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NASA NTRS1992

Windshear radar calibration: Transmitter power and receiver gain stability

An experimental windshear Doppler radar was flown on 27 occasions during a series of flight experiments in 1991. Radar calibrations were performed by the flight team to monitor the transmitter power and receiver gain from pre-flight to post-flight and from one day to another. From the recorded calibration data, the receiver gain and effective receiver system noise were calculated and tabulated, together with the transmitter power. These quantities of interest are compared for two receiver/transmitter (R/T) units and two intermediate frequency (IF) bandwidths that were tested in various modes. It was found that, in most operating modes, gain stayed within a 2.5-dB range and transmitter power stayed within a 20-watt range. R/T number 1 had 0.8 dB more gain and 1.2 dBm less noise power than R/T number 2. The 7-MHz IF bandwidth resulted in 1 dB more gain and 1 dBm less noise than the 2-MHz IF bandwidth. Depending on the R/T unit and IF bandwidth, the effective system noise power averaged between -107.3 dBm and -109.5 dBm.

Mackenzie, Anne I.↗

NASA NTRS1991

Gain and energy storage in holmium YLF

It is demonstrated that Q-switched holmium lasers are capable of high-gain and high-energy operation at 300 K. Small-signal gain coefficients of 0.50 and 0.12/cm have been measured in YLF and YAG, respectively. Small-signal gains of 0.50/cm are comparable to those achievable in Nd:YAG and are not typical of low-gain materials. This large gain in the Ho:YLF material is made possible by operating the amplifier in the ground state depletion mode. The amplifier performance data and associated analysis presented demonstrate that efficient energy storage is possible with very high excited state ion densities of the Ho 5I7 upper laser level. This is an important result since upconversion can limit the 5I7 population. Although upconversion was still present in this experiment, it was possible to achieve efficient energy storage, demonstrating that the problem is manageable even at high excitation densities in YLF.

Storm, Mark E.↗

NASA NTRS1993

Windshear radar calibration, 1992 flights: Transmitter power and receiver gain stability

During the 1992 NASA airborne Doppler windshear radar flights, radar calibrations were performed prior to each flight in order to determine transmitter power, receiver gain, and receiver noise power. The calibration results show that the average transmitter power in radar mode 6 was 186 watts, with a standard deviation of 7 watts. The average high power amplifier gain was 9.62 dB. At the wide IF bandwidth setting, the receiver gain was 123.1 dB, while at the narrow IF bandwidth setting, the gain was 121.8 dB. The receiver system noise as seen at the receiver input was -107.0 dBmw using the wide IF bandwidth and -107.9 dBmw using the narrow IF bandwidth. In radar mode 7, the receiver gain was the same as in mode 6. However, the receiver noise in mode 7 was about 2.5 dB less using the wide IF bandwidth and 2.0 dB less using the narrow IF bandwidth. The R/T unit flown in 1992 had also been flown the previous year when it produced comparable results. This technical memorandum was written as a follow-up to NASA TM-107589 (June 1992), which describes similar radar calibrations performed during the 1991 windshear radar flight experiments.

Mackenzie, Anne I.↗

NASA NTRS1999

The Performance Capabillities and Limitations of Gain-Limitated Propulsion Systems

Omniplanetary space flight requires new high-performance propulsion systems based on nuclear energy. Over the last several decades, many propulsion concepts have been discussed which will allow one-month missions to Mars and one-year missions to the outer planets. Such missions entail large mission velocities and vehicle accelerations, which in turn require both high exhaust velocities (and therefore, and extremely low mass-power ratios. High performance electric propulsion appears capable of enabling multi-month transits to Mars and the near-earth asteroids; however, the mass-power ratio of these systems appears too high to achieve large accelerations for outer planet missions. This presentation analyzed the round-trip mission times and distances. This analysis has shown that even high-performance power-limited systems cannot achieve the higher accelerations needed to meet fast missions to the outer planets. Gain-limited missions are necessary for those extremely aggressive missions. An analysis of spacecraft power systems via a power balance and examination of gain vs mass-power ratio has shown: (1) A minimum gain is needed to have enough power for thrust production and driver operation; (2) Increases in gain result in decreases in mass-power ratio, which in turn leads to greater achievable accelerations. However, there is an absolute minimum mass-power ratio for a given set of subsystems, even in the limit of infinite gain.

Schmidt, G. R.↗

NASA NTRS2000

Impact of Energy Gain and Subsystem Characteristics on Fusion Propulsion Performance Balances

Rapid transportation of large payloads and human crews to destinations throughout the solar system will require propulsion systems having not only very high exhaust velocities (I (sub sp) greater than or equal to 10 (exp 4) to 10 (exp 5) sec) but also extremely low mass-power ratios (alpha less than or equal to 10 (exp -1) kg/kW). Such low a are difficult to achieve with power-limited propulsion systems. but may be attainable with fusion and other high I (sub SP) nuclear concepts that produce energy within the propellant. The magnitude of this energy gain is of fundamental importance. It must be large enough to sustain the nuclear process while still providing a high jet power relative to the massive power-intensive subsystems associated with these types of concepts. This paper evaluates the energy gain and mass-power characteristics required for a consistent with 1-year roundtrip planetary missions ranging up to 100 AU. Central to this analysis is an equation for overall system a, which is derived from the power balance of a generalized "gain-limited" propulsion system. Results show that the gain required to achieve alpha approximately 10 (exp -1) kg/kW with foreseeable subsystem technology can vary from 50 to as high as 10,000, which is 2 to 5 orders of magnitude greater than current state-of-the art. However, order of magnitude improvements in propulsion subsystem mass and efficiency could reduce gain requirements to 10 to 1,000 - still a very challenging goal.

Chakrabarti, Suman↗

NASA NTRS1997

Visual signal detection in structured backgrounds. II. Effects of contrast gain control, background variations, and white noise

Studies of visual detection of a signal superimposed on one of two identical backgrounds show performance degradation when the background has high contrast and is similar in spatial frequency and/or orientation to the signal. To account for this finding, models include a contrast gain control mechanism that pools activity across spatial frequency, orientation and space to inhibit (divisively) the response of the receptor sensitive to the signal. In tasks in which the observer has to detect a known signal added to one of M different backgrounds grounds due to added visual noise, the main sources of degradation are the stochastic noise in the image and the suboptimal visual processing. We investigate how these two sources of degradation (contrast gain control and variations in the background) interact in a task in which the signal is embedded in one of M locations in a complex spatially varying background (structured background). We use backgrounds extracted from patient digital medical images. To isolate effects of the fixed deterministic background (the contrast gain control) from the effects of the background variations, we conduct detection experiments with three different background conditions: (1) uniform background, (2) a repeated sample of structured background, and (3) different samples of structured background. Results show that human visual detection degrades from the uniform background condition to the repeated background condition and degrades even further in the different backgrounds condition. These results suggest that both the contrast gain control mechanism and the background random variations degrade human performance in detection of a signal in a complex, spatially varying background. A filter model and added white noise are used to generate estimates of sampling efficiencies, an equivalent internal noise, an equivalent contrast-gain-control-induced noise, and an equivalent noise due to the variations in the structured background.

NASA Discipline Space Human Factors↗

NASA NTRS1998

Adaptive gain and filtering circuit for a sound reproduction system

Adaptive compressive gain and level dependent spectral shaping circuitry for a hearing aid include a microphone to produce an input signal and a plurality of channels connected to a common circuit output. Each channel has a preset frequency response. Each channel includes a filter with a preset frequency response to receive the input signal and to produce a filtered signal, a channel amplifier to amplify the filtered signal to produce a channel output signal, a threshold register to establish a channel threshold level, and a gain circuit. The gain circuit increases the gain of the channel amplifier when the channel output signal falls below the channel threshold level and decreases the gain of the channel amplifier when the channel output signal rises above the channel threshold level. A transducer produces sound in response to the signal passed by the common circuit output.

Engebretson, A. Maynard↗

NASA NTRS1998

Adaptive gain and filtering circuit for a sound reproduction system

Engebretson, A. Maynard↗

NASA NTRS2012

On-Wafer Measurement of a Multi-Stage MMIC Amplifier with 10 dB of Gain at 475 GHz

JPL has measured and calibrated a WR2.2 waveguide wafer probe from GGB Industries in order to allow for measurement of circuits in the 325-500 GHz range. Circuits were measured, and one of the circuits exhibited 10 dB of gain at 475 GHz. The MMIC circuit was fabricated at Northrop Grumman Corp. (NGC) as part of a NASA Innovative Partnerships Program, using NGC s 35-nm-gatelength InP HEMT process technology. The chip utilizes three stages of HEMT amplifiers, each having two gate fingers of 10 m in width. The circuits use grounded coplanar waveguide topology on a 50- m-thick substrate with through substrate vias. Broadband matching is achieved with coplanar waveguide transmission lines, on-chip capacitors, and open stubs. When tested with wafer probing, the chip exhibited 10 dB of gain at 475 GHz, with over 9 dB of gain from 445-490 GHz. Low-noise amplifiers in the 400-500 GHz range are useful for astrophysics receivers and earth science remote sensing instruments. In particular, molecular lines in the 400-500 GHz range include the CO 4-3 line at 460 GHz, and the CI fine structure line at 492 GHz. Future astrophysics heterodyne instruments could make use of high-gain, low-noise amplifiers such as the one described here. In addition, earth science remote sensing instruments could also make use of low-noise receivers with MMIC amplifier front ends. Present receiver technology typically employs mixers for frequency down-conversion in the 400-500 GHz band. Commercially available mixers have typical conversion loss in the range of 7-10 dB with noise figure of 1,000 K. A low-noise amplifier placed in front of such a mixer would have 10 dB of gain and lower noise figure, particularly if cooled to low temperature. Future work will involve measuring the noise figure of this amplifier.

Samoska, Lorene A.↗

NASA NTRS2014

Multimodal Pilot Behavior in Multi-Axis Tracking Tasks with Time-Varying Motion Cueing Gains

In a large number of motion-base simulators, adaptive motion filters are utilized to maximize the use of the available motion envelope of the motion system. However, not much is known about how the time-varying characteristics of such adaptive filters affect pilots when performing manual aircraft control. This paper presents the results of a study investigating the effects of time-varying motion filter gains on pilot control behavior and performance. An experiment was performed in a motion-base simulator where participants performed a simultaneous roll and pitch tracking task, while the roll and/or pitch motion filter gains changed over time. Results indicate that performance increases over time with increasing motion gains. This increase is a result of a time-varying adaptation of pilots' equalization dynamics, characterized by increased visual and motion response gains and decreased visual lead time constants. Opposite trends are found for decreasing motion filter gains. Even though the trends in both controlled axes are found to be largely the same, effects are less significant in roll. In addition, results indicate minor cross-coupling effects between pitch and roll, where a cueing variation in one axis affects the behavior adopted in the other axis.

motion simulators↗

NASA NTRS2011

Calibrated Noise Measurements with Induced Receiver Gain Fluctuations

The lack of well-developed techniques for modeling changing statistical moments in our observations has stymied the application of stochastic process theory in science and engineering. These limitations were encountered when modeling the performance of radiometer calibration architectures and algorithms in the presence of non stationary receiver fluctuations. Analyses of measured signals have traditionally been limited to a single measurement series. Whereas in a radiometer that samples a set of noise references, the data collection can be treated as an ensemble set of measurements of the receiver state. Noise Assisted Data Analysis is a growing field of study with significant potential for aiding the understanding and modeling of non stationary processes. Typically, NADA entails adding noise to a signal to produce an ensemble set on which statistical analysis is performed. Alternatively as in radiometric measurements, mixing a signal with calibrated noise provides, through the calibration process, the means to detect deviations from the stationary assumption and thereby a measurement tool to characterize the signal's non stationary properties. Data sets comprised of calibrated noise measurements have been limited to those collected with naturally occurring fluctuations in the radiometer receiver. To examine the application of NADA using calibrated noise, a Receiver Gain Modulation Circuit (RGMC) was designed and built to modulate the gain of a radiometer receiver using an external signal. In 2010, an RGMC was installed and operated at the National Institute of Standards and Techniques (NIST) using their Noise Figure Radiometer (NFRad) and national standard noise references. The data collected is the first known set of calibrated noise measurements from a receiver with an externally modulated gain. As an initial step, sinusoidal and step-function signals were used to modulate the receiver gain, to evaluate the circuit characteristics and to study the performance of a variety of calibration algorithms. The receiver noise temperature and time-bandwidth product of the NFRad are calculated from the data. Statistical analysis using temporal-dependent calibration algorithms reveals that the natural occurring fluctuations in the receiver are stationary over long intervals (100s of seconds); however the receiver exhibits local non stationarity over the interval over which one set of reference measurements are collected. A variety of calibration algorithms have been applied to the data to assess algorithms' performance with the gain fluctuation signals. This presentation will describe the RGMC, experiment design and a comparative analysis of calibration algorithms.

Racette, Paul↗

NASA NTRS2018

Multi-Parameter Nonlinear Gain Correction of X-Ray Transition Edge Sensors for the X-Ray Integral Field Unit

With its array of 3840 Transition Edge Sensors (TESs), the Athena X-ray Integral Field Unit (X-IFU) will provide spatially resolved high-resolution spectroscopy (2.5 eV up to 7 keV) from 0.2 to 12 keV, with an absolute energy scale accuracy of 0.4 eV. Slight changes in the TES operating environment can cause significant variations in its energy response function, which may result in systematic errors in the absolute energy scale. We plan to monitor such changes at pixel level via onboard X-ray calibration sources and correct the energy scale accordingly using a linear or quadratic interpolation of gain curves obtained during ground calibration. However, this may not be sufficient to meet the 0.4 eV accuracy required for the XIFU. In this contribution, we introduce a newtwo-parameter gain correction technique, based on both the pulse-height estimate of a fiducial line and the baseline value of the pixels. Using gain functions that simulate ground calibration data, we show that this technique can accurately correct deviations in detector gain due to changes in TES operating conditions such as heat sink temperature, bias voltage, thermal radiation loading and linear amplifier gain. We also address potential optimisations of the onboard calibration source and compare the performance of this new technique with those previously used.

Cucchetti, E.↗

NASA NTRS2018

The ISARA Mission – Flight Demonstration of a High Gain Ka-Band Antenna for 100Mbps Telecom

The NASA sponsored ISARA (Integrated Solar Array and Reflectarray Antenna) mission successfully demonstrated a 100 Mbps Ka-band CubeSat communications capability. The enabling technology is a high gain reflectarray antenna integrated into a modified Pumpkin “Turkey Tail” solar array which wraps around the spacecraft body, essentially requiring near zero volume to accommodate. A simple low gain feed is used to distribute RF power to the reflectarray through free space. The 0.5kg ISARA antenna mass is compatible with the requirements of a 3U (10x10x10 cm3) spacecraft. The ISARA mission validated this approach in a flight technology demonstration. A unique on-orbit measurement system provided accurate measurement of the antenna gain from space. This system demonstrated 100Mbps downlink data rate capability using a relatively simple ground station with a 70cm parabolic reflector antenna. The spacecraft also verified ISARA solar panel output power and demonstrated the operational capability to accurately point the antenna to a Ka-band ground station, a key requirement for a telecom system. ISARA achieved a number of technological firsts. It is believed to be the first reflectarray antenna flown in space, first high gain antenna integrated with solar panels, first calibrated reflectarray antenna gain and pattern measurement performed from space and the first 3U CubeSat to demonstrate 100 Mbps using a small, low-cost ground station.

Martin, Jerami M.↗

NASA NTRS2002

Error margin for antenna gain measurements

The specification of measured antenna gain is incomplete without knowing the error of the measurement. Also, unless gain is measured many times for a single antenna or over many identical antennas, the uncertainty or error in a single measurement is only an estimate. In this paper, we will examine in detail a typical error budget for common antenna gain measurements. We will also compute the gain uncertainty for a specific UHF horn test that was recently performed on the Jet Propulsion Laboratory (JPL) antenna range. The paper concludes with comments on these results and how they compare with the 'unofficial' JPL range standard of +/- ?.

error antennas gain↗

NASA NTRS2019

Defining and Measuring Pressure Gain

This presentation describes experimental and computational approaches to measuring pressure gain in the various devices currently under investigation wherein the working fluid undergoes a pressure gain combustion (PGC) process. Pressure gain is essentially a measure of the fluid availability for work or thrust production. The devices covered are Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines. The approaches to pressure gain measurement differ in each device. However, all of the approaches attempt to address the fundamental challenges of PGC system measurement: the extremely harsh environment which makes instrumentation difficult, and the temporal and spatial non-uniformity associated with the exhausting flow which makes assigning a single value to the total pressure difficult. As part of the two-day 2019 International Constant Volume and Detonative Combustion Workshop, held in conjunction with the 2019 AIAA Propulsion and Energy Forum, this presentation is intended to foster discussion and eventual consensus on acceptable measurement methods.

pressure gain combustion↗

NASA NTRS1972

Anisotropic ultrahigh gain emission observed in rotational transitions in optically pumped HF gas.

Gain and laser oscillations are obtained on rotational transitions of the first excited vibrational state of HF gas at room temperature, resonantly pumped by the 2.7-micron lines of a pulsed HF laser. Pumping the P-branch transitions connecting the ground and first excited vibrational states produces gain at the coupled rotational transitions at 36, 42, 51, 63, 84, and 126 microns. The gain exhibits directional properties characteristic of a unidirectional amplifier predicted by a recent theory. The incremental gains of these lines are very large, in excess of 1/cm, and the lines oscillate easily without mirrors (superradiance).

Skribanowitz, N.↗

NASA NTRS1977

On the maximum off-axis gain of symmetrical pencil-beam antennas

For a general class of symmetrical pencil-beam antennas, the gain at a given off-axis angle can be maximized by choosing the proper antenna size. The maximum gain at the given angle relative to the on-axis gain is independent of the given angle and dependent only on the main-beam pattern. It is computed here for four commonly used gain functions. Its value, in all cases, is close to 4 dB. This result is important in the definition of service areas for communication and broadcast satellites.

Sawitz, P. H.↗

NASA NTRS1977

Small-signal gain diagnostic measurements in a flowing CO2 pin discharge laser

Small-signal gain diagnostic measurements were conducted on closed loop, high power, carbon dioxide laser to assess the coupling between gas flow velocity and resonator saturation. Parameters investigated included optical cavity and discharge power. Results of gain measurements within and downstream of the excitation volume are presented for a laser gas composition He:N2:CO2 of 10:7:1 at 90 torr. The gain at constant discharge power was observed to be dependent upon discharge power level and time. An important result of this study is that the effects of gain swept downstream of the discharge region must be considered in the resonator design if efficient extraction of stored optical energy is desired.

Blech, R. A.↗