Systems & Subsystems
 82 results found for Systems & Subsystems, displaying items 41 - 60

December 2006
Chilean Antenna Array Reaches Deep Across Space
Millimeter-Wave Frequencies are sometimes associated with military missile guidance systems and commercial automotive radars. They are also essential to radio astronomy, including the world’s most advanced millimeter/submillimeter wavelength radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA). The giant array is under construction high in the Chilean Andes Mountains as part of an international project to design, build, and operate a multi-element...  — Dr. Andrew Clegg

November 2006
ACM Controls Cost Of Increased Spectral Efficiency
Cellular-communications system operators depend on efficient access network technologies to maximum spectral efficiency (bits/Hz) at minimum cost. Adaptive code and modulation (ACM) is an emerging wireless technology-that promises to do just that. With ACM technology, cellular operators can provide high-capacity payload over microwave links and improve the link utilization; this lowers capital expenditures for the RF equipment and operational expenditures for the...  — Ran Soffer

October 2006
Develop Advanced Designs For RFID Transponders
Radio-frequency identification (RFID) transponder design techniques were introduced last month, in the opening installment of this two-part article series. This month more advanced methods will be explored for enhancing the performance of UHF RFID transponders, using four design examples in Germany, the United States, Italy, and Switzerland. The German group was involved in pioneering work in UHF RFID, developing a variety of efficient circuit design techniques. However,...  — Faisal Mohd-Yasin , et al.

October 2006
Spread-Spectrum Modules Communicate At 2.4 GHz
Spread-spectrum technology was developed during World War II for the military, as a means of providing secure and reliable communications even in hostile environments. By 1980, the technology was approved by the FCC for use in industrial, scientific, and medical wireless applications in addition to military. The technology is now used for mission-critical and life-saving applications. There are a number of proprietary protocols and the standards-based protocols including...  — Jack Browne

September 2006
Frequency Synthesizers Supply Stable Signals
Frequency synthesizers generate the stable, low-noise signals for many microwave designs, including commercial communications systems, electronic warfare and intelligence systems, and test equipment. Synthesizers come in many shapes and sizes, from tiny integrated circuits (ICs) to modular systems in rugged rack-mount enclosures, and in many technologies, from direct and indirect analog types of fast-switching direct-digital synthesizers (DDS). Because of the breadth ...  — Jack Browne

September 2006
Technology Cancels Cellular Interferenc
Interference often stands in the way of effective communications. In third-generation (3G) wireless-communications systems, interference can degrade the quality of service (QoS), decrease efficiency, and bring the data rates of digital communications networks to a crawl. Fortunately, a company called TensorComm (Westminster, CO, www.tensorcomm.com) has developed an innovative technique for dealing with interference...  — Jack Browne

August 2006
Signal Cancellation Improves DDS SFDR
Direct digital synthesizers (DDS) are commonly used for sinusoidal signal generation in RF communication systems and test equipment. An integral component of DDS is the digital-to-analog converter (DAC). Although a DAC is intended to perfectly reproduce an analog signal from its digital equivalent, the conversion process is rarely perfect. The DAC's digital resolution (number of bits) is a limiting factor that introduces quantization errors resulting in a noise floor. ...  — Ken Gentile , et al.

August 2006
Optical Switches Link Multiple Receivers To Remote Antennas
Optical fiber provides many undisputed benefits for data-transmission systems. It also offers significant performance advantages in RF transmission systems, in spite of the fact that RF engineers have mistakenly considered fiber-optic cables to have lower dynamic range and higher costs than metal coaxial cables. Because of these beliefs, optical fiber has been limited to RF applications where long-distance transmissions have been beyond the capabilities of coaxial ...  — Bruce Mead

May 2006
Low-Power Approach Provides QPSK Modulation
Quadrature-phase-shift-keying (QPSK) modulation is an effective means of achieving high bandwidth efficiency in wired or wireless communications systems. QPSK modulation can be generated with a direct-digital-synthesizer (DDS) approach, which requires additional components, and tends to be expensive and consume power. An alternative method employs two mixers, one set to a fixed RF and the other driven by a voltage-controlled oscillator (VCO). However, mixing...  — Cecil Deisch

May 2006
When Switching Speed Is Important
Microwave frequency synthesizers provide the stable signals needed in a wide range of modern electronic systems, including communications systems, civilian and miliary radars, and electronic-warfare (EW) systems. They are available in many configuarations, from the tiny integrated circuits (ICs) embedded into cellular telephones to the rugged, rack-mount enclosures used in naval shipboard radar systems. Microwave frequency synthesizers can be compared in terms of ...  — Uri Yaniv

April 2006
Digitizer Provides Direct Sampling Of RF Signals
High-speed analog-to-digital converters (ADCs) have changed most approaches to receiver front ends. An ADC allows a good portion of the analog signal chain leading from the antenna to be eliminated. Similarly, in an instrumentation system, a high-speed ADC allows signals from a sensor to be quickly digitized with a minimum of analog processing. To demonstrate effective practices in directly digitizing RF signals, the RF subsystem for an instrumentation product used in high-energy physics...  — Uros Mavric

March 2006
Frequency Synthesizers Tune Communications Systems
Bandwidth is everything in communications. It is vital to the spread of wireless multimedia, instant data, high voice quality, and other key services. But it is also a limited resource, requiring the use of advanced amplitudeand phase-based modulation formats to squeeze the maximum amount of information into a given portion of bandwidth. One of the most critical components in enabling maximum bandwidth efficiency is the microwave frequency synthesizer. Modern synthesizers have leveraged...  — Jack Browne

March 2006
Filtering Compromises From Co-Located Systems
Co-location of different wireless-communications base stations often makes economic sense, but poses a variety of technical challenges. The approach allows carriers to still use existing infrastructure while deploying new wireless networks. The practice helps reduce capital expenditures while supporting rapid network rollouts. A decision to co-locate base stations is also impacted by the scarcity of premium base-station locations and the growing demand for aesthetically...  — André Doll , et al.

February 2006
Estimating RKE System Performance
Remote-keyless-entry (RKE) systems unlock cars from a distance by transmitting a coded radio signal over the air from a key fob to a receiverin the car. The receiver decodes the signal and controls an actuator that opens the door. An important performance benchmark of an RKE system is its useful range. This range is determined by a link-budget calculation. The most crucial factors of this calculation are the power transmitted from the key fob, receiver sensitivity, and path loss....  — Larry Burgess

November 2005
Gauging Limitations On DFD Performance
Digital frequency discriminators (DFDs) provide accurate frequencymeasurement data on pulsed and CW signals received over wide instantaneous RF bandwidths. They typically cover wide bandwidths, such as 50 to 500 MHz, 0.5 to 2 GHz, 2 to 6 GHz, 6 to 18 GHz, and 2 to 18 GHz, but are rare above 18 GHz. One of the limiting factors to achieving DFDs above 18 GHz is the problem of excess correlator phase error. What follows is a review of basic DFD capabilities and limitations, and a report on...  — William Sullivan

September 2005
Synchronized Synthesizers Aid Multichannel Systems
Direct-digital-synthesis (DDS)-based synthesizers are primarily known as agile frequency sources with low phase noise and excellent spurious performance. In many applications, they offer significant advantages over phase-locked-loop (PLL) synthesis methods like sub-hertz frequency tuning resolution, phase offset, and output amplitude control. With multiple source channels and synchronization capability now built into a pair of commercial DDS products—the four-channel AD9959 (...  — David Brandon , et al.

September 2005
Tracking Transmitter Compliance Testing
Verifying the performance of a digital communications system was once easy. When entire networks were installed and owned by a single company, and the system worked, extensive testing of the subcomponents was unnecessary. But in this age of more complex networks, with components hailing from many different sources, proper compliance testing must ensure that system-level specifications are met when all components are connected. In particular, some new approaches can help evaluate transmitter...  — Greg Le Cheminant

September 2005
Building Wireless Sensor Networks
Wireless sensor networks (WSNs) offer great promise for information capture and processing in both commercial and military applications. Successful system design and deployment includes understanding RF channel characteristics, and the choice of modulation scheme on power consumption. Such factors ultimately determine the available range and data rate of a WSN, as well as cost and battery lifetime. The increasing miniaturization of RF devices and microelectromechanical systems...  — Roshdy Hafez , et al.

June 2005
Design Improves 4.3-GHz Radio Altimeter Accuracy
Short-range radio altimeters are important safety and navigational tools in small aircraft. Usually designed as short-range frequency-modulated (FM) radars in the 4.2-to-4.4-GHz band,1 their main applications are for instrument-based approaches and landings for larger commercial aircraft, although they are also suitable for smaller aircraft and even unmanned air vehicles (UAVs). The accuracy and resolution of aviation altimeters is usually limited to a few feet due to the limited...  — Matjaz Vidmar

March 2005
Frequency Synthesizers Generate Clean Signals
Frequency synthesizers account for many of the RF and microwave signals in communications, radar, and test systems. Synthesizers come in many forms and performance levels, from tiny phase-locked-loop (PLL) integrated circuits (ICs) to rack-mountable subsystems and precision test instruments with programmable control. What follows is a brief sampling of synthesizer suppliers and their latest products. Instrument-grade frequency synthesizers offer some of the highest performance...  — Jack Browne





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