SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A high-sensitivity spectroscopic measurement of O2 using two-tone frequency modulation spectroscopy with a GaAlAs diode laser is presented. An oxygen sensor based on this technique would be non-intrusive, compact and possess high sensitivity and fast time response.
This paper describes an electrically passive fiber-optic interferometer which uses dual frequency-modulated laser diodes. Experimental results show that this type of interferometer can attain a displacement range of 100 micron with subnanometer resolution. This technique can serve as the basis for a number of high-precision fiber-optic sensors.
New type of correlation spectrometer eliminates need to shift between two cells, one empty and one containing reference gas. Electrooptical phase modulator sinusoidally shift frequencies of sample transmission spectrum.
Waveguide cavity CW Gunn microwave oscillator bias voltage controlled amplitude and frequency modulation
Results are presented of subjective and quantitative tests describing the results of interference to a particular digital television system from a frequency modulated (FM) television system, and for interference to an FM television system from a digital television system.
Analog modulation, frequency-division multiplexing and signal processing for multiple-access satellite communication
A method for detecting a target fluid in a fluid sample comprising a first fluid and the target fluid using photoacoustic spectroscopy (PAS), comprises a) providing a light source configured to introduce an optical signal having at least one wavelength into the fluid sample; b) modulating the optical signal at a desired modulation frequency such that the optical signal generates an acoustic signal in the fluid sample; c) measuring the acoustic signal in a resonant acoustic detector; and d) using the phase of the acoustic signal to detect the presence of the target fluid.
Shuttle Task 501 is an in-line task to test the performance and compatibility of radiofrequency links between the SSO and ground, and relay via a satellite. Under Shuttle Task 501 approach and landing test (ALT) phase only a limited portion of the communication and tracking (C&T) equipment is to be tested. The principal item to be tested is a frequency modulated (FM) data link. To test this RF link, an ALT FM System was designed, constructed, and the console wiring verified. A step-by-step procedure to be used to perform the ALT FM system is presented. The ALT FM system test is to be performed prior to delivery of the equipment to the Electronic Systems Test Laboratory (ESTL).
When laser beam passes through electron plasma its frequency shifts by amount proportional to plasma density. This density varies with modulating signal resulting in corresponding modulation of laser beam frequency. Necessary apparatus is relatively inexpensive since crystals are not required.
Design of high frequency dc-dc converter modules for power conditioning subsystems, and control system for operating ion engines in space environment
Time domain expression derived for frequency varying nonperiodic square wave in FDM and FM systems, using orthogonal functions to obtain frequency spectrum
As the data rates required for digitally encoded television are reduced, satellite systems employing the transmission of digitally encoded television will become attractive. It is likely that television transmitted in this format will be adjacent to or in the same frequency band as television transmissions in other modulation formats, so a knowledge of carrier to interference power ratios as a function of assessed picture quality will be required for frequency sharing between these different modulation formats. This paper presents the results of subjective and quantitative tests describing the results of interference to a particular digital television system from a frequency modulated (FM) television system, and for interference to an FM television system from a digital television system.
A coherent-optical time-of-flight range-finding technique is proposed which uses a simple inexpensive device. Target range is determined by modulating a laser diode's optical frequency and measuring the change in the phase of the light reflected back into the laser. Target velocity as well as range can be measured using this approach. The device is described, and experimental evidence is presented to show the feasibility of measuring distance with subcentimeter resolution over a 1.5-m range.
Optimization of receivers for demodulating FM SIGNAL corrupted by Gaussian noise, and solution to maximum likelihood equation
FM feedback system for lunar orbiter signal demodulation, discussing system composition and performance
A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.
Threshold extension device for improving operating performance of frequency modulatioin demodulators by eliminating click-type noise impulses
We present a scheme to phase-lock a 240 mW, 852 nm distributed Bragg reflector (DBR) laser to a fixed-frequency narrow-linewidth laser with a rapidly tunable frequency offset near 9 GHz. The phase-lock is accomplished by electronic feedback on the beatnote between the two lasers. The frequency offset can be swept 200 MHz in 300 us, limited by the feedback loop bandwidth, allowing for its use in complex cooling and state preparation schemes needed in atomic physics experiments. Here, we find that the phase-lock reduces the linewidth of the DBR laser below its natural linewidth of ~400 kHz to ~100 kHz