7,199 research outputs found
Design of a 12 channel fm microwave receiver
The design, fabrication, and performance of elements of a low cost FM microwave satellite ground station receiver is described. It is capable of accepting 12 contiguous color television equivalent bandwidth channels in the 11.72 to 12.2 GHz band. Each channel is 40 MHz wide and incorporates a 4 MHz guard band. The modulation format is wideband FM and the channels are frequency division multiplexed. Twelve independent CATV compatible baseband outputs are provided. The overall system specifications are first discussed, then consideration is given to the receiver subsystems and the signal branching network
Program on application of communications satellites to educational development: Design of a 12 channel FM microwave receiver
The design, fabrication, and performance of elements of a low cost FM microwave satellite ground station receiver is described. It is capable of accepting 12 contiguous color television equivalent bandwidth channels in the 11.72 to 12.2 GHz band. Each channel is 40 MHz wide and incorporates a 4 MHz guard band. The modulation format is wideband FM and the channels are frequency division multiplexed. Twelve independent CATV compatible baseband outputs are provided. The overall system specifications are first discussed, then consideration is given to the receiver subsystems and the signal branching network
Core-Accretion Model Predicts Few Jovian-Mass Planets Orbiting Red Dwarfs
The favored theoretical explanation for giant planet formation -- in both our
solar system and others -- is the core accretion model (although it still has
some serious difficulties). In this scenario, planetesimals accumulate to build
up planetary cores, which then accrete nebular gas. With current opacity
estimates for protoplanetary envelopes, this model predicts the formation of
Jupiter-mass planets in 2--3 Myr at 5 AU around solar-mass stars, provided that
the surface density of solids is enhanced over that of the minimum-mass solar
nebula (by a factor of a few). Working within the core-accretion paradigm, this
paper presents theoretical calculations which show that the formation of
Jupiter-mass planets orbiting M dwarf stars is seriously inhibited at all
radial locations (in sharp contrast to solar-type stars). Planet detection
programs sensitive to companions of M dwarfs will test this prediction in the
near future.Comment: 10 pages including 2 figures; accepted to ApJ Letter
Speech May be Free, and Talk Cheap, but Judges Can Pay a Heavy Price for Unguarded Expression
Constraints on the Intergalactic Transport of Cosmic Rays
Motivated by recent experimental proposals to search for extragalactic cosmic
rays (including anti-matter from distant galaxies), we study particle
propagation through the intergalactic medium (IGM). We first use estimates of
the magnetic field strength between galaxies to constrain the mean free path
for diffusion of particles through the IGM. We then develop a simple analytic
model to describe the diffusion of cosmic rays. Given the current age of
galaxies, our results indicate that, in reasonable models, a completely
negligible number of particles can enter our Galaxy from distances greater than
Mpc for relatively low energies ( GeV/n). We also find
that particle destruction in galaxies along the diffusion path produces an
exponential suppression of the possible flux of extragalactic cosmic rays.
Finally, we use gamma ray constraints to argue that the distance to any
hypothetical domains of anti-matter must be roughly comparable to the horizon
scale.Comment: 24 pages, AAS LaTex, 1 figure, accepted to Ap
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