible double sideband/single sideband/constant bandwidth FM telemetry system for wideband data
SIDEBAND↗
Principle and design of a Vernier FM radar system.
Signal design and principle of vernier FM radar system to measure surface characteristics of small target at long distance and range resolutions
FREQUENCY MODULATION↗
Discriminator response to an FM signal in a fading channel.
Discriminator threshold and SNR above threshold response when demodulating FM signal undergoing selective fading
SIGNAL TO NOISE RATIO↗
Frequency locked loop FM demodulator.
Frequency locked loop FM demodulator with high noise threshold
NOISE THRESHOLD↗
Development of low cost receiving systems for television signals transmitted from synchronous satellites
Satellite microwave receiver systems which convert carrier frequencies and modulation formats to produce signals compatible with VHF-UHF television receivers for low-cost service
Miller, E. F.↗
Reciprocal - MSE and SNR as distinct performance measures in below-threshold communication.
The possible advantages of using algorithms that are minimum mean-square-error (MSE) optimal, or other averaging-type demodulators with frequency position modulation (FPM), are investigated. An attempt is made to describe the performance of the optimal and various suboptimal demodulators in terms of three parameters which depend on SNR and bandwidth expansion. The performance measures investigated are the reciprocal of the normalized mean-square error and the output SNR, which are different in the below-threshold region. The former is compared to the rate-distortion bound. The possible advantage of averaging-type discriminators from the point of view of the threshold is discussed.
Bar-David, I.↗
High speed, high performance /Hg,Cd/Te photodiode detectors.
The current performance of high speed photodiode detectors for the 1 to 10 micron spectral region is discussed. The (Hg,Cd)Te photodiode configuration, detector properties, integration in laser receiver modules, and frequency response are considered for near infrared and far infrared wavelengths. The recent advances in (Hg,Cd)Te material and device development are indicated by the realization not only of exceptionally high speed detectors but of detectors that exhibit excellent detectivities. The performance improves substantially when the detector is cooled. This detector junction technology has been extended to other compositions of (Hg,Cd)Te for peak spectral responses at 5 and 10 micron.
Soderman, D. A.↗
Tracking and data relay satellite system configuration and tradeoff study, part 1. Volume 3: Telecommunications service system
The results of the telecommunications subsystem analysis are presented. The relay system requirements and constraints, interference analysis, frequency selection, modulation and coding analysis, and the performance analysis of the relay system are included.
Source record↗
Communication architecture for large geostationary platforms
Large platforms have been proposed for supporting multipurpose communication payloads to exploit economy of scale, reduce congestion in the geostationary orbit, provide interconnectivity between diverse earth stations, and obtain significant frequency reuse with large multibeam antennas. This paper addresses a specific system design, starting with traffic projections in the next two decades and discussing tradeoffs and design approaches for major components including: antennas, transponders, and switches. Other issues explored are selection of frequency bands, modulation, multiple access, switching methods, and techniques for servicing areas with nonuniform traffic demands. Three-major services are considered: a high-volume trunking system, a direct-to-user system, and a broadcast system for video distribution and similar functions. Estimates of payload weight and d.c. power requirements are presented. Other subjects treated are: considerations of equipment layout for servicing by an orbit transfer vehicle, mechanical stability requirements for the large antennas, and reliability aspects of the large number of transponders employed.
Bond, F. E.↗
Temperature controller for hyperthermia devices
Temperature controller monitors and controls temperature in local region of tumor. Medical grade thermocouples are inserted in or near tumor, controller pulse modulates radio frequency diathermy power source to maintain temperature within 0.2 C. System may be extended to control diathermy of more than one tumor or patient.
Couch, R. H.↗
RAWINPROC: Computer program for decommutating, interpreting, and interpolating Rawinsonde meteorological balloon sounding data
The FORTRAN computer program RAWINPROC accepts output from NASA Wallops computer program METPASS1; and produces input for NASA computer program 3.0.0700 (ECC-PRD). The three parts together form a software system for the completely automatic reduction of standard RAWINSONDE sounding data. RAWINPROC pre-edits the 0.1-second data, including time-of-day, azimuth, elevation, and sonde-modulated tone frequency, condenses the data according to successive dwells of the tone frequency, decommutates the condensed data into the proper channels (temperature, relative humidity, high and low references), determines the running baroswitch contact number and computes the associated pressure altitudes, and interpolates the data appropriate for input to ACC-PRD.
Staffanson, F. L.↗
Damping Relaxation Oscillations in Laser Diodes
Proposed semiconductor laser modulated at frequencies up to near its resonant frequency more efficiently than older devices. New laser uses two different effective carrier lifetimes: one for dc and lowfrequency operation and another for operation near resonant frequency. Laser part of bipolar transistor with capacitor that serves as ac short circuit.
Katz, J.↗
Evaluation and comparison of dominant backscattering sources at 10 GHz in two treatments of tall-grass prairie
A very-fine-range resolution Frequency Modulated-Continuous Wave radar, operating at X-band, was used to evaluate the primary backscattering contributors to the radar signal from a tall-grass prairie. Defoliation was used to help measure relative backscatter from various components of the canopy with both linear polarizations and at 30 deg and 50 deg incidence angles. Variation of the average returned power with incidence angle was greatest for the natural prairie at horizontal polarization and was the least for vertical polarization. Vertical polarization seemed to be more sensitive to the upper portions of the plants, whereas horizontal polarization was to the lower portions. Attenuation for horizontal polarization was only half that for vertical polarization. Dielectric measurements of the grass and some of the canopy components were conducted as well.
Zoughi, Reza↗
Ionospheric signatures of cusp latitude Pc 3 pulsations
Search coil magnetometer, riometer, photometer, and ELF-VLF receiver data obtained at South Pole Station and McMurdo, Antarctica during selected days in March and April 1986 are compared. Narrow-band magnetic pulsations in the Pc 3 period range are observed simultaneously at both stations in the dayside sector during times of low IMF cone angle, but are considerably stronger at South Pole, which is located at a latitude near the nominal foot point of the dayside cusp/cleft region. Pulsations in auroral light at 427.8 nm wavelength are often observed with magnetic pulsations at South Pole, but such optical pulsations are not observed at McMurdo. The observations suggest that precipitating magnetosheathlike electrons at nominal dayside cleft latitudes are at times modulated with frequencies similar to those of upstream waves. These particles may play an important role, via modification of ionospheric currents and conductivities, in the transmission of upstream wave signals into the magnetosphere and in the generation of dayside high-latitude Pc 3 pulsations.
Engebretson, M. J.↗
Multiple-Symbol Differential Detection Of MPSK
Multiple-symbol differential detection proposed for reception of radio-frequency signals modulated by mutliple-phase-shift keying (MPSK). Offers advantage of less complexity in not requiring equipment to acquire and track carrier signal. Performance approaches that of ideal coherent detection. Applicable to coded as well as uncoded MPSK, and to other forms of modulation.
Divsalar, Dariush↗
Designing Two Telemetry Channels With A Ranging Channel
Method of optimization devised for use in selecting frequencies, powers, modulation indices, and other parameters of two digital-data telemetry channels and coherent turnaround ranging channel of Earth-station/satellite communication system. Also applicable to design of terrestrial communication systems based on similar modulation schemes and present similar design problems.
Nguyen, Tien M.↗
Worldwide survey of direct-to-listener digital audio delivery systems development since WARC-1992
Each country was allocated frequency band(s) for direct-to-listener digital audio broadcasting at WARC-92. These allocations were near 1500, 2300, and 2600 MHz. In addition, some countries are encouraging the development of digital audio broadcasting services for terrestrial delivery only in the VHF bands (at frequencies from roughly 50 to 300 MHz) and in the medium-wave broadcasting band (AM band) (from roughly 0.5 to 1.7 MHz). The development activity increase was explosive. Current development, as of February 1993, as it is known to the author is summarized. The information given includes the following characteristics, as appropriate, for each planned system: coverage areas, audio quality, number of audio channels, delivery via satellite/terrestrial or both, carrier frequency bands, modulation methods, source coding, and channel coding. Most proponents claim that they will be operational in 3 or 4 years.
Messer, Dion D.↗