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HF Radio Systems and Techniques, 2003. Ninth International Conference on (Conf. Publ. No. 493)

Date 23-26 June 2003

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Displaying Results 1 - 25 of 55
  • A simple polarisation fading model for HF propagation in the ionosphere

    Publication Year: 2003 , Page(s): 131 - 135
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (403 KB)  

    A method of ray tracing to investigate the effects of Faraday rotation in the ionosphere is presented in the current paper. By applying analytical ray tracing, a polarisation fading model is developed for the HF signal propagating in a simple ionosphere. The scale of the ionospheric inhomogeneities being considered is large compared to the wavelength of the signal so that GO approximation remains applicable. Details on development of the model, results of the calculation and the effects of Faraday rotation on the signal are presented in subsequent sections. A comparison between the results ascertained from the simple model and a full 3D ray tracing package is included to verify the validity of the model. View full abstract»

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  • The role of HF navigation systems performance in selected aviation accidents

    Publication Year: 2003 , Page(s): 262 - 264
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    Most aviation accidents are caused by human errors and in poor weather; the effect of technical faults appearing either in the aircraft or ground systems has been negligible. Typically the pilot has ignored or misinterpreted the minimum altitude defined by authorities or performed otherwise hazardous flight operations. Sometimes, however, investigations have revealed, as a by-product, inadequate navigation equipment performance in conjunction with such disasters. The paper discusses previously unpublished examples in which the radiation characteristics of HF navigation beacons have been found unacceptable. Coupling of radiated energy from the beacon antenna to a too close overhead line can cause phantom guidance - often along this power line - when observed by an aircraft ADF receiver. Excessive vegetation when covered by snow may deteriorate the impedance matching whereby the field strength drops even by 10-15 dB. Unwanted frequency modulation close to the carrier, e.g. from the power supply transformer can severely disturb commercial phase locked receivers. Therefore, flight tests do not necessarily reveal false directional guidance caused, e.g., by coupling effects. We emphasize, however, that in none of the cases discussed has there been any evidence related to navigation systems as a cause of accidents. View full abstract»

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  • Amateur radio at 30 MHz and below

    Publication Year: 2003 , Page(s): 171 - 175
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (463 KB)  

    Uses the GICCA categorisation model, which was developed by Carkhuff and Berenson (2002) to analyse the maturity of products and services. Highlights and explains some of the innovations in the hobby and to provide a framework for looking to the future. View full abstract»

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  • IP over HF as a bearer service for NATO formal messages

    Publication Year: 2003 , Page(s): 19 - 24
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    The aim of our study is to explore the use of STANAG 4406 Annex E on top of an HF radio subnet that offers an IP transfer service (STANAG 5066 and 4538). We have studied the interactions between protocols defined in STANAG's 4406 and in 4538, how they can interact in an optimum way with each other, and what the current limitations are. Protocols are described, and typical response times are measured in the lab on a perfect HF channel (no channel errors). Considerations regarding interoperability when running IP over HF are also given. View full abstract»

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  • Interactive digital voice over HF

    Publication Year: 2003 , Page(s): 31 - 36
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    The main objective of the present design has been the development of a HF band communication system providing digital voice transmission within around 3 kHz bandwidth, through ionospheric reflection, mainly, but not only, for aeronautical environment. Interactivity, as a basic design constraint, has shown that standard structures using single carrier modulations are not suitable at all because their reliability is mainly based on the use of powerful channel coding schemes and very long interleavers with delays of several seconds. On the other hand, OFDM (orthogonal frequency division multiplex) systems are more robust techniques facing the multipath effect as the main distorting source of this propagation mechanism. The combination of this characteristic with spread spectrum CDMA (code division multiple access)-like schemes provides an extreme robust modem without the need of powerful codes neither long interleavers to guarantee an specific data rate and quality of service. Therefore, we are able to design a high data rate system with the possibility of providing interactive digital communication. View full abstract»

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  • Trellis-ARQ error control for efficient Internet access over long haul rural radio links

    Publication Year: 2003 , Page(s): 136 - 139
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    Access to the Internet is considered essential and critically important to sustainability of rural economics and social development. Most rural communication centres, such as community telecentres (CTC) urgently need an error free long-haul digital radio link connection. Provision of an affordable and reliable narrowband radio link becomes essential to help them with their economic issues. The HF radio band freely available is, however, the most unreliable medium for data transmission. We, therefore, propose use of a new metric-activated error detecting trellis coded modulation (EDTCM) system coupled with an ARQ for extending the Internet access capability of these links considerably. View full abstract»

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  • The simulation of HF off-great circle propagation effects due to large scale electron density structures within the polar cap and due to the mid-latitude trough

    Publication Year: 2003 , Page(s): 250 - 255
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. Whilst experimental work has produced many useful results (Warrington, E.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.144, p.241-9, 1997; Rogers, N.C. et al., IEE Proc. on Microwaves, Antennas and Propag., 2003; vol.144, p.91-6, 1997), they were obtained for a small number of paths and frequencies. In order to be able to develop tools to enable such effects to be considered in the design and operation of HF radio systems for which the signals impinge on the polar cap ionosphere, but for frequencies and paths not subject to experimental investigation, a ray tracing model has been developed. The results obtained from the ray tracing simulations are presented together with examples of experimental observations. However, it is well known that the high latitude ionosphere is an extremely complex HF propagation environment and, therefore, precise agreement between experiment and simulation has not been attempted and should not be expected. View full abstract»

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  • An efficient means of implementing spatial filtering of HF signals propagated over high latitude HF communication paths for the purposes of improving data throughput

    Publication Year: 2003 , Page(s): 271 - 277
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    The high latitude ionosphere is a dynamic region that is subject to a variety of disturbed conditions, which affect the propagation of HF radio signals. Point-to-point digital communication systems at high latitudes attempting to utilise the narrowband HF ionospheric radio channel can suffer severe performance degradation when the time or Doppler dispersion exceeds certain, system dependent, bounds. The presented results are based around measurements of narrowband pulse compression channel sounding signals, made using a six channel spaced array receiving system, over two high latitude paths. Super resolution direction finding studies of this data revealed significant directional effects in the received signals. Of particular note is an often observed directional structure to received Doppler spread signals. These investigations indicate that spatial filtering, using simple arrays of antennas, can significantly reduce the level of Doppler spread presented at the inputs to modern high speed digital modems. The use of fast solver methods to find the best spatial filtering solutions results in very similar performance at reducing Doppler spread and massively reduced calculation times, thus raising the possibility of implementation of spatial filtering in a real system. View full abstract»

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  • BOWMAN HF IP network solution

    Publication Year: 2003 , Page(s): 25 - 30
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The BOWMAN HF networking solution is based on easing the integration of the RF-5800H radio into the BOWMAN network using a concept called bridging. This has greatly simplified the IP management problem associated with the HF subsystem. The HF Networking scheme utilizes the STANAG 4538 capabilities in association with performance enhancing technologies such as concatenation and compression to achieve the required system throughputs. The HCMAC protocol has been developed to provide roughly twice the capacity achievable using STANAG 4538 FLSU (for equal latency) in ground wave and NVIS HF scenarios where the reduced robustness of the HCMAC signaling can be tolerated. View full abstract»

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  • Variations in direction of arrival of HF signals propagating over a high latitude path under quiet and disturbed geomagnetic conditions

    Publication Year: 2003 , Page(s): 165 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    A new network of transmitters and receivers has been installed in northern Scandinavia (including Svalbard), capable of measuring the time delay and Doppler spread characteristics and the directional structure of received signals on three HF paths. Based on the large amount of data expected from this experiment, a statistical classification of signal directional characteristics under various geophysical conditions and for all seasons can be made. In this paper, cases of both quiet and disturbed geomagnetic conditions have been studied, and comparisons have been made with data from magnetic disturbance observatories in the same geographic region. View full abstract»

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  • A phase shift technique for intermodulation cancellation

    Publication Year: 2003 , Page(s): 75 - 77
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (269 KB)  

    In a multi-carrier transmission system, intermodulation distortion (IMD) is generated because of amplifier non-linearities. The presence of IMD degrades the performance of such systems. In this paper, an IMD cancellation technique based on phase shift is presented. The technique depends on applying pre-determined phase shifts to each carrier signal before they are combined. Then, an increased number of amplifiers are used to enable the cancellation of chosen IMD components. The amount of phase shift depends on the frequency components to be cancelled. Simulation results are presented to show the effectiveness of the technique proposed. View full abstract»

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  • HF data link protocol enhancements based on STANAG 4538 and STANAG 4539, providing greater than 10 kbps throughput over 3 kHz channels

    Publication Year: 2003 , Page(s): 64 - 68
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    STANAG 4538 defines a third generation (3G) HF system that includes a synchronous Automatic Link Establishment (ALE) system coupled with efficient data link protocols. The data link protocols, collectively known as XDL, have been integrated into the Harris RF-5800H HF man-pack radio system and are included in the Harris radio being produced for the UK BOWMAN program. This paper begins with an overview of the existing XDL data link protocols defined in STANAG 4538. Next, an overview of HDL+ is presented. It is not the goal of this paper to be an overall definition of the protocol but to discuss the major enhancements relative to the XDL protocols. Next, the paper presents some simulated performance results of HDL+ over the nonfading additive white Gaussian noise channel and the fading poor channel. Data are presented for message payloads of 5,000 and 50,000 bytes. Performance are contrasted with that of standard HDL. The paper concludes with a summary and a short discussion of future areas of investigation. View full abstract»

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  • Iterative decoder-aided equalization of STANAG 4539 high data rate waveforms

    Publication Year: 2003 , Page(s): 42 - 47
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The area of digital communications has undergone a significant transformation in the last ten years due largely to the discovery of turbo codes. The "turbo" concept can be applied to more than just forward error-correction (FEC) schemes. For example, waveforms developed for the high frequency (HF) band typically place an interleaver between the FEC scheme and the transmitted symbols. The purpose of this interleaver is to decorrelate the errors caused by slow fading multipath channels encountered on HF. If no interleaver were used, most FEC schemes would become ineffective (e.g. convolutional codes). The "turbo" concept can be applied to HF waveforms which employ an interleaver by iteratively exchanging soft information between the equalizer and the FEC decoder. This paper investigates the possible performance improvements of applying this technique to a family of high data rate HF waveforms defined in NATO STANAG 4539. Different data rates and interleaver sizes are simulated on a variety of channels to determine the benefits. Instead of standard bit error rate performance curves, block error rate curves are provided since most modern day applications send groups of bits (packets) and expect each group to be received error free. Following this, latency and computational complexity are discussed to assess the feasibility and benefits of applying this technique to improve on-air performance of HF systems. View full abstract»

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  • A ground penetrating radar for Mars exploration, the GPR experiment on Netlander

    Publication Year: 2003 , Page(s): 282 - 287
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (453 KB)  

    Several missions are planned which should deposit on Mars a number of landers that will perform detailed observations of the planet's surface, subsurface and atmosphere. The CNES Netlander mission aims at establishing a network of 4 geophysical stations. They will offer a unique opportunity to explore the interior of Mars, its subsurface, atmosphere and ionosphere from 4 landing sites representing different geophysical conditions. One of the most important objectives is the investigation of the underground geological entities and the search for water reservoirs in the form of ground ice or even liquid water. The GPR experiment on Netlander, Berthelier et al. (2000), Ney et al. (2002), Ciarletti et al. is a ground penetrating radar that has been proposed to perform such observations. It is based on a new concept that will allow to explore the subsurface from a fixed position with the goal of achieving a 3D imaging of the underground. Features of instrumentation are discussed. View full abstract»

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  • Multi-channel equalisation and interference cancellation for HF STANAG 4285 transmissions

    Publication Year: 2003 , Page(s): 265 - 270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (473 KB)  

    Adaptive multi-channel equalisation is investigated for HF STANAG 4285 transmissions by processing data collected during March-April 2000. The demodulation performance of a conventional multi-channel receiver is compared to that of a bespoke multiple steered-beam method, in interference scenarios in which a single-channel receiver could not acquire, or had difficulty in acquiring, a signal. It is shown that the multiple beam architecture can adapt using a short training sequence whilst maintaining excellent demodulation performance. Multi-channel processing for HF STANAG 4285 is shown to provide a reduction in probability of bit error of two orders of magnitude or more over a COTS modem. View full abstract»

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  • The choice of operating frequency in HF surface wave radar design

    Publication Year: 2003 , Page(s): 278 - 281
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    Radars operating in the HF band (3-30 MHz) are primarily of interest because of their ability to provide an over-the-horizon (OTH) surveillance capability. There are two types of such OTH radars - skywave (typically capable of detecting. targets at ranges of thousands of kilometres) and surface wave (typical detection ranges of hundreds of kilometres). Skywave radars, which are generally large, complex and expensive, rely on the ionosphere to refract signals beyond the horizon. The dynamic nature of the ionosphere places considerable demands on the radar, one of them being a very wide operating bandwidth (e.g., several octaves). Surface wave radars, on the other hand, are generally less expensive and complex, and can operate robustly over a somewhat narrower band, easing the constraints on RF and antenna design. This leaves the radar designer with an interesting choice with regards to the system operating frequency and bandwidth. The paper discusses the various factors that influence that choice and highlights some of the difficulties of selection. View full abstract»

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  • Improved bandwidth and efficiency of short antennas by the use of radials

    Publication Year: 2003 , Page(s): 210 - 215
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    Design equations are given for the radius of a disc radial, in terms of the antenna diameter and antenna length, and it is shown how the size of spoked radials is simply related to this disc radius. Radials increase the radiation resistance of a short antenna and can resonate it at the frequency of interest. These two improvements together considerably increase the efficiency of the antenna system by reducing the losses in the matching circuits. Further increases in input resistance may be possible by feeding the antenna within one of its radial spokes. The bandwidth is considerably increased over that of the same antenna without radials, and for short antennas is proportional to the radius of the radial. However, the bandwidth is always less than that of a half wave dipole of the same antenna diameter. The radiation pattern of a short antenna is essentially the same as a half wave dipole no matter how short it is, and this is unaffected by the addition of radials. View full abstract»

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  • Authors List

    Publication Year: 2003 , Page(s): xi - xii
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (183 KB)  

    First Page of the Article
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  • High data rate VHF/UHF file transfer by a software defined multi-band radio

    Publication Year: 2003 , Page(s): 185 - 189
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    Germany and France have set up a joint program called Multiband Multirole Radio (MMR) to investigate a next generation tactical radio communication system focusing amongst others on being programmable and providing extended capacity. As one part of this program EADS RACOMS undertook the task to design a non-hopping VHF/UHF waveform for high data rate file transfer (HDRFT) over TCP/IP operating between 30 and 600 MHz. Target data rates are 32 and 64 kbit/s to be achieved in 25 kHz typical VHF bandwidth. Message structure needs to be flexible to adapt to actual packet size, limited by the maximum transfer unit (MTU) which defines the maximum allowed TCP/IP packet size. The overall frequency band of the MMR is defined from 2 to 600 MHz, thus requiring a multi-band front-end. Due to software defined applications different transmission bandwidths have to be handled. To keep HW constraints low, the analogue-digital border should be assigned to the highest possible IF. Analogue to digital converters (ADC) are key elements in such hardware architecture. The paper presents the HDRFT waveform approach including an extraordinary 3-PSK modulation scheme and simulation results depicting the performance potential. The content of the MMR program is briefly illustrated. The programmable multiband HW architecture is introduced. View full abstract»

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  • Measurements of the radiation and loss resistances of small HF multi-turn multi-resonant tuned loops

    Publication Year: 2003 , Page(s): 57 - 63
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    We use our 'wideband-Q' method of finding and measuring the various resistance components of a small tuned loop (Underhill and Harper, IEE Electronics Letters, vol.38, no.18, p.1006-8) to measure and assess a variety of small HF tuned loops. The method relies on bandwidth, and hence Q, measurements being made over the two to three octave tuning range of such tuned loop antennas. Because the measured loop inductance remains constant, until the self resonance of the loop is approached, the Q values also deliver the total combined loss and radiation resistance as measured at the antenna terminals. We find from theory, and confirm by measurement, that the several radiation modes of a loop and the identifiable loss mechanisms in general vary with different powers of the frequency. Where two components vary with the same power of frequency, we can separate these by varying the loop or loop conductor sizes, or the placement and orientation of the loop in the environment, and then by applying simple multi-factor analysis to the measurements. The results are found to be highly repeatable and have error limits of a few percent only. We also observe that the dipole radiation mode is much reduced for the multi turn loop, typically to the point of insignificance, particularly when the loop is well balanced (Underhill and Blewett, M.J., 1997). View full abstract»

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  • On-air test and evaluation of STANAGlong-range beyond line of sight 4538

    Publication Year: 2003 , Page(s): 13 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (481 KB)  

    The benefits of using high frequency (HF) circuits for both long-range beyond line of sight (BLOS) and short-range near vertical incidence skywave (NVIS) military applications are well documented. STANAG 4538 specifies an automated HF system that incorporates robust waveforms and protocols with the aim of providing faster link establishment and higher message throughputs under a variety of channel conditions. Under the auspices of the. NATO BLOS Communication WG, international trials have evaluated the link establishment and data link performance of S4538. Comparisons have been made with existing technologies such as MS-ALE and FS-1052. The testing has shown that S4538 offers a considerable improvement over MS-ALE in terms of increasing communications availability and decreasing LSU times. S4538 was also shown to be more reliable under poor channel conditions, such as those prevalent in the tactical environment. The operation of both point-to-point (PTP) and point-to-multipoint (PTM) protocols have been observed. Furthermore, the benefits of using RTCE information from sounding (or previous successful communications) has been observed. View full abstract»

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  • A study of reconfigurable analogue for DRM and HF systems

    Publication Year: 2003 , Page(s): 91 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    This paper focuses on the use of reconfigurable analogue technology to support multi-standard Digital Radio Mondiale (DRM) and high frequency (HF) communication systems. The choice of receiver architecture is discussed within the context of frequency adaptive systems and the low-IF receiver is introduced as an alternative to the zero-IF digital receiver. This paper also investigates the ability of field programmable analogue arrays (FPAAs) to implement matched filters within a low-IF receiver, thus providing the flexibility to support multistandard operation. View full abstract»

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  • Data transmission over HF radio channels using complementary sequences sets

    Publication Year: 2003 , Page(s): 244 - 249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    The paper describes an investigation of the system performances of a wide range of adaptive modem architectures based upon uncorrelated sets of complementary sequences (CSs). The aim of the study is to develop an optimum system configuration for the high frequency (HF) mobile radio channel with emphasis being laid upon robust data transmission. M-ary phase shift keying (MPSK) is the modulation scheme employed, although other modulation types are also appropriate. CS sets are shown to be an efficient means of designing modems by. putting their correlation properties to good use. It is concluded that, at baseband, uniform quantisation results in a degradation in the performance of the modem as expected. However at bandpass, an improvement in the performance of the modem at the expense of higher Eb/N0 values is observed when quantising. Under non-Gaussian and Rayleigh fading conditions, which are more realistic models for the severe conditions on the HF channel, considerable system performance is achieved by using CS sets with larger dimensions (i.e. increased sequence length and/or number of sequences per set). Such a benefit is obtained at the expense of increased redundancy. HF was chosen as a convenient and challenging demonstrator medium; however, in principle, the techniques can be applied readily to other frequency bands. View full abstract»

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  • Frequency-agile class-D power amplifier

    Publication Year: 2003 , Page(s): 81 - 85
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (329 KB)  

    The electronically tuned class-D power amplifier (PA) addresses the simultaneous needs for efficiency and frequency agility. The PA is based upon broadband transformer-coupled topology and uses a MOSFET operating in class D to deliver the maximum output power for given ratings. The output filter is a T network that provides a high impedance to and attenuation of the harmonics. The components of the output filter are bias-tuned inductors of a proprietary design and a voltage-variable capacitor implemented from a bank of high-voltage MOSFETs. The use of electronically tuned components allows the PA to be tuned and operated efficiently over a wide range of frequencies without band-switching. View full abstract»

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  • Coverage analysis for modern HF communication networks

    Publication Year: 2003 , Page(s): 125 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (438 KB)  

    High frequency (HF) coverage planning tools have been used successfully for many years to assist radio planners in designing HF networks and operating HF services. This paper describes techniques which have been derived as an adjunct to existing planning tools to improve their utility for use with modern HF systems and networks. The techniques factor in real-time frequency diversity and site diversity, which have a significant impact on the success rate for communication links. View full abstract»

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