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Signal power measurements for a UK-based network of three beacon transmitters and five receiving stations operating on 5.290 MHz were taken over a 23 month period between May 2009 and March 2011, when solar flux levels were low. The median signal levels have been compared with monthly median signal level predictions generated using VOACAP (Voice of America Coverage Analysis Program) and ASAPS (Advanced Stand Alone Prediction System) HF prediction software with the emphasis on the near-vertical incidence sky wave (NVIS) links. Low RMS differences between measurements and predictions for September, October, November, and also March were observed. However, during the spring and summer months (∼April to August), greater RMS differences were observed that were not well predicted by VOACAP and ASAPS and are attributed to sporadic E and, possibly, deviative absorption influences. Similarly, the measurements showed greater attenuation than was predicted for December, January, and February, consistent with the anomalously high absorption associated with the "winter anomaly." The summer RMS differences were generally lower for VOACAP than for ASAPS. Conversely, those for ASAPS were lower during the winter for the NVIS links considered in this analysis at the recent low point of the solar cycle. It remains to be seen whether or not these trends in predicted and measured signal levels on 5.290 MHz continue to be observed through the complete solar cycle. Copyright 2012 by the American Geophysical Union.


This paper presents a comparison of Chilton ionosonde critical frequency measurements against vertical-incidence HF propagation predictions using ASAPS (Advanced Stand Alone Prediction System) and VOACAP (Voice of America Coverage Analysis Program). This analysis covers the time period from 1996 to 2010 (thereby covering solar cycle 23) and was carried out in the context of UK-centric near-vertical incidence skywave (NVIS) frequency predictions. Measured and predicted monthly median frequencies are compared, as are the upper and lower decile frequencies (10% and 90% respectively). The ASAPS basic MUF predictions generally agree with fxI (in lieu of fxF2) measurements, whereas those for VOACAP appear to be conservative for the Chilton ionosonde, particularly around solar maximum. Below ∼4 MHz during winter nights around solar minimum, both ASAPS and VOACAP MUF predictions tend towards foF2, which is contrary to their underlying theory and requires further investigation. While VOACAP has greater errors at solar maximum, those for ASAPS increase at low or negative T-index values. Finally, VOACAP errors might be large when T-SSN exceeds ∼15.


Walden M.C.,Plextek Ltd.
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) | Year: 2013

A lightweight, wideband tapered-slot antenna that uses an antipodal Vivaldi design and provides useable gain from ∼5 GHz to in excess of 50 GHz is described. Simulations and measurements are presented that show excellent agreement. This antenna design is currently deployed in handheld test equipment. © 2013 IEEE.


Walden M.C.,Plextek Ltd.
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) | Year: 2013

The design of a 16-element waveguide array employing radiating T-junctions that operates in the Ku band is described. Amplitude weighting results in low elevation sidelobe levels, while impedance matching provides a satisfactory VSWR, that are both achieved over a wide bandwidth (15.7-17.2 GHz). Simulation and measurement results, that agree very well, are presented. The design forms part of a 16 × 40 element waveguide array that achieves high gain and narrow beamwidths for use in an electronic-scanning radar system. © 2013 IEEE.


Patent
PLEXTEK Ltd | Date: 2010-03-19

In the sending of data in a network from a sending node to a receiving node via a relay node, the receiving node sends a notification arranged to notify both the sending node and receiving node of receipt of data at the receiving node. Notifications acknowledge that the data has been correctly received over each individual stage of transmission, and further acknowledge to the sending node that data has been correctly transmitted over the whole transmission path and received at the receiving node. The burden on the network of sending acknowledgments is reduced while notifications of data transmission over single stages and over the whole transmission path are provided.


Patent
Plextek Ltd | Date: 2010-05-19

Embodiments of the invention are concerned with frequency scanning antennas for transceiving radio frequency energy for use in detecting and monitoring ground-based targets. In one arrangement the frequency scanning antenna is embodied as a structure that is capable of emitting a radio frequency beam to a plurality of different angles about the antenna structure: the antenna structure comprises at least two travelling wave antennas, and the travelling wave antennas are disposed within the antenna structure such that the antenna structure is capable of emitting the beam at a first angle using one of said two travelling wave antennas and of emitting the beam at a second angle, different to said first angle, using the other of said two travelling wave antennas.


Patent
PLEXTEK Ltd | Date: 2010-06-04

A frequency scanning radar system includes a controller for controlling a frequency generator and a signal processor arranged to determine a Doppler frequency associated with a target. The frequency generator generates three or more sets of signals, each set of signals having a different characteristic frequency and including signals transmitted at a selected rate, and the radar controller selects the rate in substantially direct proportion to the characteristic frequency, whereby to normalize the Doppler frequency determined by the signal processor, such that the normalized Doppler frequency is substantially constant in relation to variation in the carrier frequency. In a frequency modulated radar system, each set of signals includes a sequence of modulation patterns, and the radar controller modifies a given modulation pattern in dependence on the characteristic frequency of the signal being modulated.


Patent
Plextek Ltd | Date: 2013-01-09

In sending data in a network from a sending node to a receiving node via a relay node, it is convenient to send notifications acknowledging that the data has been correctly received over each individual stage of transmission, and further to send notifications acknowledging to the sending node that data has been correctly transmitted over the whole transmission path and received at the receiving node. However, sending notifications acknowledging such receipt places a burden on the network. The present invention provides a relay node adapted receive a notification arranged to notify both the sending node and receiving node of receipt of data at the receiving node. This reduces the burden on the system, whilst allowing notification of data transmission over single stages and over the whole transmission path.


Trademark
PLEXTEK Ltd | Date: 2014-07-10

Electrical and electronic components; apparatus for recording, transmission or reproduction of sound or images; telecommunications components and apparatus; electrical and electronic equipment for transmitting and receiving signals; telematics equipment; security installations, apparatus and instruments; surveillance equipment; radar apparatus; radar apparatus for identifying and tracking targets, signal transmission or signal processing; radar apparatus for use in surveillance systems; radar apparatus for use in border, perimeter, area, pipeline and asset surveillance systems; image gathering apparatus; image processing apparatus; vehicle and personnel tracking systems; computers; computer software and hardware; communications software and hardware; computer software and hardware for use in position-fixing, target-tracking, target-identifying, signal transmission or signal processing, recordal, storage, transmission, retrieval, processing, analysis and display of data in graphical and/or other formats, metering, controlling and monitoring of lighting systems, and monitoring and controlling energy consumption; databases; electrical and electronic circuitry; cabling; power supply units; power amplifiers; cable connection devices; signal splitters; communications devices; network interface devices; radio equipment; transmitters, receivers and transceivers; wireless transmitters, receivers and transceivers; waveform generators; antennas image intensifiers; cameras; sensors; dimming modules; visual display units; metering hardware; parts and fittings for the aforesaid goods. Lighting apparatus; lighting systems; parts and fittings for the aforesaid goods. Market research and analysis services; marketing services; business planning services; business consultancy services; business advisory services; business strategy advisory services; arranging and conducting trade shows and exhibitions; business support services; database management services; data processing services; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Installation, repair and maintenance of computers, computer hardware, electrical and electronic equipment, radar apparatus, image gathering apparatus, telematics equipment, security equipment, surveillance equipment, radar apparatus, image processing apparatus, tracking systems, lighting apparatus and systems; diagnostic maintenance services; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Telecommunications services; rental of telecommunications apparatus and equipment; wireless communication services; data transmission services; telematics services; providing access to databases and computer networks; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Services for tracking, locating and monitoring of ground vehicles, nautical, maritime and avionic vessels for fleet management purposes; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Manufacturing services; information, consultancy and advisory services relating to the aforesaid services, also available online from a computer database or the Internet. Training and education services; arranging, planning, organising and conducting seminars; information services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Research, design and development services; design consultancy services; technology consultancy services; product testing services; design and development of computer software; hosting data on a database; technology audit services; quality audit services; technical project management services; technical planning services; advisory services relating to energy consumption and energy efficiency; advisory services relating to the environment and environmental impact; energy usage monitoring services; network planning services; installation, repair and maintenance of computer software; technical support services; computer diagnostics services; network diagnostics services; network equipment diagnostics services; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet. Services for tracking, locating and monitoring of assets and people; services for tracking, locating and monitoring of ground vehicles, nautical, maritime and avionic vessels for safety, security and insurance purposes; security services; surveillance services; legal advisory and support services; intellectual property advisory and support services; information, consultancy and advisory services relating to the aforesaid services, all of the aforesaid services also available online from a computer database or the Internet.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Innovation Voucher | Award Amount: 5.00K | Year: 2013

Plextek Consulting welcomes the award of a Cyber Innovation Voucher. This will help Plextek in its continuous improvement of protection of valuable intellectual property.

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