Transmitter Operation Research Articles

A 24-channel WDM transmitter for access systems using a loop-back spectrally sliced light-emitting diode

A 24-channel wavelength-division-multiplexed (WDM) transmitter for local access networks has been demonstrated by applying a novel loop-back spectral slicing, optical timing delay, and multiplexing method to a light-emitting diode. Set-and-forget transmitter operation with self-aligned channel wavelengths was realized. Error-free transmission over 16 km of fiber at 50 Mb/s per channel using the WDM transmitter was demonstrated.

True time-delay fiber-optic control of an ultrawideband array transmitter/receiver with multibeam capability

A true time-delay beamformer based on a fiber-optic dispersive prism is developed and characterized. The beamformer is used to control an ultrawideband time-steered array antenna, which is a significant improvement over inherently narrowband phased-array antennas. The time-steered transmitter antenna consists of eight broadband spiral elements in a sparsely-populated array. In transmit mode the bandwidth is microwave-component limited to 2-18 GHz. The transmitter shows an unprecedented performance with >100/spl deg/ azimuth steering and no observed squint over the full frequency range. We also extend the beamformer functionality and demonstrate, we believe for the first time, fully-independent dual-beam dual-frequency ultrawideband antenna transmitter operation. Furthermore, the beamformer is shown to be capable of controlling the transmitter under pulsed operation with microwave pulse-widths as short as 75 ps. In the phase-steered receive mode, the antenna is component-limited to two elements and a frequency range of 6-16 GHz. However, we can still demonstrate squint-free receiver steering over >70/spl deg/ azimuth over the full available frequency range. >

Temperature measurements of a high-power microwave feedhorn window

Temperature measurements of a high-power microwave feedhorn window during transmitter operation at 365 kW CW and 8.5 GHz made using an imaging infrared radiometer are discussed. The window under investigation was constructed of HTP-6, a high-thermal-performance material developed to shield the Shuttle Orbiter from the heat of reentry. The measurement technique is described and experimental results are presented. The window performed adequately at 365 kW CW with a center temperature of 475 degrees C. The tests verify that HTP-6 can be used as a window material or a support structure in high-power waveguide at power densities of 1.47 kW/cm/sup 2/ for extended periods of time, with no change in its mechanical characteristics. >

Characterization of an optoelectronic terahertz beam system

The performance of an optoelectronic terahertz (THz) beam system is described. The transmitter operation is based on the repetitive, subpicosecond laser excitation of a Hertzian dipole antenna embedded in a charged coplanar line. With this transmitter electromagnetic beams of 1/2 cycle THz pulses at a repetition rate of 100 MHz are produced. The associated optoelectronic receiver is gated in synchronism with the excitation of the transmitter by subpicosecond pulses from the same laser source. With this receiver, the 10-nW beams of THz pulses were observed with a signal-to-noise ratio greater than 10000:1. Several sources contributing to the noise of the receiver are discussed, together with ways to reduce them. With an integration time of 125 ms, a signal-to-noise ratio of 1 is obtained for a THz beam with an average power of 10/sup -16/ W. The receiver operates in the sampling mode and has a time resolution of 0.5 ps. >

Outer zone electron precipitation produced by a VLF transmitter

By means of high‐resolution pitch angle measurements made by a magnetic‐focusing electron spectrometer on the S3‐3 satellite while in the drift loss cone region of the magnetosphere, characteristics of fluxes of 108‐ to 654‐keV electrons precipitated in the inner zone, in the slot region, and in the outer zone of the magnetosphere are all shown to be consistent with the precipitation's having been produced by the same ground‐based VLF transmitter, UMS. Pitch angle measurements are used to locate the longitude of precipitation. The temporal pattern of transmitter operation obtained from synoptic data from a ground‐based VLF receiver is used along with drift rate calculations to predict the electron energies as a function of L shell which should be observable by the S3‐3 instrument. The predicted energy response is then compared with the in situ observations, getting complete agreement. Finally, wave‐particle resonance calculations are made for each of the three regions. The study indicates that ground‐based VLF transmitters, which have previously been shown to produce precipitation in the inner zone and slot regions, are almost certainly instrumental in precipitating electrons in the outer zone also.

The dynamic modelling of differential pressure transmitters

The paper describes the dynamic modelling of two force-balance differential-pressure transmitters, one pneumatic and one electronic. In both cases an experimental transmitter transfer function is found from frequency response tests. This is then compared with a theoretical transfer function calculated from the differential equations describing the principles of transmitter operation. The theoretical transfer function for the pneumatic transmitter is fourth order; there is reasonable agreement between theoretical and experimental transfer-function coefficients. A more detailed model of the adjustable fluid damping mechanism is necessary for closer agreement to be obtained. The theoretical transfer function describing the electronic transmitter is third order, with close agreement between experimental and theoretical transfer-function coefficients. The bandwidth of the electronic differential-pressure transmitter tested was between 0 and 0.3 Hz compared with a bandwidth of between 0 and 3 Hz for the pneumatic transmitter. This large difference is mainly attributable to the electronic transmitter having a larger damping constant and a demodulator low-pass filter with a long time constant.

The modulated precipitation of radiation belt electrons by controlled signals from VLF transmitters

The first direct observations of the precipitation of radiation belt electrons by the controlled injection of VLF signals from a ground based transmitter were recently reported from data acquired in the SEEP (Stimulated Emission of Energetic Particles) experiment. That outstanding example of time‐correlated wave and electron data has now been enhanced by the finding of four additional modulated events out of 65 satellite passes when one of the U. S. Navy VLF transmitters at Cutler, Maine (NAA) or at Annapolis, Maryland (NSS) was being modulated in a 3s ON/2s OFF format. During each of these events the fluxes of precipitating electrons were observed repeatedly to display a characteristic time behavior with respect to the transmitter modulation: a relatively slow rate of increase after start of the ON period leading to a maximum about 2 seconds later. Details of this consistent pattern and the statistics of occurrence of modulation events are presented along with comparisons of the absolute fluxes of precipitating electrons observed during normal transmitter operation with those recorded when one of the transmitters was modulated.

Design for system reliability in personal radio signaling

Innovative techniques and attention to frequently-ignored factors have been combined in a new personal radio signaling system. Accessed by means of Touch-Tone®service, customer dialing errors are effectively controlled through the use of self-checking numbers, eliminating a common cause of missed or false signals. A multiplicity of radio transmitters are arranged to provide adequate building penetration for the entire service area. Simultaneous transmitter operation and low speed, digital receivers work together to make use of multipath radio propagation. Redundancy of equipment and terminal functions assure that electronic failures result in minimal impairment of service. Combining all of the above design features has resulted in a service that is significantly more reliable than that which is provided by systems of earlier design.

Unobscured Aperture Stigmatic Telescopes

A large aperture diffraction limited off-axis optical system adaptable to duplexed transmitter and receiver operation has been designed. The system employs tilted stigmatic telescopes consisting of paraboloidal primary and secondary mirrors. The magnifications and tilts are selected to remove focal plane tilt.

Radio scintillation on stellar signals during artificial ionospheric modification

Scintillation signals from the radio sources Cyg A and Cass A were taken at 26 MHz on nine evenings in 1971 and 1972 at times of ionospheric modification by a high-powered hf transmitter near Boulder, Colorado. The scintillation character often changes significantly during modification. The artificially produced scintillations are either rapid and random or deep long-period modulation. The random scintillations and ionogram signatures (spread F and wide- band attenuation) are directly correlated with transmitter operation and are interpreted in terms of small irregularities (dimensions of 1 to 4 km), whereas the long-period modulation can be interpreted in terms of large irregularities (dimensions of about 10 to 100 km). Small irregularities are similar to natural ones and require a short time to develop, less than a few seconds, but the large irregularities differ from the natural ones and usually take from 5 to 15 min after transmitter on'' to develop. (auth)