Double-sideband Amplitude Modulation Research Articles

Ultrasound-Based Directional Sound System via Double Sideband Amplitude Modulation

With unique advantages of reducing noise pollution, lengthening the propagation distance, directional sound system (DSS) is a novel technology to control sound directivity based on modulation algorithm. By using the double side band amplitude modulation (DSB-AM), we successfully design a DSS device and the experimental verification is conducted to evaluate the performance of the sound directivity with different ultrasonic array. The modulation and self-demodulation based on DSB-AM is simulated, which proves theoretically that the audible sound can be transmitted with ultrasound signal and recovered in air. The sound directivity influenced by operating frequency is simulated to determine carrier frequency. To attain optimal arrangement of the ultrasound array, the square and rectangular array is constructed in the simulation. We develop a DSS hardware configuration to investigate sound directivity of ultrasonic array. It proves that the envelope of the modulated signal is matched with the original audio signal when modulation factor m=0.5 is chosen, which can ensure the performance of transmitting sound. The sound directivity of ultrasonic array is evaluated qualitatively and quantitatively. The experiments show that the 7×7 array has the better sound directivity than the rest of arrays, where the minimum emitting angle of main beam is produced. Sound directivity demonstration solidly verifies the superiority of 7×7 array in audible music propagation.

A Single-Stage Three-Phase Bidirectional AC/DC Converter With High-Frequency Isolation and PFC

This paper presents a novel single-stage ac/dc rectifier with high-frequency isolation and bidirectional power flow capability, which is feasible to connect dc grids to ac ones. A thorough analysis is performed based on the development of an actual model as well as a fundamental one using the double-sideband amplitude modulation equations. The derived models allow the determination of the active and reactive power flow through the transformer as well as defining the operating regions for which soft commutation is achieved. Besides, the current stresses of the semiconductors devices are analyzed in detail. Experimental results obtained from a 5 kW prototype are presented and discussed in order to validate the proposed model as well as demonstrate the converter's performance and claimed advantages. The proposed concept can also be extended to dc/dc, ac/ac, and multilevel topologies.

Effects on the Performance of Parametric Loudspeaker Caused by Nonideal Ultrasound Transducer

In this paper, we report the effects on the performance of a parametric loudspeaker caused by a nonideal ultrasound transducer. The frequency contents of self-demodulated secondary wave pressure for the nonideal ultrasound transducer are first derived on the basis of Berktay's solution. Then, according to the relationship between the input signal and the envelope of primary wave pressure, the harmonic distortion and intermodulation distortion are obtained for different modulation techniques. Simulation experiments show that in the case of using the double-sideband amplitude modulation (DSB-AM) technique, the amplitudes of the fundamental frequency and intermodulation distortion components are affected by both the phase and magnitude response of the ultrasound transducer, whereas the harmonic distortion component is only affected by the phase response. In the case of using the single-sideband amplitude modulation (SSB-AM) technique, the amplitudes of the fundamental frequency component and intermodulation distortion components are only affected by the magnitude response of the transducer.

Broadband Time-Domain Measurement System for the Characterization of Nonlinear Microwave Devices With Memory

This paper describes a novel fully calibrated four channel broadband time-domain measurement system for the characterization of nonlinear microwave devices with memory. The hardware architecture of the proposed time-domain measurement system is based on a wideband sub-sampling principle. The sampling heads work at a high strobe signal repetition frequency that can be tuned between 357-536 MHz. We achieve a 40-GHz RF frequency bandwidth and a 160-MHz IF bandwidth. This instrument enables the measurement of carrier and envelope waveforms at both ports of nonlinear microwave devices driven by broadband modulated multicarriers. The test-bench is applied to the cross modulation characterization of a 15-W GaN HEMT CREE <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -band power amplifier with memory due to different biasing circuit configurations. The amplifier under test is driven by the sum of a large-signal modulated carrier (double-sideband amplitude modulation at 3.6 GHz) and a small single-tone signal at a 110-MHz offset frequency. Our significant contribution comes from the capability of the measurement system to record the time-domain waveforms of several nonadjacent modulated signals on a similar time equivalent scale for different cases of memory effects of the power amplifier under test.

Establishment of new facilities for WWVL and WWVB

A brief report of the new facilities for standard radio broadcast stations WWVL and WWVB is appropriate here for two reasons. First, the organizers of the Symposium on the Ionospheric Propagation of VLF Radio Waves, to which this issue is devoted, graciously allocated a session of the Symposium for the dedication of the new stations. characteristics and accuracy of these broadcasts arc of clear interest as a tool in VLF and LF propagfLtion r esearch. Secondly, in this first issue of the new journal, R adio Science, it is pleasant to stress an example where radio propagation activities and radio standards activities combine so nicely to fall under the broader term, radio science. dedication of the e facilities to the public ser vice was made by A. V. Astin, Director of the National Bureau of Standards. An address, The Presen t Status of National Standard s for the Basic PhysicnJ Quanti ties, by R. D. Huntoon was part of the dedication sessio n. T echnical papers descrip ti \'e of the transmitLer design , the an tenna design, the frequency and Lime con trol system, and the staLion usefulness in proyiding standard frequencies and times were presented, and are listed by Litle elsewhere in this issue. Both stations are located near Ft. Collins, Colo. Station WliVVI.1 broadcasts at 20 kc/s with a design objecti\'e of 50 kw deli\Tered to the antenna and 1.5 kw radiated. Station vYWVB broadcasts at 60 kc/s with a design objective of 50 kw delivered to the antenna and 10 kw radiated, Frequency of both is normally held to within 2 parts in lOll of the United States Frequency Standard. Deviations from the stated frequency are published for users interested in the highest possible accuracy, Frequency control is realized by a 100 mile round trip servo loop between Ft, Collins and Boulder. carrier phases as recei\red at Boulder are compared with the phase of the working atomic frequency standard. Error signals, from both the 20 kc/s and 60 kc/s transmissions, modulate a 50 lI[c/s FM telemetering transmitter at Boulder. These signals are recovered at Ft, Collins and applied to a servo-motor driven resolver at the input of each transmitter. A significant feature is that long term phase coherence of the transmissions with the atomically controlled standards at Boulder is always m.aintained, even through transmitter outages. Each antenna consists of four guyed masts 400 ft high , placed in a diamond arrangement 750 ft wide and 1880 ft long. An insulated network of aluminum. cables is suspended from each group of four masts . A down lead is suspended from the center of the cable network. present computed radiating efficiency is 2.2 percent at 20 kc/s and 24.6 percent at 60 kc/s. operating schedule is to be con tinuous on both frequencies except for reguhLr maintenfLllce periods. Station IVWVL is operated on an experimental program of b roadcasts to facilitate VLF propagation and timing resefLrch, K eyed canier station identification in International Morse Code is used . Time signals on vVvVVB co nsist of seconds pulses of 5 cycles of 1000 cycle, double-sideband amplitude modula tion . On the beginning of ettch minute (,he pulse will be in creased to one-quarter second and on the beginning of eiLch hoUl' the pulse will be thl'eequarters of tL second in dura tion. Modulation of 500 cis is used to identify the stiLtion in In tema tioIliLl Morse Code. Following the s tfttiOll call letters will be ft letter, either M or P (standing for minus or plus), and a Lhree digit number. This informa tion gi \'es the rela t ionship of the carrier frequency to atomic frequency. For instance M 130 m.eans that the carrier frequency is lower by 130 parts in 1010 than the United States Frequency Standard, This offset is incorporated to enable clocks run by the broadcas t frequency to keep time approximating Universal Time which is commonly used over the world. number is broadcast because this figure changes nearly every year and could change more often. It serves as a reminder to the user that the full fLccuracy of the transmissions can only be realized with proper corrections. 60 kc/s signal is provided as a continentftl service of the National Bureau of Standards. 20 kc/s signal is largely experimental. Both signals are now used to steer radio station WWV wi th negligible degradation of accuracy.

A Suggestion for Spectrum Conservation

Frequency stability and reduced bandwidth of single sideband suppressed carrier transmissions are important factors which assist in easing the present crowding of the high frequency bands. Present channel assignments are ordinarily predicated upon a frequency stability of 0.01 per cent and double sideband amplitude modulation. By making the transition to accurate frequency control and minimum bandwidth of transmission, many additional channels are made available. Typical examples are charted from the aeronautical mobile bands to illustrate this point. Factors affecting channel allocation are discussed.

Some Relations between Speed of Indication, Bandwidth, and Signal-to-Random-Noise Ratio in Radio Navigation and Direction Finding

Rate of phenomenon change and required speeds of indication are quite slow in many navigational and direction-finding systems, particularly those for long ranges. Therefore, the actual total required electrical bandwidths are also quite narrow, probably never greater than 100 cps or so, and in most cases much less than this. Even with complex wave forms, such small total bandwidths are possible if there can be designed a discontinuous-type bandpass filter having a multiplicity of very narrow pass bands occurring at the steady-state Fourier components of the complex signal; i.e., a comb filter. One practical method of producing such a discontinuous pass band is described briefly. In view of the interest in new modulation schemes which give an output signal-to-noise ratio which is better than the input carrier-to-noise ratio, it is pointed out that all such systems have improvement thresholds, and many navigational systems provide satisfactory information at output signal-to-noise ratios lower than these threshold values. When this is the case, single-sideband and doublesideband amplitude modulation produce the most sensitive systems. When postdetection bandwidth is very much narrower than predetection bandwidth, many navigational systems will perform satisfactorily even though the carrier-to-noise ratio at the input to the final detector is appreciably less than unity. When this is so, the phenomenon of apparent demodulation is encountered.