振荡限幅器型卫星电视接收解调器

本文分析了振荡限幅器的基本工作原理及工作条件，并设计了一种振荡限幅器型卫星电视接收解调器。同时将其用于接收苏联７１４ＭＨｚ卫星电视。实验表明，该解调器性能良好，门限改善量可达３ｄＢ以上。     

新型卫星电视门限扩展解调器—FPLL

FPLL是一种新型卫星电视门限扩展解调器。与常规PLL门限扩展解调器相比,它具有捕获范围宽,捕获时间短,门限改善量显著等优点。本文首先介绍FPLL的工作原理,然后对FPLL进行初步理论分析。     

锁相接收信道寄生调制对测距精度的影响

在锁相测距信道中,当接收信号低于某一电平后,测距漂移误差显著地增加。这种现象称为“测距漂移误差门限”效应;对应的电平,称为“测距漂移误差门限”电平。本文阐述了这种“门限”效应产生的物理过程及其数学表达式。讨论接收信号电平变化时,信道的寄生调制对测距漂移误差的影响。分析了信道中几个主要部件,如带通滤波器、中频放大器、限幅器、解调器等对测距漂移误差所起的作用。保持接收信道频率特性的对称和解调器的正交,采用小信号限幅,可以减小奇生调制,提高测距精度。     

四米天线卫星电视接收站

四米天线卫星电视接收站,是邮电部第四研究所研制的最新产品,全套设备由四米天线(卡塞格伦双反射抛物面天线)、下变频器、电视体音解调器部分组成。它采用80K场效应低噪声放大器和二次变频方案,下变频器稳定可靠并满足十二个频道技术指标要求,电视解调终端使用该所自行研制的门限扩展解调器,使卫星电视接收效果有明显提高,视频加权信噪     

卫星电视接收站的视频信噪比测试

本文给出C频段6米、4.5米、3米天线的卫星电视接收系统的视频信噪比的测试结果与分析。一、视频信噪比的关系式卫星电视接收系统的视频信噪比,是卫星电视信道线路传输质量的综合效果反映。在调频制卫星电视接收站中,为了保证接收质量,其解调器都工作在门限电平以上,此时视频信号功率S_v和噪声功率N_v之比     

可变副载频伴音解调器

介绍了一种用于卫星电视接收系统的可变副载频伴音解调器,并给出了整个解调器的设计框图及主要部分的电路原理、计算以及测试结果和结果分析。     

浅谈数字卫星电视接收系统的抗噪声性能

从数字卫星电视接收机的R-S解码器、卷积解码器和QPSK解调器等部分电路对系统抗噪声性能方面，对数字卫星电视接收系统的性能进行分析。     

卫星电视接收机的工作原理（5）频率解调器分析

（上接第２０期） 从卫星电视调频信号中取出电视基带信号,必须采用频率解调器（鉴频器）。鉴频特性可用“Ｓ”型曲线表征,它表示在一定的频率范围内鉴频器输出的电压基本上单调地与输入调频信号相对于中心频率的频偏成正比,此频率范围即为鉴频带宽,它应略大于接收机中放的带宽。 卫星接收机的频率解调器,通常分为常规鉴频器和门限扩展解调器。１ 常规鉴频器 在调频卫星电视接收机中,常用平衡鉴频器、移相鉴频器和桥式鉴频器。１．１ 平衡鉴频器 平衡鉴频器也称双失谐回路鉴频器,是由单失谐回路鉴频器发展而来,克服了灵敏度、线性和…     

发展中的我国卫星电视接收技术

本文综述了我国卫星电视接收的发展情况，论述了当前卫星电视接收中的关键技术－超低噪声高频头和一体化高频头，低噪声天线和天线的小型化，多制式微处理器控制的低门限接收机，多星广播的接收和多波束天线，卫星电视信道的综合利用。     

光折变晶体内的光振荡和光学限幅器

提出了一种利用光折变晶体光振荡的光学限幅器,在SBN晶体中得到了口字型和8字型光振荡通路,给出了光振荡的阈值条件以及作为光学限幅器的透射率与耦合系数的关系,并讨论了控制光振荡形式以改变限幅器性能的途径。     

On Optimum Sampled-Data FM Demodulation

Since the introduction of large-scale integration (LSI) techniques, there has been a continuing effort to develop digitalization techniques for communication equipment amenable to LSI implementation. Hopefully, this will permit expanded capability in the equipment while taking advantage of the cost reliability attributed of LSI. In this paper, a digitalized or sampled-data FM demodulator recursive algorithm is synthesized and its signal-to-noise ratio performance compared with the optimum analog demodulator and the conventional limiter discriminator demodulator. The demodulator is shown to exhibit threshold extension capability and automatic time-varying gain (bandwidth) adjustments from acquisition through tracking of the incoming modulated signal.     

The Capture Effect in FM Receivers

In this paper a theoretical explanation of the capture effect is given by calculating the instantaneous frequency of the output signal of a limiter when two frequency modulated (FM) signals are present at the limiter input. When this signal is applied to a demodulator with unlimited bandwidth, the output signal of the demodulator proves to have an extreme capture effect. When however the demodulator bandwidth is limited, the capture effect is shown not be be extreme. This phenomenon is explained and possibilities are given to minimize the capture effect. Some of the results of measurements on limiters and demodulators are given in this paper; they prove that a weak capture effect can be obtained. A method of calculating the degree of capturing is included.     

Broad-Band TEM Diode Limiting

The bandwidths of two types of limiters operating below diode resonance and one type of limiter operating at diode resonance are calculated. A 2.5-Gc base-band limiter was made providing a low power insertion loss of less than 1 db, a limiting threshold of 10 mw, and a high power isolation of greater than 20 db. A 0.9-to 1.3-Gc matched limiter was made having a VSWR of less than 1.2 for all power levels. The burnout power of these two limiters was calculated to be about 10 watts incident CW power or 1500 watt-microsecond incident pulse energy. Using the diode resonance the calculations indicate that it is possible to make a 5-Gc limiter with 15 per cent bandwidth, less than 1-db low power insertion loss, a limiting level of 10 mw, and greater than 20-db isolation at high power. The bandwidths derived for diode limiting are equally applicable to switching.     

Passive Phase-Distortionless Parametric Limiting with Varactor Diodes

The theory of passive parametric limiting with a varactor diode as the nonlinear element is developed and verified experimentally. The limiting is found to be flat and phase-distortionless. Expressions are given for threshold level, dynamic range, bandwidth, and power dissipation. The transient phenomena, comprising leading- and trailing-edge leakage spikes, are studied theoretically and experimentally, and found to be small in typical instances. Experimental results reported upon include a simple waveguide limiter structure at S band; a lumped-circuit limiter at 126 Mc; and a strip-line limiter using a pill varactor at S band. The latter has an insertion loss of 2.5 db below threshold, a threshold level of 2 mw, a dynamic range in excess of 20 db, and less than 5° of phase distortion. Agreement between theory and experimental results is excellent.     

Switched-capacitor FSK modulator and demodulator in CMOS technology

A switched-capacitor FSK modulator/demodulator built in silicon-gate CMOS technology is described. The modulator is based on a programmable harmonic oscillator using two stray-insensitive integrators. The centerpiece of the FSK demodulator is a switched-capacitor voltage-controlled oscillator. A simple post-detection processor restores the digital data. Both circuits have been designed for the 600-baud modem channel with 1500 Hz center frequency and /spl plusmn/200 Hz frequency shifts, but the demodulator operates in the 1200-baud channel as well. Due to dynamic biasing the operational amplifiers feature high slew rate, high voltage gain, and low power for capacitive loads.     

A Fully Integrated 0.13 μm CMOS Low-IF DBS Satellite Tuner Using Automatic Signal-Path Gain and Bandwidth Calibration

This paper presents the first low-IF fully integrated receiver for DBS satellite TV applications realized in 0.13 mum CMOS. A wideband ring oscillator based frequency synthesizer having a large frequency step was used to downconvert a cluster of channels to a coarsely defined low-IF frequency, while the second downconversion to baseband was performed in the digital domain. Eliminating the oscillator inductors reduced the parasitic magnetic coupling from the digital core, allowing a single-chip integration of the sensitive tuner and the noisy digital demodulator. A significant die area reduction was achieved by using a single oscillator to cover the entire satellite TV spectrum, while a noise attenuator was cascaded with the PLL loop filter to reduce the equivalent tuning gain. The low-IF architecture allowed a discrete-step AGC that improves both tuner noise and linearity performance. Tuner gain and IF corner frequency were calibrated using replica ring oscillators that are tuned up to the onset of oscillations. The tuner specifications include: 90 dB gain range, 9 dB noise figure at max gain, +25 dBm IIP3 at min gain, 1.3degrms integrated phase noise, les50 dBc spurs, 0.7 W power consumption from dual 1.8/3.3-V supplies, and 1.8times1.2 mm ² die area     

Evaluation of Chaotic Demodulator for EBPSK Signals

Based on the theory of Duffing oscillator weak signal detection and the technology of extended binary phase shift keying (EBPSK) modulation, the chaotic demodulator using the Duffing oscillator for EBPSK signals was proposed. The proposed demodulator could avoid the problem of demodulation filters design, and shows the excellent anti-noise capability of chaotic oscillator detection. Numerical and experimental tests were taken to investigate the impact of modulation parameters τ and θ on bit error performance of the proposed method, and the performance limits were gotten. The results show that the proposed chaotic demodulator works well under a very low signal-to-noise ratio (SNR) conditions, and gets SNR gains about 20 dB to 30 dB from the impulse filter.     

AM suppression with low AM-PM conversion with the aid of avariable-gain amplifier

This paper proposes the use of a variable-gain amplifier instead of a hard limiter for amplitude modulation (AM) suppression with low AM-PM (phase modulation) conversion. A hard limiter shows phase shift variations through input-amplitude dependent changes in output waveform, combined with bandwidth limitations. It is shown that these can be kept small only for limiter bandwidths much larger than the input frequency. A linear amplifier with variable gain used for AM suppression does not suffer from this problem. A CMOS variable-gain amplifier with gain-insensitive phase shift has been designed for this purpose. The benefits and limitations of the technique are explored with reference to an experimental 2.5 μm BiCMOS chip for a television IF demodulator. Experimental and simulation results indicate that the AM-PM conversion can be kept below 0.5° at 40 MHz over an input amplitude range of 20 dB, where typical hard limiters show 3-5°. This is achieved with an amplifier bandwidth of 80 MHz, while a hard limiter would need a bandwidth of more than 600 MHz to obtain similar results     

Demodulation of suppressed signals

A demodulator is proposed that exploits the by-produced image of a weak signal, which is suppressed by a strong interfering one in a bandpass limiter, to recover 3-dB from the well-known 6-dB weak-by-strong-signal suppression effect.