International intercomparison of horn gain at X-band

An international intercomparison of horn gain and polarization measurements at X-band has previously been completed. There were seven participating laboratories with the National Institute of Standards and Technology serving as the pilot laboratory. Two X-band pyramidal standard gain horns with a nominal gain of 22 dB served as the traveling standards. Quantities measured included on-axis fixed frequency gain at 8, 10, and 12 GHz, swept frequency gain between 8-12 GHz and polarization characteristics at the three fixed frequencies. All laboratories performed the fixed frequency-gain measurements. The swept-frequency and polarization measurements were optional, with four laboratories performing swept-frequency measurements and three laboratories measuring polarization. The results of the gain measurements generally agreed within the reported uncertainties which were of the order of 0.1 dB or less     

A Mixed-Signal Approach Towards Linear and Efficient N-Way Doherty Amplifiers

A mixed-signal approach for the design and testing of high-performance N-way Doherty amplifiers is introduced. In support of this, an analysis of N-way power-combining networks is presented-in particular, their optimum design-by examining the relationship between the drive conditions of the active devices and input power. This analysis makes no prior assumption on the network topology and facilitates free-to-choose levels for the high-efficiency power back-off points. By comparing the results of this analysis with prior work, it is shown that very specific drive conditions apply to traditional three-way Doherty amplifier implementations to obtain simultaneously high-efficiency and high-linearity operation. To support these conclusions, a 15-W three-way Doherty amplifier was constructed using Philips GEN4 LDMOS devices featuring three separate inputs to independently drive the main and peaking devices. By testing this three-way amplifier with a custom-built measurement setup, capable of providing multiple digitally controlled coherent RF input signals with high spectral purity, a unique flexible amplifier concept is created resulting in a record-high efficiency for LDMOS-based Doherty amplifiers over a 12-dB back-off power range     

International comparison of power measurements at 33 GHz(GT-RF/92-4)

A measurement comparison of effective efficiency has been carried out between eight national metrology laboratories at 33 GHz in rectangular waveguide IEC R320. Two waveguide thermistor mounts were measured. The following national laboratories participated: BNM-LCIE (France), NIST (U.S.), NRC (Canada), KRISS (Korea), CSIRO (Australia), PTB (Germany), NMi VSL (The Netherlands), and NPL (U.K.). The Bureau National de Metrologie-Laboratoire Central des Industries Electriques (France) acted as the pilot laboratory for the comparison. Excellent harmony is observed between results given by the participants, especially for the item LCIE-92021     

CCE intercomparison of AC-DC transfer standards

A worldwide comparison is described covering both AC voltage and AC current measurements in the frequency range from 40 Hz to 1 MHz. Results are consistent within 10-20 p.p.m. at low voltage and frequency, but differ by up to 100 ppm at high voltage and frequency. For currents of tens of milliamperes the results are consistent within 40 ppm     

On the design of unilateral dual-loop feedback low-noise amplifiers with simultaneous noise, impedance, and IIP3 match

This work describes the theory and design of a nonenergetic dual-loop feedback low-noise amplifier (LNA) that provides maximum unilateral gain and simultaneous noise and impedance matching conditions. The dual-loop feedback is implemented in the form of transformer current-feedback and inductive series feedback (emitter degeneration). The current-feedback transformer is also used to neutralize the base-collector capacitance (C/sub bc/), by combining it with a properly dimensioned shunt admittance at the collector output. The result is a single-transistor unilateral-gain amplifier with high isolation and good stability, eliminating the need for a cascode stage and thus enableing the use of a lower dc-supply voltage. For the complete LNA, simple design equations are derived for the unilateralization, noise, and impedance matching requirements. Finally, second-harmonic tuning at the source improves the linearity without compromising the simultaneous noise and impedance match. To verify the presented theory, a 900-MHz hybrid Si BJT LNA has been implemented, which achieves 1.3-dB noise figure, 15-dB gain, -55dB isolation, and +10dBm IIP3 using a conventional double poly transistor, consuming I/sub C/=2.5 mA at V/sub CE/=1.5 V.     

Meetings of the Future: Enhancing Group Collaboration with Group Support Systems

Meetings frequently fail to meet the objectives or expectations of the participants. The factors that diminish performance, including creativity, can be addressed through the application of electronic group support systems. A brief history of group support systems is provided. Recent developments are examined, and it is suggested that the systems offer more than the earlier planning function. Specifically they permit more opportunities for designing meeting processes to meet the contingent requirements of each group of users. As such the systems do not remove the need for leadership, merely provide ways through which leadership efforts can be supported and enhanced.     

Predicting the Structure and Dynamics of Membrane Protein GerAB from Bacillus subtilis

Bacillus subtilis forms dormant spores upon nutrient depletion. Germinant receptors (GRs) in spore’s inner membrane respond to ligands such as L-alanine, and trigger spore germination. In B. subtilis spores, GerA is the major GR, and has three subunits, GerAA, GerAB, and GerAC. L-Alanine activation of GerA requires all three subunits, but which binds L-alanine is unknown. To date, how GRs trigger germination is unknown, in particular due to lack of detailed structural information about B subunits. Using homology modelling with molecular dynamics (MD) simulations, we present structural predictions for the integral membrane protein GerAB. These predictions indicate that GerAB is an α-helical transmembrane protein containing a water channel. The MD simulations with free L-alanine show that alanine binds transiently to specific sites on GerAB. These results provide a starting point for unraveling the mechanism of L-alanine mediated signaling by GerAB, which may facilitate early events in spore germination.     

Field experiences with collaboration technology: A comparative study in Tanzania and South Africa

In the field of development, Information & Communication Technology (ICT) is often hailed and cursed at the same time. ICT offers great promise to enhance development activities' efficiency and effectiveness yet the literature is littered with examples of failure. A particular challenge concerns the application of ICT to support collaboration in development contexts. In this paper, we report on field experiences with one particular type of collaboration technology, Group Support Systems (GSS), and its role in supporting groups engaged in development activities. Being an North-American invention, research into GSS is predominantly focused on Western Euro-American settings. GSS field studies in other cultural environments are scarce. The objective of our study is to explore and compare the applicability of GSS in two particular environments: Tanzania and South Africa. Our data suggest that the use of GSS is evaluated positively in both countries, although Tanzanian groups perceived more benefits. In South Africa, top management displayed very open and non-conservative behavior towards the technology, while in Tanzania hesitance from top management can be expected to be the greatest hindrance for GSS acceptance and application. The data further indicate that GSS do not replace existing meeting customs, but rather introduce new ones that co-exist next to the traditional ones. A key difference between application of GSS in western and African environments is a stronger focus on the electronic part of discussions in Africa. Anonymity is perceived as the key feature.