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Pressure of a button on a crystal-controlled transmitter causes generation of a tone. The tone modulates the FM transmitter which in turn radiates by way of the enclosed loop antenna, through the radio-frequency-transparent wall of the transmitters case to the receiver.
An automatic frequency control circuit for an FM television transmitter is described. The frequency of the transmitter is sampled during what is termed the back porch portion of the horizontal synchronizing pulse which occurs during the retrace interval, the frequency sample compared with the frequency of a reference oscillator, and a correction applied to the frequency of the transmitter during this portion of the retrace interval.
Results of an experimental study of the effect of discharges in oxygen on the oxide thickness and transmittance of aluminum filters. The studies were performed by exposing the filters to RF discharges and dc glow discharges in oxygen. In all experiments except one in which an aluminum ring was used as the cathode an increase in the transmittance of the filters is noted. It is thus demonstrated that the transmittance of aluminum filters increases on exposure to electrical discharges in oxygen, although it is not certain whether this phenomenon is caused by atomic oxygen.
The paper examines the feasibility of a technique to simulate ULF waves in the ionosphere using controlled particle precipitation. In the proposed model of micropulsation generation, a pulse from a VLF ground transmitter (or satellite transmitter) is injected into the magnetosphere and follows the earth's static magnetic field lines to a region near the magnetic equatorial plane where it begins to interact strongly with energetic electrons through gyroresonance. VLF emissions are produced in the gyroresonance interaction, and numerous energetic electrons are scattered into the loss cone, proceeding down the magnetic field lines and precipitating into the lower ionosphere where they create large-scale enhancements of ionization. The results lend support to the idea of attempting to produce detectable ULF waves by using ground- or satellite-based VLF transmitters.
The design, build, and test of an engineering breadboard Ku band quadraphase shift keyed and wideband frequency modulated transmitter are described. This orbiter Ku band transmitter drawer is to simulate the orbiter transmitter and meet the functional requirements of the orbiter communication link.
The design, fabrication tests, and engineering model components of a 10.6 mum wideband transceiver system are reported. The effort emphasized the transmitter subsystem, including the development of the laser, the modulator driver, and included productization of both the transmitter and local oscillator lasers. The transmitter subsystem is functionally compatible with the receiver engineering model terminal, and has undergone high data rate communication system testing against that terminal.
A diagnostic technique to obtain the cold-plasma density profile in the magnetosphere is introduced. This method uses satellite measurements of group delay and pulse duration of VLF signals from ground transmitters in conjunction with a detailed ray-tracing analysis. An iterative method is involved which starts with an approximate density profile, computes the ray paths for that profile, and then compares the properties of the rays that reach the satellite location with the actual satellite measurements. The density profile is then modified to account for any discrepancies between the two results. The same process is repeated with the new profile until one has reasonable agreement between the data and ray-tracing results. This method is applied to the case of an Imp 6 pass, where strong signals from the Siple VLF transmitter were observed for over 25 min. Good agreement is found between the results of the proposed technique and the well-known ground whistler techniques of cold-plasma diagnostics. The results also serve to illustrate the wide diversity of propagation paths from ground transmitters to high-altitude satellites during VLF wave-injection experiments.
Results are reported for an experiment in which VLF waves from a transmitter in Antarctica were injected into the magnetosphere along geomagnetic field lines and detected near the magnetic equatorial plane by high-altitude spacecraft. The purpose of this experiment was to conduct a controlled in situ study of VLF wave-particle interactions and to determine the propagation characteristics of the injected waves in the magnetosphere, the regions where VLF emissions are produced, and the effective volume of the magnetosphere illuminated by the transmitter. The results indicate that: (1) the bulk of the satellite receptions occurred during periods of quieting following magnetic disturbances, (2) receptions generally occurred inside the plasmapause, (3) the spacecraft detected predominantly unducted waves, (4) the injected signals could illuminate a large volume of the magnetosphere, and (5) VLF emissions were triggered by nonducted transmitter pulses.
An infrared heterodyne radiometer (IHR) was used to measure atmospheric transmittance at selected hydrogen fluoride (2.7 micrometer) and deuterium fluoride (3.8 micrometer) laser transitions. The IHR was installed aboard a KC-135 aircraft for an airborne atmospheric measurements program that used the sun as a backlighting source for the transmission measurements. The critical components are: a wideband indium antimonide (1nSb) photomixer, a CW HF/DF laser L0, a radiometric processor, and a 1900 K blackbody reference source. The measured heterodyne receiver sensitivity (NEP) is 1.3 x 10 to the -19th power W/Hz, which yields a calculated IHR temperature resolution accuracy of delta I sub S/-3 sub S = 0.005 for a source temperature of 1000 K and a total transmittance of 0.5. Measured atmospheric transmittance at several wavelengths and aircraft altitudes from 9.14 km (30,000 ft) to 13.72 km (45,000 ft) were obtained during the measurements program and have been compared with values predicted by the AFGL Atmospheric Line Parameter Compilation.
A method for aligning the transmitter and receiver telescopes of a lidar is proposed which involves the use of a small high-quality corner tube reflector placed immediately in front of the transmitter in such a way that a small fraction of the transmitted radiation is reflected to the receiver. The reflected radiation is brought to a focus in a focal plane where it appears as a small red dot and is superimposed on the image of the distant scene. The dot and the target appear in the same plane and may be brought to coincidence by moving the transmitter-receiver pair together until the image of the target falls on the red dot. The alignment is concluded by imaging the red dot onto an IR detector.
New observations in the magnetosphere of coherent VLF waves from the Siple Station, Antarctica, transmitter and associated VLF emissions triggered by the transmitter signals are reported. The data analyzed were acquired on the EXOS-B high-altitude satellite during the period July 15-September 7, 1979, during joint VLF wave-injection experiments involving scientists from Kyoto, Tokyo, and Stanford universities. The experiments were carried out to gain a deeper understanding of the interactions between coherent VLF waves and energetic particles in the magnetosphere, in particular, the whistler-mode instability through which both natural and stimulated VLF emissions are produced. Analysis of the emission-triggering events provides strong evidence that the triggering took place inside whistler-mode ducts and that the emissions reached the satellite only after being scattered at one end of the ducts by ionospheric irregularities. It is concluded that in the noon sector of the magnetosphere, the amplitude of nonducted signals from the Siple transmitter is generally less than the threshold level necessary for triggering in the nonducted mode.
The SEASAT-A synthetic aperture radar, the first spaceborne SAR, utilized an all solid state RF signal synthesizer and L-band transmitter to drive a corporately fed flat plate array. The RF signal synthesizer generated a linear FM ""CHIRP'' waveform and provided stable CW reference signals used to upconvert the received signal to a unified S-band downlink channel, and to synchronize satellite control logic. The transmitter generated 1200 watts peak RF power (66 watts average) at a center frequency of 1.275 GHz from 354 watts of DC prime power. Linear FM CHIRP swept symmetrically around the center frequency with a bandwidth of 19.05 MHz and a pulse duration of 33.8 sec. Pulse repetition rate was variable from 1647 to 1944 pps. These transmitter signal parameters combined with the flat plate 34 x 7.5 ft aperture at an orbital altitude of 498 miles and a look angle 20 deg off nadir gave the SAR an 85 foot resolution over a 15.5 mile wide swath.
The relative probability of detecting randomly distributed CW transmitters as a function of the fraction of the sky which is searched (in a fixed time interval) is given. It is shown that the probability of detecting such a class of transmitters with a given receiving system is a maximum if the entire sky is searched, provided that the receiving system is sufficiently sensitive to detect the nearest transmitter in the allocated time and that the integration time - bandwidth product in a specified direction is greater than 8.
The engineering development of a solid-state transmitter amplifier operating in the 20-GHz frequency range is described. This effort involved a multitude of disciplines including IMPATT device development, circulator design, multiple-diode circuit design, and amplifier integration and test. The objective was to develop a transmitter amplifier demonstrating the feasibility of providing an efficient, reliable, lightweight solid-state transmitter to be flown on a 30 to 20 GHz communication demonstration satellite. The work was done under contract from NASA/Lewis Research Center for a period of three years. The result was the development of a GaAs IMPACT diode amplifier capable of an 11-W CW output power and a 2-dB bandwidth of 300 MHz. GaAs IMPATT diodes incorporating diamond heatsink and double-Read doping profile capable of 5.3-W CW oscillator output power and 15.5% efficiency were developed. Up to 19% efficiency was also observed for an output power level of 4.4 W. High performance circulators with a 0.2 dB inserting loss and bandwidth of 5 GHz have also been developed. These represent a significant advance in both device and power combiner circuit technologies in K-band frequencies.
A proposed conceptual design to increase the output power of an existing X-band radar transmitter used for planetary radar exploration from 365 kW to 1 MW CW is presented. The basic transmitter system requirements as dictated by the specifications for the radar are covered. The characteristics and expected performance of the high-power klystrons are considered, and the transmitter power amplifier system is described. Also included is the design of all of the associated high-power microwave components, the feed system, and the phase-stable exciter. The expected performance of the beam supply, heat exchanger, and monitor and control devices is also presented. Finally, an assessment of the state-of-the-art technology needed to meet system requirements is given and possible areas of difficulty are summarized.
The combined operation of a high or medium frequency ground transmitter and a VLF transmitter for enhanced ionospheric heating is examined. The high or medium frequency transmitter operating in a pulsed mode produce short-scale density striations that can render the nonlinear mode conversion of the subsequently launched VLF waves into lower hybrid waves. Also if the VLF waves are intense enough, they can excite meter-scale density striations and lower hybrid waves via parametric instabilities. The expected ionospheric effects of the system are discussed.
Bidirectional optical properties of leaves must be adequately characterized to develop comprehensive and reliably predictive canopy radiative-transfer models. Directional reflectance and transmittance factors of individual corn and soybean leaves were measured at source incidence angles (SIAs) 20, 45, and 70 deg and numerous view angles in the visible and NIR. Bidirectional reflectance distributions changed with increasing SIA, with forward scattering most pronounced at 70 deg. Directional-hemispherical reflectance generally increased and transmittance decreased with increased SIA. Directional-hemispherical reflectance factors were higher and transmittances were lower than the nadir-viewed reflectance component.
The principal considerations in the design of fiber-optic transmitters for highly phase-stable radio frequency and microwave analog transmission are discussed. Criteria for a fiber-optic transmitter design with improved amplitude and phase-noise performance are developed through consideration of factors affecting the phase noise, including low-frequency laser-bias supply noise, the magnitude and proximity of external reflections into the laser, and temperature excursions of the laser-transmitter package.