用于基带HDTV信号记录的1／2英寸盒式录像机

本文叙述最新研制的,用于记录基带高清晰度电视信号的1/2英寸盒式录像机的技术细节。它采用金属带和叠层非晶体视频磁头,记录时间可达63分钟,亮度和色度信号的带宽分别为20MHz和7MHz。为了克服传统分段记录的弊端,提出了一种新的二通道、三分段记录方式。     

MⅡ录像机简介

M Ⅱ录像机属高质量模拟分量记录格式,采用1/2英寸宽的盒式金属带,将一场复合的电视信号分离为亮度信号和色度信号分别经过调频后由两对旋转磁头在磁带上形成各自的磁迹,为了使两个色差信号R-Y,-Y记录在同一条磁迹上,又采用了时间压     

家用VHS录像机的维护

录像机是用来记录、重放图像和声音信号的。它与录音机虽具有相似的原理,但无论在机械部分还是电路部分都要比录音机复杂得多。因为图像信号的信息量远大于音频信号的信息量,所以录像机不能采用录音机那样的固定磁头来进行录放,而是采用旋转磁头来增加磁头与磁带的相对速度,以进行高密度的记录和重放,如图1所示。PAL制1/2英寸VHS盒式录像机的相对速度为484cm/s,磁带速度为2.339cm/s,磁头的旋转速度为1500r/min。为了确保磁带运动速度、磁头旋转速度的准确性,录像机内设有磁头鼓电机和主导轴电机伺服控制电路。     

MⅡ录像机的机械维修与保养

MⅡ格式录像机是日本松下公司在80年代初期推出的。它采用分量记录方式将亮度信号与色度信号分别进行处理，并记录在各自的磁迹上。MⅡ首先使用1／2英寸金属磁带，采用CTCM系统（色度信号时间压缩多工系统），共记录质量可以达到1英寸机的水平。目前美国NBC及日本NHK和世界上许多电视台都大量使用。     

MⅠ和Betacam—SP录像机

随着电视广播事业的发展，作为电视节日制作、编辑和播出的主要设备之一——磁带录像机也在迅速发展。从2英寸四磁头录像机到1英寸单磁头录像机，又从1英寸单磁头录像机发展到3／4英寸双磁头录像机，现在又出现了一种高性能、新格式的录像机，那就是1／2英寸双磁头录像机，其代表是MⅠ和Betacam—SP。MⅡ录像机是以日本栓下公司为主生产的，Betacam—SP是日本SONY公司生产的。自从这两种录像机问世以后，受到了各国电视台的重视。特别是1988年汉城奥运会后，     

一种用于数字录像机的垂直方位角记录方式

本文给出一种新型的垂直磁记录方位角单极磁头，并进行了读写试验。在此基础上讨论了垂直方位角记录方式用于数字录像机的可行性。结果表明：垂直磁记录方式有利于提高记录密度和降低邻道串音，有利于满足高清晰度录像机对存储容量的要求。     

3／4英寸录像机视频记录电流的佳化调整

更换视频磁头是录像机维修中最基本而又非常重要的项目，而记录电流又是其中关键的一步调整，它会直接影响所记录信号的重放射频（RF）电平和解调后的视频信噪比。     

录像机的记忆方式及其图像质量

录像机的记忆方式及其图像质量郭晓玲中国矿业大学电教中心众所周知，录像机是记录和重放视频信号的工具，视频信号通过录像机的磁头记录在录像磁带上，然后再通过磁头将信号重放出来，视频信号的记录方式与录制的信号质量密切相关，本文主要谈谈不同视频信号的记录方式与...     

国外消息

▲1/2英寸高清晰度录像机日立公司研制出一种与高清晰度电视广播兼容的1/2英寸录像机样机。这种录像机可记录150分钟。该机采用直径62mm的磁鼓,磁头记录20MHz宽带的亮度信号,另外两个磁头记录5MHz的色度信号。该机可给出43dB信杂比。录像机重放的图像分解力为650线。该机无需专用的解码器,它使用小的103.5×192×25(mm)带盒。样机的尺寸为500×465×150(mm)。     

磁带录像机的调频系统

在研制用磁带记录宽频带信号的设备时会碰到一些问题:象频率比50赫低得多的信号的传输过程,单位长磁带上之磁通量变化很慢,这种信号的重放电平将很低;如果频率高达几兆赫,主要的问题是使磁带上波长超过磁头的缝宽,这一点用提高带速或者减小磁头缝宽可以做到.为了能够经济地利用磁带并保证信号的带宽能令人满意地传输,在磁带录像机上采用调频方式传输图像信号.本文将叙述调频特性,残留边带传输方式以及介绍一些调制器和解调器的电路.     

HCS12单片机--融合8位/16位技术快闪单片机系列

尽管全球半导体市场发展放缓,但2001年国内芯片市场受强劲需求的带动,销售量和销售额仍分别保持了8％和29％的增长。国内单片机市场更成为电子工业领域备受关注的热点,2001年的微控制器销量已经达到7.79亿块,而预计2005年市场总需求量将大幅增长至18亿块。     

加盟单片机阵营的Motorola16位DSP

当今嵌入式系统应用可以分为控制和运算两大类.控制类应用主要由单片机(MCU)来完成,如各种工业控制应用;运算类应用则主要由DSP来完成,如MP3、MPEG等编码解码和音频视频的压缩解压缩等等.     

16位稳态电流LED驱动器的ASIC设计

提出了一种大电流16位稳态电流LED驱动器的ASIC设计方案,并描述了芯片的主要功能原理。对各个模块的主要电路进行了分析和设计,数字部分电路依靠成熟的FPGA平台验证,最大程度提高了电路可靠性;模拟部分电路通过分析和计算,确定不同参数,最后对整个方案进行了仿真。这种16位稳态电流LED驱动芯片可以完成对点阵LED显示屏的驱动,芯片外围电路简单、成本低、可靠性高。该芯片也适用于点阵LED屏等LED设备的驱动,应用十分广泛。芯片方案的各个部分都给出了详细的仿真结果,整个方案最后通过了T-Spice后仿真。     

Generation of random bits with accurate and reproducible statistical properties

The generation of "accurate" random bits is the key problem of the techniques which use random numbers. First the author establishes the accuracy requirements of a random bit generator for serial and parallel number generation. Then known methods are shown to be unsatisfactory for accurate applications. An accurate bit generator is proposed which provides a binary variable with equiprobable values within a 10^-4to 10^-5accuracy range.     

人工噪声辅助安全传输中的反馈比特数研究人工噪声辅助安全传输中的反馈比特数研究

本文主要研究了人工噪声辅助的多输入单输出（Multiple-input Single-output, MISO）物理层安全传输系统中的最小反馈比特数问题。论文对信道方向信息采用基于随机矢量量化（Random Vector Quantization, RVQ）的码本反馈方法,首先定量分析了RVQ量化导致的系统保密速率损失,充分考虑不同发送信噪比条件与量化误差的特点,推导出了所需最小反馈比特数的闭合表达式。分析表明为保持恒定的遍历保密容量损失,反馈比特数应随对数信噪比及(Nt-1)线性变化（Nt为发送天线数）。理论分析和仿真结果表明,依据本文得到的闭合表达式调整反馈比特数,可以满足系统的安全性能要求。现有研究没有考虑信噪比较低的情况,而本文的结论适用于各种信噪比情况,对于人工噪声辅助的物理层安全传输策略实用化具有指导意义。      

Chinese-character printer with electrostatic recording

Mechanical typewriting translators have been widely used for monitoring of Kanji (Chinese character) teleprinter system in newspaper companies despite their substantial disadvantages such as slow typing speed, poor stability, difficult maintenance, and mechanical noise. These disadvantages were completely solved by our electrostatic Kanji teleprinter (Fig. 1) which features high printing speed, reliability, and stability of operation.     

High-speed facsimile with electrostatic recording

Herein is reported a newly developed high-speed facsimile receiver for use over a wide-band transmission line of up to 48 kHz. The main feature of this equipment is low cost and high speed obtained by mechanical scanning. Good quality electrostatic recording has been achieved at a speed of up to 4000 line scans per minute. The circle-to-line converting multistylus made by printed circuit technology is used for the recording head. A single torsional spring-type rotating wire brush is driven directly by a high-frequency multipole hysteresis motor; thus good contact and smooth operation are obtained with light pressure at high scanning speed.     

解读8位MCU市场

大多数人以为，讨论8位MCU（微控制器）并不是个时髦的话题，它只是高于4位产品，上面还有16位和32位，所以它不过是个低端产品而已。然而，在整个MCU市场中，8位MCU市场仍然十分活跃，占据着绝对统治的地位，其销售额之大令人咋舌。专门从事半导体行业市场研究的Semico研究公司的技术总监TonyMassimini先生指出：“低端只是相对而言，今天的低端乃10年前的高端，而且今天的8位MCU并非昨日黄花。从产品需求量来看，8位MCU仍是主流，占有MCU市场销售总额的43%和发货量的60%。”他也认为，虽然低端MCU不是高速成长的市场，但经营者…     

Stealing bits from a quantized source

We consider "bit stealing" scenarios where the rate of a source code must be reduced without prior planning. We first investigate the efficiency of source requantization to reduce rate, which we term successive degradation. We focus on finite-alphabet sources with arbitrary distortion measures as well as the Gaussian-quadratic and high-resolution scenarios. We show an achievable rate-distortion tradeoff and prove that this is the best guaranteeable tradeoff for any good source code. This tradeoff is in general different from the rate-distortion tradeoff with successive refinement, where there is prior planning. But, we show that with quadratic distortion measures, for all sources with finite differential entropy and at least one finite moment, the gap is at most 1/2 bit or 3 dB in the high-resolution limit. In the Gaussian-quadratic case, the gap is at most 1/2 bit for all resolutions. We further consider bit stealing in the form of information embedding, whereby an embedder acts on a quantized source and produces an output at the same rate and in the original source codebook. We develop achievable distortion-rate tradeoffs. Two cases are considered, corresponding to whether or not the source decoder is informed of the embedding rate. In the Gaussian-quadratic case, we show the informed decoder need only augment the regular decoder with simple post-reconstruction distortion compensation in the form of linear scaling for the resulting system to be as efficient as bit stealing via successive degradation. Finally, we show that the penalty for uninformed versus informed decoders is at most 3 dB or 0.21-bit in the Gaussian-quadratic case and that their performance also lies within the 1/2-bit gap to that of successive refinement.     

Coherent MAP detection of DQPSK bits

Both IS-136 and PDC digital cellular systems employ forward error correction (FEC) encoding followed by a form of DQPSK modulation. In this letter, we derive the maximum a posteriori (MAP) bit detector for DQPSK modulation in non-ISI channels for a coherent receiver with one or more antennas. The MAP detector forms a bit log-likelihood ratio, which provides the optimal “soft information” for MLSE or MAP convolutional decoding. MAP detection requires exponentiation and logarithm operations, as well as knowledge of the noise covariance. To avoid these operations, two approximate forms are developed, which do not require the noise covariance value under certain assumptions. Both approximate approaches, when used with soft FEC decoding, are within 0.5 dB of the optimal approach