Residual FM Research Articles

Full-Distance A-RoF Transmission Experiment Utilizing Frequency-Optimized FM Conversion

Advances in the long-distance transmission of wideband A-RoF signals are critical. The world’s longest-class transmission using a practical A-RoF system is currently just over 300 km. In this system, CATV/BS/CS video signals are frequency-multiplexed with a bandwidth of 2.1 GHz and transmitted from broadcaster buildings to houses scattered throughout the country. In recent years, there is a demand to extend this bandwidth to 3.2 GHz in order to multiplex 8K/4K ultra-high-definition video. However, A-RoF transmission over 300 km in the 3.2-GHz bandwidth is difficult and no one has been achieved. Our solution is a new transmitter that improves transmission characteristics by changing the FM center frequency and suppressing harmonics. Our experiments clarified the existence of an optimum FM center frequency that is less affected by self-phase modulation, chromatic dispersion, and residual FM signal degradation. The proposed transmitter achieved the target distance and bandwidth for the first time in the world.

Greedy expansions in Banach spaces

We study convergence and rate of convergence of expansions of elements in a Banach space X into series with regard to a given dictionary \(\mathcal{D}\) . For convenience we assume that \(\mathcal{D}\) is symmetric: \(g\in\mathcal{D}\) implies \(-g\in\mathcal{D}\) . The primary goal of this paper is to study representations of an element f∈X by a series $$f\sim\sum_{j=1}^{\infty}c_{j}(f)g_{j}(f),\quad g_{j}(f)\in\mathcal{D},\ c_{j}(f)>0,\ j=1,2,\dots.$$ In building such a representation we should construct two sequences: {gj (f)} j=1∞ and {cj (f)} j=1∞ . In this paper the construction of {gj (f)} j=1∞ will be based on ideas used in greedy-type nonlinear approximation. This explains the use of the term greedy expansion. We use a norming functional \(F_{f_{m-1}}\) of a residual fm−1 obtained after m−1 steps of an expansion procedure to select the mth element \(g_{m}(f)\in \mathcal{D}\) from the dictionary. This approach has been used in previous papers on greedy approximation. The greedy expansions in Hilbert spaces are well studied. The corresponding convergence theorems and estimates for the rate of convergence are known. Much less is known about greedy expansions in Banach spaces. The first substantial result on greedy expansions in Banach spaces has been obtained recently by Ganichev and Kalton. They proved a convergence result for the Lp , 1<p<∞, spaces. In this paper we find a simple way of selecting coefficients cm (f) that provides convergence of the corresponding greedy expansions in any uniformly smooth Banach space. Moreover, we obtain estimates for the rate of convergence of such greedy expansions for \(f\in A_{1}(\mathcal{D})\) – the closure (in X) of the convex hull of \(\mathcal{D}\) .

Performance analysis of a COFDM/FM in-band digital audio broadcasting system

In this paper, we present a performance analysis of a coded orthogonal frequency division multiplexing DAB system that is power multiplexed over a commercial FM station. We model the mobile channel with a time-frequency scattering function. Results show that the performance of the FM demodulator is crucial, since the level of the residual FM signal has a strong influence on the BER performance of the COFDM system. As with other mobile communication systems, the use of interleaving greatly enhances the performances.

Highly sensitive ultrasonic flow velocity measuring method with FM component elimination

AbstractWe reported an FM ultrasonic velocimeter in which the frequency was varied by means of a ramp generator in order to reduce the number of multiple path signals. The generator requires good linearity and a necessity to change frequency with suitable speed, sometimes quite high. The authors experimentally confirm some standing wave suppressing effect using sinusoidal FM. For improvement of sensitivity, we used a second FM signal for computational processing in such a way that a new received signal with FM components eliminated was produced by adding both the received and the second FM signals. Flow velocity was thus derived from the phase between the new received and carrier signals. In elimination processing, the influence of the flow velocity and temperature change of fluid was compensated by a fixed command control system for residual FM components in a new received signal. From experiments, we were able to confirm the following: The system is effective in elimination of FM components. The measured phase shift is proportional to flow velocity and temperature change of fluid. The sensitivity for flow velocity was improved considerably. The control voltage of the fixed command control system was found usable for measurement of flow velocity, and a compensation method on the temperature change of fluid was introduced into this system.

An Experimental Study of Frequency and Power Stability of Phase-Locked Microwave Signal Sources

In setting up of microwave measurement standards of power attenuation, impedance, noise, etc. at the highest level of accuracy, high stability of frequency and power of the microwave signal source is an essential requirement. For this purpose, experimental investigations of frequency and power stabilization of microwave signals derived from klystrons and other sources under phase-locked and unlocked conditions have been carried out. The signals both locked and unlocked have been analyzed for their spectral purity, frequency drift etc. using microwave counter and spectrum analyzer. Phase-locked signals show better frequency stability, less residual FM and low noise-side bands. Source warm-up time is an important factor to achieve better frequency and power stability. Stability of the output power under locked condition improves to better than 0.1% as compared to 0.7 to 1.0% under unlocked condition. Such phase-locked microwave signal sources have been utilized for precision measurement of power, attenuatio...

Problem of speech pulling and its implementation for the design of phase-locked SSB radio systems

In the paper, the effect of speech interference on the performance of long-loop phase-locked VHF SSB radio systems is evaluated, It is shown that unless the system&apos;s reference tone is adequately protected by suitable filtering in the transmitter&apos;s audio processing, the problem of ‘speech puffing’ may occur with severe degradationin intelligibility. Furthermore, residual FM modulation of the VCO&apos;s control line (the first local oscillator) through speech interference degrades the oscillator&apos;s output spectrum with possible reduction in adjacent-channel rejection. After analysing the effect of interfering sinusoidal signals on in-lock-loop per formance, filter design criteria are established for pilot-carrier and in-band-tone SSB systems, and the theoretically predicted results are verified experimentally. Finally, alternate phase-locked receiver configurations are suggested in an attempt to overcome first-oscillator spectrum degradation in long-loop receivers.

Noise, distortion, and transmission characteristics of an M-BWO

Performance measurements have been made on an experimental FM transmitter using M-BWO. The attractive features of this oscillator are variable power control, high efficiency, wideband modulation capability and light weight. The lack of published data describing the performance of the M-BWO in terms of spectral noise distribution, spurious signals, two-tone third-order distortion, noise power ratio, instantaneous bandwidth and wide bandwidth transmission capabilities has resulted in this investigation. Performance data were obtained with an M-BWO transmitter possessing a residual FM of less than 50 KC. Spurious signals present were found to be greater than --40 db for output powers of 50 watts. Two-tone third-order distortion values varied from 1 to 2% (-37 to --40 db) and noise power ratios measured from --20 to --28 db for an rms frequency deviation of 30 MHz.

A K-Band Phase-Locked Transmitter-Receiver System for CW Balanced-Bridge Measurements

A major sensitivity limitation common to most microwave CW balanced-bridge systems must be attributed to bridge distortion noise, caused by residual FM in the transmitted signal. The described superheterodyne transceiver minimizes this limit for a narrowband K-band bridge system by utilizing precise, coherent IF detection. A phase-locked local oscillator provides means for an arbitrary, stable preselection of the in-phase or quadrature component with the help of a calibrated IF delay line. The transmitter is either 1) frequency-stabilized to a sample cavity by means of a high-gain AFC loop, or 2) phase-locked simultaneously to a K-band harmonic of a VHF quartz oscillator and to a tunable VHF oscillator (VFO). This yields flexibility in a wide range of applications, such as measuring small reflection coefficients, dielectric constants, or magnetic tensor susceptibilities (e. g., in ESR spectroscopy). Analytical expressions for phase and amplitude distortions are derived for a bridge containing one high-Q element. In the systems theory of operation, analytical formulas for the noise spectral densities and the loop errors are given, together with numerical examples. The additional receiver noise, due to residual FM and increased bridge power, is demonstrated by means of measured IF-noise spectra. A cavity-Q measurement with ±1 percent accuracy, using 5-?W incident bridge power, proves the system's capability for measurements of small reflection coefficients.