中频PCM／FM信号全软化FM解调的一种实现方法

遥测传输技术是通信领域的一个分支，正在向高码速率、多功能方向发展，可将软件无线电的概念运用到遥测领域中，采用软件无线电的思想实现接收机的软件化，完成多模式信号的解调。为了降低系统的复杂度和提高系统的精度，要求将数字化的时刻尽量提前。受到器件水平的限制，还无法做到直接射频采样，而只能对中频信号进行采样，并将采样信号存储之后再对其进行处理。文中针对中频数字化后的PCM／FM信号的全软化FM解调展开研究。     

FM信号单音干扰效果评估方法

FM信号受单音干扰时,有时无法获取干扰信号信息,但易获取输入信号和输出信号信息。提出将均方误差公式进行改进,并与干信比这一指标相关联,间接对FM信号进行单音干扰效果评估的方法。首先,建立了FM信号仿真模型,分析了不同信噪比下FM解调信号的波形失真情况;其次,分析了FM调制信号受到单音干扰时,在不同干信比下FM解调信号的波形失真情况;然后,用均方误差公式来表示模拟信号失真度,分析其与干信比的变化曲线,并对均方误差公式进行改进,仿真研究后得到新的评估指标;最后,分析了新评估指标与干信比和占空比的关系。     

PCM/FM遥测信号软件解调算法研究

针对目前航天测控中PCM/FM遥测系统使用的调频非相干解调技术存在解调门限较高的问题,研究一种基于最大似然思想的多符号检测(Multi-Symbol Detection, MSD)解调方法。介绍多符号检测原理,并针对以往同步方法的不足,研究一种将码元判决过程与同步相结合的变步长同步方法。仿真和测试结果表明,基于MSD解调PCM/FM信号是一种非常有效的方法。对下一代遥测信号解调系统的研制具有重要的应用价值。     

TDLAS中激光器IM/FM相位延迟实时测量方法研究

在基于谐波检测法的TDLAS（可调谐二极管激光吸收光谱)系统中,在通过改变激光器注入电流实现激光频率扫描和调制的同时引起激光强度的变化,激光器输出信号的强度-频率(IM/FM)相位延迟_m的变化将直接导致谐波系数波动,带来系统误差。提出一种利用光纤迈克尔逊干涉仪实现激光器输出信号强度-频率(IM/FM)相位延迟_m的测量方法,能在激光器调制测量的同时实时测量相位延迟_m。实验结果表明,激光器输出信号强度-频率(IM/FM)相位延迟_m与理论值π有一定差异。研究提出的方法可以用来实时补偿信号强度-频率(IM/FM)相位延迟_m对气体浓度测量结果的影响。     

ASYMMETRIC DISTRIBUTION OF SAW POWER FLUX EMITTED FROM LINEAR FM IDT

According to theoretical prediction,the distribution of acoustic wave power flux launched inboth directions by the linear FM interdigital transducer(IDT)is a symmetrical in nature.Methodsof acousto-optic diffraction have been employed to detect acoustic field distrbution of linear FM IDT.Three unapodized linear FM IDT which have different parameters are examined.These transducersare formed with aluminum electrodes deposited on the piezoelectric substrates of Y-cut Z-pro-pagating lithium niobate.Expermental results show that surface acoustic wave(SAW)power fluxradiated from the high frequency portion of linear FM interdigital transducer is stronger than thatfrom the low frequency one.The asymmetry increases with the number of the effective fingerpairs.In general,the asymmetry increases with the exciting frequency but the relation betweenthem is not monotonic.Based on the equivalent circuit,numerical evaluations of the asymmetricdistribution have been made.The theoretical curves essentially agree with the     

直接中频采样PCM／FM数字接收机的设计与实现

近年来，随着软件无线电技术，数字信号处理技术以及大规模可编程器件、高速ADC芯片的长足发展和进步，数字接收机设计已成为接收机技术的发展方向。理想软件无线电技术要求对射频信号进行直接采样，而将尽可能多的通信功能用软件加以实现，但目前的技术要实现这一目标还存在不小的困难，一种比较切实的方案是对中频信号进行采样，而将信号的解调、解扩、均衡、判决等处理任务用DSP或FPGA加以实现，从而构成直接中频采样的数字接收机。     

The pH Probe CypHer™5E is Effectively Quenched by FM Dyes

Concurrent imaging of spectrally distinct fluorescence probes has become an important method for live-cell microscopy experiments in many biological disciplines. The technique enables the identification of a multitude of causal relationships. However, interactions between fluorescent dyes beyond an obvious overlap of their fluorescent spectra are often neglected. Here we present the effects of the well-established fluorescent dyes FM®2-10 or FM®1-43 on the recently introduced pH-dependent probe CypHer?5E. Spectrophotometry as well as live-cell fluorescence microscopy revealed that both FM dyes are effective quenchers of CypHer?5E. Control experiments indicated that this effect is reversible and not due to bleaching. We conclude that, in general, parallel measurements of both dyes are possible, with low FM dye concentrations. Nevertheless, our results implicate that special care has to be taken in such dual colour experiments especially when analysing dynamic CypHer?5E signals in live-cell microscopy.     

Selective adaptation to linear frequency-modulated sweeps: evidence for direction-specific FM channels?

Psychometric functions were obtained for detection of linear frequency-modulated pure tones which were preceded by either a pure tone or a linear FM pure-tone adaptor. The results of Gardner and Wilson [J. Acoust. Soc. Am. 66, 704-709(1979)] were generally confirmed: Thresholds were larger by about a factor of 1.7 when the adaptor and test sweeps rose in frequency. This increase in threshold corresponds to a change in performance from 75% to 65% correct. As an alternative to feature-selective channels, we propose that this small effect is due to nonsensory factors, specifically, the use of an adaptor-like reference in the "adapted" condition. Performance similar to that obtained in humans is shown by an ideal receiver that uses an inappropriate reference to match the signal in the detection task.     

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） system

From experimental results of spin polarized injection and transport in organic semiconductors(OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm’s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.     

频率可调谐的非经典光场的产生及其在FM光谱中的应用

利用Ⅱ类相位匹配KTP晶体组成的双共振OPO,实现了可调谐连续OPO单频运转,最大输出功率360mW,波长调谐范围大于9nm.在此基础上,进一步利用α切割KTP晶体获得了输出波长可调谐的强度关联孪生光束,调谐范围大于5nm,最大量子关联大于5dB.将此非经典光场用于Cs2频率调制光谱测量,获得了突破散粒噪声极限4dB的测量结果,在室温下观测到了Cs2在1041nm、1065nm的吸收谱.     

利用电光FM调制抑制零级中心频带——实现超高频Radio over Fiber通信

提出了一种有效抑制零级中心频带方案,并证实了该方案的可行性,给出了基于该方案的单工Radio over Fiber (RoF)通信系统.通过光通信系统软件Optisystem5.0仿真模拟结果显示：光源发送功率为5 dBm,途中无光放大,24 GHz的超高频微波信号在色散系数为20 ps/nm/km、衰减系数为0.25 dB/km的单模光纤中传输,系统码元传输速率可达5 Gbit/s、传输距离15 km以上.     

A 40 km Fiber－optic Microwave Subcarrier Multiplexing Transmission System for Multi－channel FM－TV

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The spin-1 Blume–Capel model on the Bethe lattice in ± J distribution with an adjustable parameter between FM and AFM phases

The spin-1 Blume–Capel (BC) model is studied on the Bethe lattice (BL) for the ?±? J distribution with a competing adjustable parameter α which alters the strength of bilinear exchange interaction parameter for the ferromagnetic phase (J?>?0) with respect to antiferromagnetic phase (J?<?0). The J?>?0 and αJ?<?0 values are also distributed throughout the BL with probabilities p and $1?p,$ respectively. The order-parameters are obtained on the BL in terms of exact recursion relations (ERR’s) and their temperature (T) variations are studied to calculate the phase diagrams on the (α, T) planes for given values of p, crystal field (D) and coordination number $q=3$ corresponding to honeycomb lattice. It is found that the model gives both first- and second-order phase transitions and also tricritical points. In addition to the well known ordinary phases and TCP’s, the spin glass phase and two more special points are also observed.