A Multiple-Channel Sub-Band Transient Detection System

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We have developed a unique multiple-channel sub-band transient detection system to record transient electromagnetic signals in carrier-dominated radio environments; the system has been used to make unique observations of weak, transient HF signals. The detection system has made these observations possible through improved sensitivity compared to conventional broadband transient detection systems; the sensitivity improvement is estimated to be at least 20 dB. The increase in sensitivity has been achieved through subdivision of the band of interest (an 18 MHz tunable bandwidth) into eight sub-band independent detection channels, each with a 400 kHz bandwidth and its own criteria. The system generates ... continued below

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Smith, David A. November 1, 1998.

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Description

We have developed a unique multiple-channel sub-band transient detection system to record transient electromagnetic signals in carrier-dominated radio environments; the system has been used to make unique observations of weak, transient HF signals. The detection system has made these observations possible through improved sensitivity compared to conventional broadband transient detection systems; the sensitivity improvement is estimated to be at least 20 dB. The increase in sensitivity has been achieved through subdivision of the band of interest (an 18 MHz tunable bandwidth) into eight sub-band independent detection channels, each with a 400 kHz bandwidth and its own criteria. The system generates a system trigger signal when a predetermined number of channels (typically five) trigger within a predetermined window of time (typically 100 ~s). Events are recorded with a broadband data acquisition system sampling at 50 or 100 Msample/s, so despite the fact that the detection system operates on portions of the signal confined to narrow bands, data acquisition is broadband. Between May and September of 1994, the system was used to detect and record over six thousand transient events in the frequency band from 3 to 30 MHz. Approximately 500 of the events have been characterized as paired bursts of radio noise with individual durations of 2 to 10 ps and separations between the bursts of 5 to 160 ps. The paired transients are typically 5 to 40 dB brighter than the background electromagnetic spectrum between carrier signals. We have termed these events SubIonospheric Pulse Pairs (SIPPS) and presently have no explanation as to their source. Our observations of SIPPS resemble observations of TransIonospheric Pulse Pairs (TIPPs) recorded by the Blackboard instrument on the ALEXIS satellite; the source of TIPP events is also unknown. Most of the recorded SIPP events do not exhibit frequency dispersion, implying propagation along a line-of-sight (groundwave) path; but seven of the pairs exhibit dispersion characteristic of skywave propagation via refraction from the ionosphere. The maximum line-of-sight observation range for radio propagation extends as far as 300 km for a source at an altitude of 5 km, and 520 km for a source at 15 km. Refraction from the ionosphere, however, may allow HF radiation to propagate around the globe. Information about the times and locations of sources, in conjunction with regional, weather maps and computer models of ionospheric propagation, suggest that some SIPP events originate in the vicinity of large-scale thunderstorm complexes.

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  • Other: DE00003059
  • Report No.: LA-13525-T
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/3059 | External Link
  • Office of Scientific & Technical Information Report Number: 3059
  • Archival Resource Key: ark:/67531/metadc685603

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  • November 1, 1998

Added to The UNT Digital Library

  • July 25, 2015, 2:20 a.m.

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  • May 6, 2016, 10:56 p.m.

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Smith, David A. A Multiple-Channel Sub-Band Transient Detection System, report, November 1, 1998; Los Alamos, New Mexico. (digital.library.unt.edu/ark:/67531/metadc685603/: accessed November 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.