Refuge dspersion was manipulated for a hybrid stone crab population (Menippe rnercenaria X M, adina) in the northeastern Gulf of Mexico. Den quality and quantity were controlled with prefabricated concrete modules (77 X 58 X 30 cm), each representing a resource (i.e. refuge) patch. Inter-patch distances differed among 3 treatments: a widely spaced, uniform patch pattern ('Wide'), an intermediate or mixed patch pattern ('Mixed'), and a closely spaced, uniform patch pattern ('Close'). Wide modules harbored significantly more crabs and larger crabs than &d Mixed or Close modules. Sex ratios &d not differ among treatments, but Wide modules harbored proportionately more mated pairs. Tagged crabs were not long-term residents of a single den, but crab resightings differed among treatments and were greater for females than males. We suggest that prey depletion on soft bottom is a function of refuge dispersion, and that the resulting resource mosaic determines local abundance of stone crabs, residency patterns by size and sex, and male mating success.
Development ofdigital satellite L-band tuners is taking place under pressure to reduce costs. Direct conversion is attractive, as it reduces component count. There is no SAW filter and the absence of an image means the front-end tracking filter is greatly simplified. This IC shows feasibility of direct conversion for DBS, testing solutions to the issues: wide dynamic range, VCO-RF interactions and broadband quadrature accuracy.A tuner sees multiple channels at similar power levels in the range 950MHz to 2150MHz after first down-conversionby theLNB. Thus good 2nd-and 3rd-order linearity is needed to avoid intermodulation products that may mixin-band. Higher linearity eases the requirements on the tracking filter. Typically, an input IP3 of at least +4dBm is required, but in the absence of a tracking filter, it is estimated that this would have to rise to +10dBm.Signal power may vary by 240dB due to external factors, so gain control is needed. As the mixers are likely to make a significant contribution to distortion, some controlled attenuation at RF is desirable. The target noise figure is 12dB and IQ quadrature error across the full RF and baseband frequency ranges must be no more than 3".Adirect conversion architecture with on-frequency VCO is likely to haveproblemswithRF-VCOinteractions.Any1eakage ofRFto the VCO tankwill cause spurs leadingto anincreaseinintegratedphase jitter in the LO. Consideration ofmaintainingamplifiernoise figure, VCO phasenoise andmaximumRFinputlevels shows thatRF-VCO isolation better than lOOdB is required.The architecture is showninFigure 1. There are 2 keypoints: 1) The oscillator is run at half frequency and doubled on-chip, so any RF leakingto theVCO is welloutside the tank resonance. 2) Digitalgain control allows optimumgaindistribution to meet noise andlinearity requirements under all signal conditions. A passive switched attenuator in front of the pre-amp protects the pre-amp and mixers from high signal levels, while maintaining the correct input impedance and sufficient bandwidth. This scheme also meets therequirement for noise figure degradation with gain reduction of no more than 1dB per dB.The differential input passes through a switched attenuator to a fixed-gain pre-amp. This drives doubly-balanced mixers followed by the first (variable gain) I and Q baseband amplifiers, each ofwhich has an open collector output to current-drive a simple external supply-referenced filter. The second baseband stage gain is variable from 29.25 to 35dB and dcfeedbackminimizes offsets. The feedback amplifier has an open-collector output to an external supply-referenced resistor. The final (single-ended) output is referenced to 2.5V.To double the VCO output across more than an octave of frequency, the VCO output is buffered and fed through a 2nd-order polyphase network to generate approximate phase quadrature signals (Figure 2). Any remaining IQ phase error is trimmed-out by a delay-locked loop (DLL). The phase detector in this loop consists of a mixer followed by an integrator. Mixing I and Q f...
Effects in a Public Address System. R. D. FAY, Massachusetts Institute of Technology. (15 minutes).--In studying the effects produced by two or more sources simultaneously emitting the same sounds, it has frequently been noticed that all of the sound appears to come from the nearest source provided the difference in distances between the observer and the sources lies between fairlv definite limits.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.