VHF Region Research Articles

ON THE STUDY OF EMPIRICAL PATH LOSS MODELS FOR ACCURATE PREDICTION OF TV SIGNAL FOR SECONDARY USERS

Demand for wireless communication technologies and systems keep increasing and has reached the peak where the capacity can only be achieved by improving spectrum utilization. The spectrum allocated to TV broadcast systems can be shared by wireless data services through exploiting spatial reuse opportunities (Spatial TV white space). Path loss models are used extensively in signal prediction, coverage optimization and interference analysis. Recently it is being used in estimating distances for safe operation of secondary users in TV white space. Peculiarities of these models give rise to high prediction errors when deployed in a difierent environment other than the one initially built for. It is however not very clear which model gives the best flt and what the penalties are for using the models outside the intended coverage area. In this paper, we assess the fltness of nine empirical widely used path loss models using flve novel metrics to gauge their performance. In order to achieve this, fleld strength measurements were conducted in the VHF and UHF regions along six difierent routes that spanned through the urban, suburban and rural areas of Kwara State, Nigeria. A program was developed in VB 6.0 language to compute the path losses for the empirical models. The measurement results were converted to path losses and are compared with the model's prediction. The results show that no single model provides a good flt consistently. However, Hata and Davidson models provide good fltness along some selected routes with measured RMSE values of less than 10dB. ITU-R P.1546-4, Walflsch Ikegami (WI),

On some important characteristics of VHF radio-emission associated with large extensive air showers

Experimental studies of radio-emission are done at 110 MHz and 220 MHz frequency in the VHF region using sophisticated detection and data acquisition system. Results obtained on i) frequency spectrum and lateral distribution of field strength, ii) variation of field strength (E) with height of shower maximum (Hm), iii) frequency distribution of depth of shower maximum (Xm) are presented and are compared with theoretical calculations. An attempt is made to estimate primary mass composition by radio method.

Recent Translocation of Variable and Diversity Segments of the Human Immunoglobulin Heavy Chain from Chromosome 14 to Chromosomes 15 and 16

We studied the organization and origin of three orphon regions, VH-F, D5-a, and D5-b, of the human immunoglobulin heavy-chain gene using yeast artificial chromosomes. VH-F and two D5 regions were mapped to chromosome bands 16p11 and 15q11-q12, respectively, by using human/rodent somatic cell hybrids and fluorescence in situ hybridization. No D5 segments were found on chromosome 14, in contradiction to previous reports. The VH-F region consists of 7 VH segments and encompasses 160 kb of DNA. A cluster of VH segments homologous to the VH-F region orphons was found in the region 245-430 kb (V2-26 to V3-11) upstream of the JH cluster on chromosome 14. Comparison of VH sequences between the VH-F and the chromosome 14 loci indicates that the translocation of the VH-F region took place, at the earliest, 20 × 106 years ago. The D5-a and D5-b regions were obtained in two independent contigs. The former contains only D segments in 140 kb of DNA, while the latter carries 3 VH segments downstream of D segments in 110 kb of DNA. V54, one of these VH orphon segments, is about 95% homologous to V1-18, which is located within the putative ancestor of the VH-F region on chromosome 14. Furthermore, the region detected by two DNA probes flanking the V54 segment was found only in the proximity of V1-18 within the 0.8-Mb VH region on chromosome 14. These results suggest that the two orphon loci on chromosomes 15 and 16 may have been translocated simultaneously.

RING: An integral equation algorithm for HF‐VHF radio wave propagation over irregular, inhomogeneous terrain

A modification in the mathematical derivation of an integral equation for propagation over irregular, inhomogeneous terrain and a numerically stable algorithm, RING, is developed to extend the frequency range of program WAGNER to frequencies in the VHF region. The solution to the integral equation is compared to residue theory and Fock theory and excellent agreement is obtained.

Organization of variable region segments of the human immunoglobulin heavy chain: duplication of the D5 cluster within the locus and interchromosomal translocation of variable region segments.

We have studied the organization of variable region (V) genes of the human immunoglobulin heavy chain (H) by cosmid cloning. We isolated two independent immunoglobulin D5 clusters (D5-a and D5-b) from cosmid libraries of the human genome. Restriction maps of these two regions showed that downstream 15 kb portions of the 55 kb overlap were different although upstream 40 kb portions were almost identical. Four more D segments, (DM, DXP, DA and DK) were found around the D5 segment in the conserved region of each cluster. Nucleotide sequences of the corresponding D segments from each cluster were almost identical and they encoded potentially functional D regions. Analysis using human-rodent somatic cell hybrids demonstrated that both clusters were located in the immunoglobulin heavy chain (H) locus on chromosome 14, suggesting that the D5-a and D5-b regions evolved by internal duplication within this locus. We also isolated a 60 kb DNA region carrying four VH segments, designated as VH-F region, which was located on chromosome 16. Nucleotide sequences of the four VH segments were determined. Two of them encoded potentially functional VH segments, and the other two were pseudogenes. Some more VH segments were found to be located outside chromosome 14, by Southern blot hybridization of human-rodent hybrid cell DNAs. These results provide further evidence that the human VH locus has undergone recent reorganization.

Temperature‐stabilization of lumped‐element circulator in VHF region

AbstractPerformances of VHF lumped‐element circulators change sensitively by slight changes of 4πMs of garnets with temperature. Single‐tuned 100‐MHz circulators are studied. One experiment is to measure changes of external fields under the constant frequency condition with temperature; another experiment is carried out under the constant impedance condition. The former agrees well with theoretical predictions; the latter shows poor agreement.The parabolic compensation, which is the addition of several kinds of compensator alloys to magnetic circuits in parallel or in series depending upon the convex‐shape temperature characteristics of 4πMs, is very useful.

Optical Excitation of Zeeman Coherence in Ruby

Optically induced Zeeman coherences between various pairs of sublevels in the ground state 4 A 2 of a sample ruby (0.05 wt.%) were observed at room temperature by using impact excitation with circularly polarized resonant light pulses from a mode-locked ruby laser. The precessing magnetization associated with Zeeman coherence was detected magnetically in UHF, VHF and X-band microwave regions. The observed signals can be regarded as various types of ESR free induction decay signals and the decay times were of the order of nanosecond. Sustained precession signals were also observed. Characteristics of the signals were explained by numerical solutions of the Liouville equation.

Power DMOS for high-frequency and switching applications

The virtues of DMOS over other MOS technologies are first presented. The design considerations for the device are then given. Device fabrication and characteristics are also shown. With the data from these devices, a small-signal low-frequency model is derived which incorporates velocity saturation. The high-voltage breakdown is considered and an analysis of both the theoretical and experimental values are compared. Both punchthrough and avalanche breakdown of the DMOS device are discussed. The device has exceptional power gains in the VHF region considering its simplicity in design rules. A high-frequency linear model is constructed and is valid up to several gigahertz. Several improvements are proposed involving more strigent design rules which should yield power gains in the gigahertz region. With the process presented in this paper both high-frequency performance and high-voltage breakdown are obtained.

Improving the Frequency Characteristics of RF Standard Magnetic-Field Generator Employing Loop Antenna

In the HF and VHF region, the standard magnetic-field generator having a loop antenna has been generally used for the calibration of a radio receiver or a field-strength meter. Presented are new standard magnetic field generators which are able to produce a constant magnetic field over a wide band frequency range by means of measuring the loop current through a compensation transmission line and a compensation thermination resistor. A magnetic-field generator in which a thermistor was used as both a compensation resistor and a current sensor was constructed and examined over the frequency range 10 to 50 MHz. The measured values were agreed with theoretical values within ±0.1 dB.

On the electromagnetic field of a dielectric coated coaxial cable with an interrupted shield

A boundary value treatment is used to derive field expressions for a dielectric coated coaxial cable with a gap in the shield. Specific results are given for an incident TEM mode in the interior coaxial region. For example, it is shown that, for the VHF region, as much as 18 percent of the incident power is radiated into the external region via a single circumferential gap in the shield. Comparable amounts of power are transferred to a reflected TEM mode in the cable and into surface waves in the dielectric jacket.

磁電効果素子を用いた高周波広帯域電力測定

磁電効果素子を用いた高周波広帯域電力測定

The impulsive radio noise environment at a quiet site

In a search for a suitable site for the detection of cosmic ray air showers by radio, measurements of the fast pulse background in the VHF region of the spectrum have been made at two sites. These were a semi-rural site (Jodrell Bank) in S.E. Cheshire and a remote site (Hafren Forest) in mid-Wales. It was found that the vast majority of pulses were caused by man-made interference, only a small proportion being due to natural phenomena. The rate of arrival of such pulses is likely to be very low in a suitably remote site.

Vhf Pulsed Magnetic Resonance Duplexers

Coupling schemes for pulsed magnetic resonance spectrometers operating in the vhf region are discussed. Three such schemes are described in detail and their performances compared, using the 81Br nuclear quadrupole resonance signal at ∼200 MHz in polycrystalline K2PtBr6. The first scheme employs a hybrid T, coaxial ring circuit with the transmitter, receiver, sample coil, and a dummy load in the four arms. Series and shunt PIN diode switching elements form the basis of the second scheme proposed. Finally, a PIN diode bridge which combines the previous two schemes is described.

Ferrites for permeability tuning in the VHF region using the above resonance mode

The above resonance mode for obtaining and varying permeability in the VHF region is described. In this mode the bias field and RF magnetic field are orthogonal, and the ferrite core is always saturated or close to saturation. The bias field is larger than that required for ferromagnetic resonance. Eleven ferrites were evaluated with respect to operation in this mode. Tests included the determination of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> as a function of permeability, the temperature coefficient of permeability, and the effects of high RF flux densities on the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> of the ferrite. Application in the above resonance mode results in considerably higher permeability and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> values than the conventional approach at frequencies above 50 MHz. In addition, the RF power handling capabilities are substantially increased.

Admittance Bridge Determination of Quartz Vibrator Parameters Using Augmenting Immittance Elements

Bridge methods are the most accurate means of determining the parameters of quartz vibrators, particularly in the VHF region and above. Present and future crystal requirement specifications point to the increasing use of such methods to obtain the accuracy necessary for both filter and oscillator applications. A practical difficulty that arises is that the ranges of any given bridge are not compatible with every immittance characteristic encountered with the various crystal types in use, particularly if measurements are to be made over substantially different portions of the region of resonance. One means of obviating this difficulty is to augment the crystal with another impedance element in series or parallel so that the behavior of the combination is accommodated within the bridge ranges. A capacitance in parallel with the crystal is suitable for reducing the variation in impedance bridges that consider the unknown as a series combination of resistance and reactance; a series element reduces the variation in admittance bridges that represent the unknown as a conductance and susceptance in parallel. The purpose of this paper is to discuss the applicability and limitations of this latter procedure and to describe how the crystal parameters are extracted from measurements of this type.

Design of a VHF Suppressed Antenna

The paper presents the design details and the experimental results of an E-fed cavity type suppressed antenna for operation in the VHF region. Empirical formula has been derived for critical dimensions. The radiation pattern of two antennas back to back is omnidirectional.

Maximum RF power transistor collector voltage

The RF operating voltage of power transistors designed for operation in the HF, VHF, and UHF regions has been found to be greater than previously realized. This higher operating voltage is attributed to the slow response of the device surface with respect to the operating frequency of the circuit. Since most devices have breakdown voltages which are initially surface limited, their voltage operation at the higher frequencies is superior to the 60-cycle curve tracer behavior.

Some RF Characteristics of Bonding Systems

The measurement of bonding impedance has been typically limited to dc or to relatively low (<20 MHz) frequencies. However, the impedance characteristics of the bonding system should not be simply ignored at higher frequencies. To do so may be neglecting a serious source of electromagnetic interference. This paper presents techniques for the measurement and interpretation of bonding impedance characteristics through the VHF region. A measuring device based on the insertion loss technique is described. Calibration curves of typical models of this device show its usefulness for measurements up to 400 MHz. The application of this device to the measurement of bonding systems in field installations is also explored. From data obtained with the insertion loss device, an equivalent circuit of a typical bonding system is developed which incorporates the contributions of the equipment case as well as those contributions of the bonding straps to the overall impedance characteristics. It is shown that typical bonding systems exhibit regions of parallel resonance which are often at relatively low frequencies. Within these regions, the impedance of the bonding path is often very high. Because of this high impedance, the equipment case can act as a very effective antenna. Evidence is presented to show that the case voltages induced by a radiated field in the resonant frequency region may increase as much as 25 dB for a bonded system over a system that is not bonded.

Method of achieving gyrator realizations in the HF and VHF regions

Method of achieving gyrator realizations in the HF and VHF regions

An investigation into transistor cross-modulation at VHF under AGC conditions

The cross-modulation behavior of a transistor is studied for the case where it is operated in the VHF region and gain control is effected by driving it into saturation. It is shown that the observed increase in cross-modulation can be attributed to the fact that in the saturated condition the stored charge in the transistor will depend noulinearly on the collector current. The cross-modulation factor is calculated assuming an arbitrary functional relation between stored charge and current. A relation between the cross-modulation factor and the change of the cutoff frequency with current then will exist, allowing experimental verification. Close agreement is found between measured and calculated values.