Radio Interference Level Research Articles

Altitude Correction of Radio Interference of HVdc Transmission Lines Part II: Measured Data Analysis and Altitude Correction

The prediction and control methods of radio interference (RI) for HVdc transmission lines passing through high-altitude region are main key factors in design of the HVdc transmission lines. In order to obtain the altitude effect and correction of RI for HVdc transmission lines, four HVdc reduced-scale test lines with the same parameters were built up at 50, 1700, 3400, and 4300 m elevation, respectively. Simultaneously, two HVdc full-scale test lines with the same conductor type of 4 × JL/G1A-500/45 had been set up at altitude 50 and 4300 m as well, respectively. Using these test facilities, a lot of RI measured data were accumulated in a long time span, from Jan. 2010 to Jul. 2014. By analyzing the RI measurement data at different altitude regions, it is indicated that the altitude correction of RI has a nonlinear relation to the altitude. Meanwhile, the RI altitude correction formula for HVdc transmission lines has been proposed in this paper. Using the proposed RI altitude correction formula, the RI levels at high altitude are lower than that predicted by using the RI correction formula of ac transmission lines, which means that it could save a lot of investments at high altitudes.

Influence of altitude on radio interference level of AC power lines based on corona cage

To investigate the effect of altitude on radio interference (RI) of AC power lines, a corona cage test system was used to measure the RI excitation function values of different bundle conductors in different altitude locations, such as Wuhan 23 m, Jingyuan 1408 m, Xining 2261 m, Gonghe 2943 m and Yangbajain 4300 m. Then, the RI curves with different altitudes, bundle numbers and subconductor diameters were obtained. The analysis and comparison show that the actual RI altitude correction values fall in between the range of 1 dB/300 m and 40(1 − σ/σ 0) when the altitude below 3200 m, which is widely used as Italian correction term and Westinghouse correction term, respectively. Above this altitude, they are not applicable to predict the correction values. In this study, an RI correction term is proposed from the test results, which are fitted well for different altitude regions <4300 m.

Radio interference excitation function of conductor bundles based on cage test results and comparison with long‐term data

A reasonable excitation function is vital to make a precise evaluation about the radio interference (RI) level of ultra-high-voltage (UHV) AC power lines. To obtain this function, a large number of RI measurements in heavy rain condition were done using different conductor bundles in a corona cage. Then, the excitation function in heavy rain condition was obtained by least-square fitting these measured values. After that, the validity of this function was verified with the statistical data measured from the Hubei long-term station, which is located under the operating 1000 kV Jindongnan–Nanyang–Jingmen UHV AC transmission lines. It turns out that the deviation between the prediction and the long-term average value is 1.1 dB in heavy rain condition, and 1.3 dB in fair weather condition. In addition, the long-term data measured in Hubei Station show that the conversion laws of RI at different weather conditions in International Special Committee on Radio Interference (CISPR)18 are also applicable to 1000 kV UHV transmission lines.

Calculating the Surface Potential Gradient of Overhead Line Conductors

The surface potential gradient is a critical design parameter for planning overhead lines since it determines the level of corona loss, radio interference, and audible noise. The majority of existing surface gradient calculations are based on analytical methods which restrict their application in simulating complex surface geometry. This paper proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. With this method, stranding shape, protrusions, the proximity of tower, the type of tower, bundle spacing, and bundle arrangement can be taken into consideration when calculating surface potential gradients. A sensitivity study on the factors affecting surface gradient distribution is performed.

Prediction of Egyptian 500-kV Overhead Transmission Line’s Radio Interference by Using the Excitation Function

Abstract This article presents applications of the excitation function on the prediction of the radio interference (RI) of overhead transmission line (OHTL), due to corona effect. These applications are done under different weather conditions such as heavy rain, wet conductor, and fair weather.Also, this article investigates the factors influencing the RI level, namely, the height of conductors, phase spacing, number of subconductors in the bundle, diameter of subconductor, and subconductor spacing in the bundle.In this article, it is shown that the RI level is dependent on the weather conditions. Where the RI level under heavy rain has the maximum level, hence, it should be considered as a basic level of any OHTL.

The Murchison Widefield Array: The Square Kilometre Array Precursor at Low Radio Frequencies

AbstractThe Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80–300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3-km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper, the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.

Application of Excitation Function to the Prediction of RI Level Caused by Corona Discharge

Radio interference (RI), as an aftereffect of corona discharge, is an important research topic in the field of electromagnetic compatibility, where excitation function is applied broadly to the prediction of RI level. This paper presents the theory of excitation function method used in the RI level prediction. Then, some practical problems related to this method are discussed. The propagation procedure of corona current is solved by the phase-modal transformation, and the impedance matrix of multi transmission lines is calculated by a double logarithmic approximate model of Carson's Ground-Return impedance. At the same time, in order to calculate the RI level when total line corona is assumed, an analytical formula is deduced for integral operation. Based on the above solutions, an algorithm is presented and applied to the prediction of RI level of a practical overhead transmission line. Comparison of prediction and measurement results indicates that the algorithm proposed in this paper is effective and feasible.

Characterisation of electromagnetic properties in iron-mine production tunnels

Modern underground mines require reliable wireless communication for transmitting voice data, operating surveillance cameras, and monitoring mining equipment such as heavy vehicles. The electromagnetic characteristics of mines therefore have to be considered when determining the type of wireless technology for such critical applications. In this reported work, measurements of radio interference levels, path loss, and multipath propagation are performed in the world&apos;s now largest iron ore mine, situated in Sweden, to determine a suitable wireless technology for this mine.

Radio meteor detection in Malaysia

T Meteor is a luminous effect, light is created as the rocky body is frictionally heated to incandescence when entering Earth‟s atmosphere. The ionized trails of the meteor are also capable of reflecting radio signals from terrestrial stations, which include those broadcasted by commercial FM and TV stations. For this research, 3 sites are identified as candidates but only the best will ultimately be utilized to do the research. The selection criterion depends on the radio frequency interference (RFI) level and whether they have any free FM frequency from local radio stations. The 3 sites are Jelebu in Negeri Sembilan, Behrang in Perak and Merang in Terengganu. The best site is Behrang and the average floor noise level at this site within the FM frequencies of 88 MHz to 108 MHz is -97.111 dBm. The average number of meteor detections in the span of three days is 48 meteors per day. A number of 50 underdense and 38 overdense meteor trails are detected for the first day.

Interference mitigation in WSN by means of directional antennas and duty cycle control

ABSTRACTNetwork spanning algorithms, such as ZigBee‐native and Stojmenovič, constitute a crucial element in the wireless sensor network design, by determining its potential for reliability and fault‐tolerance. The interconnections between nodes have a great impact on the radio interference level present in such a network and may create a serious electromagnetic compatibility issue in some cases. It can be proved that the total interference incurred by a statistical node can be diminished in two ways: either by using directional antennas or by setting an upper limit on the duty cycle of each network node. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Electromagnetic interference and shielding of valve hall in HVDC converter station

The electromagnetic interference (EMI) from the valve hall as an important consideration in the design of high voltage direct current (HVDC) converter stations is analyzed by electromagnetic field numerical method and measurements. By using moment method, the EMI filed strength level as well as radio interference level (RIL) of the valve hall during the normal operation are computed after an antenna model is built for the valve tower. According to the character of EMI obtained, the practical shielding measures for valve hall are discussed to satisfy the relative standards. The test results for the ±500 kV converter station show that both the numerical method and shielding technique used in this paper are practical.

Surveying RFI for a new Brazilian Solar Spectroscope site

AbstractBrazilian Solar Spectroscope (BSS) carry out high time (0.01–0.1 s) resolution solar spectral investigations within the frequency range 1–2.5 GHz on a daily basis. At the moment, a new site is imposed to this facility. This site change became necessary due to both factors: the growing level of radio frequency interference (RFI) signals at actual site and requirements of rising up a new building at the BSS antenna location. We present results of RFI signals search at INPE-Cachoeira Paulista area as purpose to define a new BSS site.

Time varying interference statistical distribution for direct-to-user satellite applications

Adjacent co-channel satellite systems might lead to unacceptable mutual radio interference levels due to their close spacing in orbit and to the reduced antenna sizes at the user's reception. Tropospheric propagation impairments along with the interference effects are of utmost importance for the reliable design of modern satellite communication systems operating at Ku (14/12 GHz) and Ka(30/20 GHz) frequency bands and above. The objective of this Letter is the presentation of a novel analytical and accurate methodology for the prediction of the time varying carrier-to-interference ratio (CIR) statistical distribution under rain fading conditions. Appropriate physical space-time structure is employed for the correlation between the rain-induced attenuations on the two converging slant paths. The analysis proposed is flexible and incorporates various operational and geometrical parameters of the interference scenario. Numerical results illustrating the impact of those parameters on the space-time varying CIR statistics are presented and useful conclusions are drawn.

Computation of Radio Interference Levels in High Voltage Transmission Lines with Corona

In this article, an analysis of radio interference levels due to high voltage transmission lines with corona is presented. A method to predict radio interference levels, which based on Gary's method and modal decomposition theory, is described and presented, considering also the skin effect in conductors and in the ground plane. Several application examples for 3-phase lines are presented and the results are compared with measurements published elsewhere.

Using large radio telescopes at decametre wavelengths

With the aim of evaluating the actual possibilities of doing, from the ground, sensitive radio astronomy at decametre wavelengths (particularly below ∼ 50 MHz ), an extensive program of radio observations was carried out, in 1999–2002, by using digital spectral and waveform analysers (DSP) of new generation, connected to several of the largest, decametre radio telescopes in the world (i.e., the UTR-2 and URANs arrays in Ukraine, and the Nançay Decametre Array in France). We report and briefly discuss some new findings, dealing with decametre radiation from Jupiter and the Solar Corona: namely the discovery of new kinds of hyper fine structures in spectrograms of the active Sun, and a new characterisation of Jupiter's “millisecond” radiation, whose waveform samples, with time resolution down to 40 ns, and correlated measurements, by using far distant antennas (3000 km), have been obtained. In addition, scattering effects, caused by the terrestrial ionosphere and the interplanetary medium, could be disentangled through high time resolution and wide-band analyses of solar, planetary and strong galactic radio sources. Consequences for decametre wavelength imaging at high spatial resolution (VLBI) are outlined. Furthermore, in spite of the very unfavourable electromagnetic environment in this frequency range, a substantial increase in the quality of the observations was shown to be provided by using new generation spectrometers, based on sophisticated digital techniques. Indeed, the available, high dynamic range of such devices greatly decreases the effects of artificial and natural radio interference. We give several examples of successful signal detection in the case of much weaker radio sources than Solar System ones, down to the ∼ 1 Jy intensity level. In summary, we conclude that searching for sensitivity improvement at the decametre wavelength is scientifically quite justified, and is now technically feasible, in particular by building giant, phased antenna arrays of much larger collecting area (as in the LOFAR project). In this task, one must be careful of some specifics of this wavelength range—somewhat unusual in “classical” radio astronomy—i.e., very high level and density of radio interference (telecommunications) and the variable terrestrial ionosphere.

Pilotless timing recovery for baseband multicarrier modulation

This paper describes a multicarrier modulation timing recovery algorithm that does not require use of a designated pilot tone. Instead, all or some received subchannels are used to estimate phase and frequency errors. Algorithms for both acquisition and tracking are presented, and simulation results show excellent performance. The algorithm provides a useful timing recovery approach for environments in which use of a designated pilot is infeasible or undesirable, such as on digital subscriber lines corrupted by high levels of broadcast AM or amateur radio interference.

Removing Radio Interference from Contaminated Astronomical Spectra Using an Independent Reference Signal and Closure Relations

The growing level of radio frequency interference (RFI) is a recognized problem for research in radio astronomy. This paper describes an intuitive but powerful RFI cancellation technique that is suitable for radio spectroscopy where time-averages are recorded. An RFI signal, is constructed from the cross power spectrum of the signals from the two polarizations of a reference horn pointed at the source of the RFI signal. The RFI signal paths obey simple phase and amplitude closure relations, which allows computation of the RFI contamination in the astronomical data and the corrections to be applied to the astronomical spectra. Since the method is immune to the effects of multipath scattering in both the astronomy and reference signal channels, clean copies of the RFI signal are not required. The method could be generalized (1) to interferometer arrays, (2) to correct for scattered solar radiation that causes spectral standing waves in single-dish spectroscopy, and (3) to pulsar survey and timing applications where a digital correlator plays an important role in broadband pulse dedispersion. Future large radio telescopes, such as the proposed LOFAR and SKA arrays, will require a high degree of RFI suppression and could implement the technique proposed here with the benefit of faster electronics, greater digital precision and higher data rates.

Analytical Derivation of Maximum Tolerable In-Band Interference Levels for Aviation Applications of GNSS*

This paper presents an analytic derivation of the maximum levels of radio frequency interference (RFI) that can be tolerated for aviation applications of GNSS (global navigation satellite system). The derivation, which is included in the document of RTCA Special Committee-159 Working Group 6 on RFI to GNSS, includes consideration of many factors not addressed comprehensively in previous analyses. Such factors include quantization loss, intermediate frequency (IF) filtering losses, modulation imperfections in the navigation satellites (GPS, GLONASS, and Wide-Area Augmentation System [WAAS]), Doppler loop stress, processing gain losses due to realizable spreading codes, and oscillator phase noise. The goal of this paper is to demonstrate that the interference levels provided in RTCA's Minimum Operational Performance Standards (MOPS) are indeed close to the maximum levels that can be tolerated for aviation applications by moderate-cost modern digital receiver designs.

Radio interference and transient field from gas-insulated substations

Gas-insulated substations (GIS), owing to their compact nature, offer an attractive alternative to conventional substations in areas where space is limited such as in urban areas. Consequently, it is important to address the issue of environmental conditions within the substation and in the surrounding areas. This paper reports the results of radio interference (RI) and transient field measurements at two GIS in Ontario, Canada. For comparison with RI levels taken at the GIS, RI levels outside two hospitals in the Toronto area were also measured. The transient field study covers electromagnetic interference (EMI) levels generated during switching operations, and includes measurements inside and outside the GIS. Measurements show that RI levels from the GIS were either below background levels, or contributed little to the background. RI levels outside the GIS and the hospitals were similar. Peak transient field values up to 580 V/m were measured inside the station building, and dropped to background values of 10 V/m at about 120 m from the station. The transient field (E) dropped off at a rate of 3/2 power with distance (d) from the air-insulated 115 kV bus, i.e. E/spl prop/d/sup -1.5/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Meter Wave Interferometry

There are many outstanding astrophysical problems which are best studied at meter wavelengths. However this part of the spectrum has not been fully exploited for astronomical observations for several reasons. Firstly, the arrays at cm wavelengths provide higher resolution. Secondly, the level of man-made radio interference is very high at the longer wavelengths in industrialised countries, although it is not so high in countries such as India. Finally, the phase variations caused by the ionospheric irregularities are quite severe at meter waves, particularly for a large array (~ λ/35 rad.km-1).