scholarly journals Techniques for Coping with Radio Frequency Interference

2001 ◽  
Vol 196 ◽  
pp. 279-287
Author(s):  
J. R. Fisher
Keyword(s):  
Adaptive Filters ◽  
Dynamic Range ◽  
High Dynamic Range ◽  
Spectrum Management ◽  
Low Noise ◽  
Radio Signals ◽  
Management Effort ◽  
Technical Solutions ◽  
Spurious Radiation

As a complement to spectrum management efforts by radio astronomers a number of observatories and research groups around the world have begun looking into technical solutions to the problem of separating weak cosmic radiation from man-made radio signals. Some of the technical research now getting underway includes: high dynamic range receivers, low-noise superconducting filters, passive digital filtering, adaptive filters, adaptive sidelobe nulling, multi-feed correlation of RFI, and various techniques for signal blanking.Increased technical support to spectrum management can also be provided in the form of accurate and statistically significant characterization of the radio environment, empirical and theoretical improvement of over-the-horizon propagation models, and timely measurements of spurious radiation falling in the protected radio astronomy bands.Finally, credibility of our spectrum management effort can only be maintained by making sure that local radiation under the control of our radio observatories is in compliance with the field strength limits of Recommendation ITU-R R.A.769. This requires sensitive radiation measurements and often shielding of digital equipment, microwave ovens, test equipment, local oscillators, etc.

High Speed Characterization of Pseudomorphic Hemt Structures Using a Very Low Noise Scintillation Detector

1993 ◽  
Vol 37 ◽  
pp. 145-151
Author(s):  
N. Loxley ◽  
S. Cockerton ◽  
B. K. Tanner
Keyword(s):  
Quality Assurance ◽  
Scintillation Detector ◽  
High Speed ◽  
Dynamic Range ◽  
High Dynamic Range ◽  
Low Noise ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Dynamic

AbstractWe show that a very low noise, high dynamic range scintillation detector has major advantages over conventional detectors for characterization of pseudomorphic HEMT structures by high resolution X-ray diffraction. We show that the reduced background enables a second modulation period to be detected, enabling the thickness and composition to be determined independently. Using a conventional X-ray generator and diffractometer we demonstrate that, in a single scan taking only 10 seconds, we are able to obtain sufficiently good data to provide quality assurance.

High-dynamic-range low-noise microwave amplifier

1970 ◽  
Vol 6 (7) ◽  
pp. 202
Author(s):  
J.R. Collard ◽  
A.R. Gobat
Keyword(s):  
Dynamic Range ◽  
High Dynamic Range ◽  
Low Noise ◽  
Microwave Amplifier ◽  
High Dynamic

scholarly journals Relative sky radiance from multi-exposure all-sky camera images

2021 ◽  
Vol 14 (3) ◽  
pp. 2201-2217
Author(s):  
Juan C. Antuña-Sánchez ◽  
Roberto Román ◽  
Victoria E. Cachorro ◽  
Carlos Toledano ◽  
César López ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Quality Criteria ◽  
High Dynamic Range ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
High Dynamic ◽  
Sky Radiance ◽  
Black Level ◽  
Hdr Image

Abstract. All-sky cameras are frequently used to detect cloud cover; however, this work explores the use of these instruments for the more complex purpose of extracting relative sky radiances. An all-sky camera (SONA202-NF model) with three colour filters narrower than usual for this kind of cameras is configured to capture raw images at seven exposure times. A detailed camera characterization of the black level, readout noise, hot pixels and linear response is carried out. A methodology is proposed to obtain a linear high dynamic range (HDR) image and its uncertainty, which represents the relative sky radiance (in arbitrary units) maps at three effective wavelengths. The relative sky radiances are extracted from these maps and normalized by dividing every radiance of one channel by the sum of all radiances at this channel. Then, the normalized radiances are compared with the sky radiance measured at different sky points by a sun and sky photometer belonging to the Aerosol Robotic Network (AERONET). The camera radiances correlate with photometer ones except for scattering angles below 10∘, which is probably due to some light reflections on the fisheye lens and camera dome. Camera and photometer wavelengths are not coincident; hence, camera radiances are also compared with sky radiances simulated by a radiative transfer model at the same camera effective wavelengths. This comparison reveals an uncertainty on the normalized camera radiances of about 3.3 %, 4.3 % and 5.3 % for 467, 536 and 605 nm, respectively, if specific quality criteria are applied.

A low-noise and flexible FPGA-based binary signal measurement generator

2019 ◽  
Vol 11 (5-6) ◽  
pp. 447-455 ◽  
Author(s):  
Gordon Notzon ◽  
Robert Storch ◽  
Thomas Musch ◽  
Michael Vogt
Keyword(s):  
Dynamic Range ◽  
Time Lag ◽  
Impulse Response Function ◽  
High Dynamic Range ◽  
Noise Signal ◽  
Low Noise ◽  
Ultra Wideband ◽  
Coded Excitation ◽  
Field Programmable ◽  
Noise Measurements

AbstractIn the area of electromagnetic metrology, binary coded excitation signals become more and more important and various binary coded sequences are available. The measurement approach is to assess the impulse response function of a device under test by correlating the response signal with the excitation signal. In order to achieve a high measurement reproducibility as well as a high dynamic range, the generated binary coded signals have to provide low-noise. In this contribution, a low-noise signal generator realized with a field programmable gate array is presented. The performance investigation of different kinds of binary coded excitation signals and different correlation concepts have been practically investigated. With a chip rate of 5 Gchip/s, the generator can be utilized for ultra-wideband applications. In order to allow for a low-noise and long-term stable signal generation, a new clock generator concept is presented and results of phase noise measurements are shown. Furthermore, an algorithm to fast and precisely shifting the time lag between two binary coded signals for correlating excitation and response signals with a hardware correlator is presented. Finally, the realized demonstrator system is tested using two commonly used types of binary coded sequences.

scholarly journals Electronic Optical Sky Surveys

1998 ◽  
Vol 179 ◽  
pp. 49-55
Author(s):  
T.A. McKay
Keyword(s):  
Dynamic Range ◽  
Large Fraction ◽  
High Sensitivity ◽  
High Dynamic Range ◽  
Low Noise ◽  
Computer Hardware ◽  
Optical Detectors ◽  
Small Fields ◽  
Technical Advances ◽  
High Dynamic

The introduction of of Charge Coupled Devices (CCDs) in the middle 1970s provided astronomy with nearly perfect (linear, high-sensitivity, low-noise, high dynamic-range, digital) optical detectors. Unfortunately, restrictions imposed by CCD production and cost has typically limited their use to observations of relatively small fields. Recently a combination of technical advances have made practical the application of CCDs to survey science. CCD mosaic cameras, which help overcome the size restrictions imposed by CCD manufacture, allow electronic access to a larger fraction of the available focal plane. Multi-fiber spectrographs, which couple the low-noise, high QE performance of CCDs with the ability to observe spectra for many objects at once, have improved the spectroscopic efficiency of telescopes by factors approaching half a million. An improved understanding of image distortion gives us telescopes on which we expect sub-arcsecond images a large fraction of the time. Finally, and perhaps most important, the performance of computer hardware continues to advance, to the point where analysis of multi-terabyte datasets, while still daunting, is at least conceivable.

Airborne TEM surveying with a SQUID magnetometer sensor

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 468-477 ◽  
Author(s):  
James B. Lee ◽  
David L. Dart ◽  
Robert J. Turner ◽  
Mark A. Downey ◽  
Arthur Maddever ◽  
...  
Keyword(s):  
Dynamic Range ◽  
High Dynamic Range ◽  
Performance Measure ◽  
Low Noise ◽  
Induction Coil ◽  
Squid Magnetometer ◽  
Superior Performance ◽  
Frequency Noise ◽  
High Dynamic ◽  
Squid System

Traditionally airborne time-domain electromagnetic (AEM) survey systems use induction coils as the sensor (receiver). We have replaced the induction coil in a transient electromagnetic (TEM) system with a liquid-nitrogen cooled superconducting quantum interference device (SQUID) magnetometer sensor. Using this prototype system, we aimed to improve performance in detecting conductive mineralization, particularly where the conductive mineralization of interest is covered by a conductive regolith. We successfully demonstrated one- and three-component SQUID sensors in airborne TEM surveying, and achieved performance comparable to the induction-coil systems. Implementation of the SQUID system required development of devices capable of operating in magnetically unshielded environments with low noise, high slew rate, and wide bandwidth. Operation of the SQUID sensor in the highly dynamic environment of a towed bird was also necessary, and this implies a high dynamic range and high level of noise associated with the motion in Earth's magnetic field. The high dynamic range of the SQUID response was handled by a combination of resetting the SQUID flux locked loop, reducing the bandwidth, and providing high-gain feedback in parallel with the flux locked loop. A digital stacking filter was used to eliminate low-frequency noise associated with sensor motion. Isolation of the sensor from motion at the TEM signal frequencies required development of a sophisticated suspension system. The SQUID systems were tested over two known conductive targets, and their performance compared with the induction-coil TEM system. A comparative performance measure is developed to take the different sensitivities of the SQUID magnetometer and induction-coil receivers into account. This measure indicates that the SQUID system has superior performance for responses over earth structures with decay time constants greater than ∼6 ms when compared with the induction-coil signals. We also estimate the performance in comparison with integrated outputs of the induction-coil system and show that, at the demonstrated levels of SQUID performance, it is expected to have poorer performance by a factor of two or more. This disadvantage will be reduced for lower frequency, wider channel width TEM configurations or by improvements in the SQUID devices.

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