A simplified HF field strength prediction procedure for India

Field strength measurements of several HF broadcast transmissions were made at New Delhi during 1987-1990 with a view to evolving a simple procedure for estimation of the skywave field strength in the HF bands (3-30 MHz). An attempt has been made using the measured field strength values to arrive at a single combined loss factor which can account for all the losses in excess of basic free space and ionospheric absorption losses. The present study has shown that a provision of 4 dB for transmission losses other than free space and ionospheric absorption losses can bring the predicted values closer to measured field strength values for single-hop circuits in India for about 50% of the cases, and 10 dB increases it to 90%. Transmission losses in general were found to be much higher during equinoctial months in India, particularly around the peak region of equatorial anomaly     

Prediction of Medium-Frequency Skywave Field Strength in North America

Medium-frequency skywave propagation is a very complicated matter. As a result, it has been very difficult to predict the skywave field strength, particularly for propagation paths in North America. The existing method in the FCC Rules and Regulations offers reasonable accuracy only when the sunspot number is low. A more recent method proposed by CCIR Interim Working Party 6/4 works well for other regions of the world but displayed certain limitations when applied to propagation paths in North America. Its treatment of frequency is exactly the opposite to observations made from measurements taken in North America. Its treatment of solar activity is also oversimplified. A new method developed by this author mathematically takes care of the uniqueness of North American paths, consequently, better results have been obtained. This paper presents the derivation of the new method together with a comparative study of the three methods that are now available. Extensive FCC data has been used as a common base.     

24-Hour Neural Network Congestion Models for High-Frequency Broadcast Users

This paper presents the development of Neural Network models to predict the likelihood of interference experienced by Broadcast users in the HF spectrum (3-30 MHz). The models are based upon several years of measurements recorded at LinkÖping (Sweden) across the HF band, covering a substantial part of a sunspot cycle. The dataset used for the model development is a result of a long-term project being undertaken jointly by the University of Manchester and by the Swedish Defence Research Establishment, to measure systematically and to analyze the occupancy of the entire HF spectrum. The measure of occupancy used is congestion, which is defined as the fraction of channels within a certain frequency allocation with signals exceeding a given threshold. The procedures for measuring and modeling congestion as a function of solar activity, time of day, day of year and incident field strength threshold are briefly presented.      

An improved HF field strength prediction method

A multi-correlation process for reducing the RMS error between the field strength values predicted by the use of the method laid down in Report 894.2 (1991) and the values of Databank.D1 is described. Three functions are used. The first function has 1080 coefficients describing 10 distance ranges, 4 solar activity ranges, and 27 frequency to MUF ratio ranges. The second function covers 10 distance ranges and 24 local time data in the mid path with a total of 240 coefficients. The third function has 720 coefficients covering 10 distance ranges, 6 modified dip angle values, and 12 months. With the use of these functions, the final RMS error is 7.69 dB for the whole set of circuits of Databank.D1 database and 7.29 dB for short paths. The Report 894.2 method has a RMS error of 10.1 dB. Four plots are included to compare that method with the improved method     

Dielectric charging in silicon nitride films for MEMS capacitive switches: Effect of film thickness and deposition conditions

The paper presents a systematic investigation of the dielectric charging and discharging process in silicon nitride thin films for RF-MEMS capacitive switches. The SiN films were deposited with high frequency (HF) and low frequency (LF) PECVD method and with different thicknesses. Metal–Insulator–Metal capacitors have been chosen as test structures while the Charge/Discharge Current Transient method has been used to monitor the current transients. The investigation reveals that in LF material the stored charge increases with the film thickness while in HF one it is not affected by the film thickness. The dependence of stored charge on electric field intensity was found to follow a Poole–Frenkel like law. Finally, both the relaxation time and the stored charge were found to increase with the electric field intensity.     

Propagation Characteristics of an Elliptically-cored Highly Birefringent Fiber using an Analytical Method

By using the method of separation of variables in the elliptical coordinate system, a representative formula in terms of Mathieu and modified Mathieu functions is derived and longitudinal field components for the even and odd modes are presented for the proposed fiber. The eigen value equation for the fiber to be considered is obtained by solving the fourth order determinantal equation under weak guidance condition and is given in this paper. The cutoff frequency of several lower orders modes for different eccentricities have been obtained and their propagation characteristics have been plotted. The effect of the eccentricity on the modal cutoff values and mode transmissions is discussed. Finally, the modal birefringence in the proposed fiber is also estimated.     

Mobile radio propagation path loss studies at VHF/UHF bands inSouthern India

Field strength measurements at 200, 400 and 450 MHz (VHF/UHF band) were conducted with the field strength meter placed on board a vehicle in Southern India. Observed field strength values were converted into path losses and are compared with different path loss prediction methods like Hata (1980), Egli (1957), Blomquist-Ladell (1974), COST 231 Walfisch-Ikegami (Doble 1996), Walfisch-Bertoni (1988) and ITU-R. These path loss studies are carried out in urban, suburban and open areas in this region. The results showed that Hata's method gave better agreement with observed values in urban, suburban and open regions; the COST 231 Walfisch-Ikegami model is also in good agreement with the observed values in urban and suburban regions, the Egli and Blomquist-Ladell methods showed moderate agreement in open regions only. The agreement of the Walfisch-Bertoni and ITU-R methods with observed values is not good     

Comparative study of field strength prediction methods in medium wave band

Recently developed digital radio systems for the medium wave band require accurate field strength prediction algorithms for coverage estimation. Presented is a comparison of estimation accuracy provided by the most relevant field strength prediction methods employed for ground-wave propagation at this band. Moreover, a field strength prediction method recently developed by the authors, has been considered in the analysis. Empirical values from measurement campaigns carried out in three different broadcasting networks have been used to analyse the accuracy of the prediction methods. Comparison between predicted and measured values allows objective evaluation of the estimation accuracy of each method under different reception conditions. The proposed method provides the most accurate results on field strength predictions, consequently it is a suitable method for the coverage estimation of the new digital radio systems.     

Effects of surface preparation on the electrical and reliabilityproperties of ultrathin thermal oxide

A new wafer cleaning procedure has been developed for ultrathin thermal oxidation process (⩽50 Å). It consists of a conventional RCA clean and a two-dip step, first in diluted HF and then in a methanol/HF solution, with no final DI water rinse. The effectiveness of this cleaning process has been compared to other commonly used cleaning methods, based on the dielectric integrity of the ultrathin thermal oxide grown. It has been found that this two-dip method produces oxides with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxide. Furthermore, this new procedure increases dielectric breakdown field, E_bd and charge-to-breakdown, Q_bd (both intrinsic and defect-related values) of ultrathin oxides. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen and the reduced surface micro-roughness     

浅淡高频铝基板孔金属化加工工艺

孔金属化高频铝基板是一种特种印制板，其具有高频印制板频带宽、信息量大，传输速度快和铝基印制板强度高、散热性好等优点，近年在混合集成电器、大功率电气设备、电源设备等领域得到了广泛应用，本文就孔金属化高频铝基板的生产加工进行交流。     

Solar activity and MF skywave propagation

An examination is made of the effect of solar activity on MF skywave propagation, and quantitative expressions describing the effect are presented. It is shown that these equations are valid for all latitudes and for the two commonly used reference hours, two and six hours after sunset. Until recently, it has been assumed that the effect of solar activity was more or less the same for all hours of the day. However, the studies reported show that the effect is the greatest during the hours from sunrise to two hours after sunset. During these hours, the reduction of field strength is a function of sunspot number, geomagnetic latitude, path length and frequency. Beginning at two hours after sunset, the effect diminishes with time, reaching a minimum at about six hours after sunset. At six hours after sunset, frequency ceases to be a factor     

The effect of solar and geomagnetic activity on ionosphericpropagation

This report studied the effects that solar and geomagnetic activity has on ionospheric propagation. The goals of this study were to identify solar emissions that help and hinder high frequency broadcasting and to determine how much the signal strength and, the maximum usable frequency of the one-hop and two-hop F2 mode decreased during disturbed propagating conditions. A series of measurements were taken using the calibrated antenna and receiver system (CARS) during the month of February 1994 in order to show the differences between ionospherically disturbed and undisturbed days. Research from previous reports and text books were used to clarify the data. Although a decrease in signal strength for this experiment could not be tied to solar and geomagnetic activity, the change in the daily maximum observable frequencies scaled from the recorded ionograms shows a strong correlation. The data collected shows that the usable frequency band becomes limited on disturbed days. Additional data should be collected for extended periods of time and analyzed in the same manner as outlined in this paper to develop a plan for the worst case scenario in order to guarantee successful propagation     

Ground wave propagation over a mixed path with an elevation change

Calculations have been performed for high frequency (HF) ground wave transmission over a mixed path with an abrupt elevation change. The effect of the elevation change is to decrease the field strength at large distances.     

Path delay, its variations, and some implications for the field use of precise frequency standards

In order to assess the practical utility of high-performance frequency standards in field applications, the effect of the propagation medium must be taken into account. After a brief summary of noise processes, a discussion of the performance of current frequency standards is given, together with an estimate of the relative cost, reliability, and necessary system support for each type. Literature references on atmospheric physics are given to allow determinations of those limitations which the earth's atmosphere and ionosphere impose on the transfer of precise frequency and time. Formulas are presented to estimate the effects of changes in temperature, pressure, humidity, and frequency on the propagation path of electromagnetic waves. Current methods used to compute the path delay for HF, VLF, Loran-C, and other precise frequency transmissions are given. Based on this material, we outline needs for future frequency control capabilities.     

一种用于无线信道的逐幸存处理均衡器

提出了一种适用于无线时变信道的逐幸存处理均衡器。通过训练序列得到信道参数的初始估计值,此后在Viterbi算法进行网格搜索的过程中,使得每一条幸存路径维持各自的信道参数,并在确定幸存分支后利用历史幸存序列对信道参数值进行更新,实现了信道参数的无时延估计。仿真结果表明,在无线时变信道环境下,逐幸存处理均衡器的性能明显优于其他传统均衡器。     

Electromagnetic shielding of HF lamps using wire structures:simulation and measurement

High-frequency (HF) operated lamps, such as HF fluorescent lamps, have several advantages over conventional ones but they contaminate the environment with their EM field emissions. The shielding of the electromagnetic emission should be realized without much effect on the emission of the light. Enclosing the lamps in a housing made of widely spaced thin wires could be an appropriate way to shield the electromagnetic field. The paper studies the effectiveness of some wire structures for shielding the electromagnetic emission from HF fluorescent lamps. An analytical study, method of moments (MoM), and measurements have been carried out to evaluate the strength of the near-field and the shielding effectiveness of the structures     

Comparison of measured and predicted field strengths of medium frequency sky waves over short distances in Japan

Nighttime sky waves of four medium frequencies were observed at distances of not larger than about 300 km in Japan for one to two years of high and low solar activities. The sporadic E (Es) layer always appeared with high probability. Analyzing these data, the following results were obtained: 1) the measured median field strengths are different by at least more than 7 dB from full wave predicted values for the international reference ionosphere (IRI) without the Es-layer. But these agree fairly well with the full wave calculation for IRI with the Es-layer, 2) the field strength approximates the Rayleigh distribution, 3) according to the data for high solar activity, the sky wave appears rapidly after sunset, and during the two to six hours after sunset all median field strengths are about constant.     

高频雷达工作频率优选方法研究

高频雷达能够实现对视距外目标的探测和跟踪,有广泛的军事应用前景.随着高频雷达的不断发展,雷达工作频率优选方法成为一个重要研究课题.提出了基于信杂比最大的高频地波雷达工作频率优选准则,并对准则中的地波传输损耗和目标的雷达截面积与雷达工作频率的关系进行了讨论,最后得出频率优选方法.该方法能够针对不同类型的探测目标选出雷达最优的工作频率,对高频雷达设计和运用具有指导意义.     

电离层人工调制的极低频辐射和在潜艇通信中的应用探讨

本文分析被调制的高频波加热电离层所产生的极低频辐射过程和极低频在地球-电离层波导中的传播模式,以及应用于潜艇通信中的可能性。数值结果表明,如果高频有效发射功率为100MW量级,频率为5MHz,调制频率为100Hz,则准TEM模式在地球-电离层波导中传播的衰减率一般小于1dB/Mm,距加热地点1000km处海面(地面)上磁场强度的量级为10-8A/m。对于潜艇通信,在辐射源强度确定的情况下,对不同的潜艇深度和通信距离,存在一个最佳选择频率。     

Potential effects of broadband wireline telecommunications on the HF spectrum

Power line telecommunications and various forms of digital subscriber line transmissions are recent and rapidly evolving technologies using the existing electricity power or telephone lines for data transmission at rates higher than 1 Mb/s. As these lines were not designed for transmission of high data rates, they produce noiselike interferences in the HF range. The intensity depends on the electrical characteristics of the lines (balance, match, screening) as well as on the density and area coverage of these new systems. Exact calculations are impossible at this time because of missing models for the new wirebound communication systems with respect to emission of radio noise in the HF band. Early measurements and estimations showed that radio noise from PLT and xDSL has the potential to cause problems for military HF radio communications and communication intelligence. A Research Task Group under NATO was assigned to study the issue and determine possible solutions. Briefly, the findings of the RTG do indicate that PLT emissions have the potential to cause appreciable degradation in the exploitation of the HF spectrum by military users.