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  •  scanners (12+ / 0-)

    if memory serves it was raining that day....satellite dish usually has less signal pick up during rain times my TV headphones picked up the audio protion of a video conference ( for one hour ) I checked google while it was going on .... and Jefferson Labs had posted a calendar for a performance review showing the scheduled video conference call they were talking about costs - benefits - results

    Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab also receives support from the City of Newport News and the Commonwealth of Virginia.

    The lab’s primary mission is to conduct basic research of the atom's nucleus using the lab’s unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). Jefferson Lab also conducts a variety of research using its Free-Electron Laser, which is based on the same electron-accelerating technology used in CEBAF.

    Managing and operating the lab for DOE is Jefferson Science Associates, LLC. JSA is a limited liability company created by Southeastern Universities Research Association and Computer Sciences Corp.

    https://www.jlab.org/...

    another audio pick up on TV headphones: several months before Jefferson National Lab when  Air Force One was parked at local Air Force base and he then drove to SF for fundraiser.... the radio frequency spectrum became available over TV headphones picked up CB conversation ( 32 miles from my location)  between two truck drivers making meet up plans for dinner at resturant that intersected their drive routes

    How Stuff Works - Radio Scanner

    http://electronics.howstuffworks.com/...

    http://electronics.howstuffworks.com/...

    http://www.antennahub.com/...

    http://www.bearcat1.com/...

    To tap into this ocean of electromagnetic dialogue and hear what all of these people are talking about, all you need is a scanner. A scanner is basically a radio receiver capable of receiving multiple signals. Generally, scanners pick up signals in the VHF to UHF range (see How the Radio Spectrum Works for details on these frequency bands).

    Scanner Basics
    Scanners typically operate in three modes:
    Scan
    Manual scan
    Search

    In scan mode, the receiver constantly changes frequencies in a set order looking for a frequency that has someone transmitting. Lights or panel-mounted displays show what channel or frequency is in use as the scanner stops on a given frequency. The frequencies can be preprogrammed on some models or manually set on practically all models.

    In manual scan mode, the user taps a button or turns a dial to manually step through preprogrammed frequencies one frequency at a time.

    In search mode, the receiver is set to search between two sets of frequencies within a given band. This mode is useful when a user does not know a frequency, but wants to know what frequencies are active in a given area. If the frequency the scanner stops at during a search is interesting, the user can store that frequency in the radio scanner and use it in scan mode.

    Some of the recently released scanners are capable of tracking municipalities and police frequencies in the 800-megahertz (MHz) range. This is known as trunk tracking of computer-controlled trunked radio networks.

    http://www.rollanet.org/...

    http://wcilscanner.home.comcast.net/...

    http://www.amazon.com/...

    Scanners and Secret Frequencies (Electronic Underground Series)  – September 1, 1993 by Henry L. Eisenson  (Author) , Bill Cheek

    Entertaining book describes the scanner world, the people in it, the equipment they use, and how they acquire and tune in to the "secret" frequencies.

    Hostage tactics are for those who can’t win their fights through elections, in Congress, in fights for the Presidency or in the Courts. It is a last gasp of those who cannot cope with the realities of our democracy. ~ Senator Elizabeth Warren

    by anyname on Wed Oct 02, 2013 at 09:15:42 PM PDT

    •  frogging (2+ / 0-)
      Recommended by:
      ek hornbeck, Man Oh Man

      Frequency frogging repeaters were commonplace in frequency-division multiplexing systems from the middle to late 20th century.

      http://en.wikipedia.org/...

      repeater

      http://en.wikipedia.org/...

      frequency frogging

      In telecommunication, the term frequency frogging has the following meanings:

      The interchanging of the frequencies of carrier channels to accomplish specific purposes, such as to prevent feedback and oscillation, to reduce crosstalk, and to correct for a high frequency response slope in the transmission line.

      In microwave radio relay systems, the alternate use of two frequencies at repeater sites to prevent feedback and oscillation.

      Note: Frequency frogging is accomplished by having modulators, which are integrated into specially designed repeaters, translate a low-frequency group to a high-frequency group, and vice versa.

      A channel will appear in the low group for one repeater section and will then be translated to the high group for the next section because of frequency frogging.

      This results in nearly constant attenuation with frequency over two successive repeater sections, and eliminates the need for large slope equalization and adjustments. Singing and crosstalk are minimized because the high-level output of a repeater is at a different frequency than the low-level input to other repeaters.

      It also diminishes group delay distortion. A repeater that receives on the high band from both direction and sends on the low band is called Hi-Lo; the other kind Lo-Hi.

      http://en.wikipedia.org/...

      Microwave radio relay is a technology for transmitting digital and analog signals, such as long-distance telephone calls, television programs, and computer data, between two locations on a line of sight radio path. In microwave radio relay, microwaves are transmitted between the two locations with directional antennas, forming a fixed radio connection between the two points. The requirement of a line of sight limits the distance between stations to 30 or 40 miles.

      Beginning in the 1950s and 1960s networks of microwave relay links, such as the AT&T Long Lines system in the U.S., carried long distance telephone calls and television programs between cities. These included long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the transcontinental traffic is now carried by cheaper optical fibers and communication satellites, but microwave relay remains important for shorter distances.

      http://en.wikipedia.org/...

      Microwave Radio Relay

      How microwave radio relay links are formed

      Because the radio waves travel in narrow beams confined to a line-of-sight path from one antenna to the other, they don't interfere with other microwave equipment, and nearby microwave links can use the same frequencies. Antennas used must be highly directional (High gain); these antennas are installed in elevated locations such as large radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay link installations are parabolic antennas, dielectric lens, and horn-reflector antennas, which have a diameter of up to 4 meters. Highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances.

      Over-horizon microwave radio relay

      In over-horizon, or tropospheric scatter, microwave radio relays, unlike a standard microwave radio relay link, the sending and receiving antennas do not use a line of sight transmission path. Instead, the stray signal transmission, known as "tropo - scatter" or simply "scatter," from the sent signal is picked up by the receiving station.

      Signal clarity obtained by this method depends on the weather and other factors, and as a result a high level of technical difficulty is involved in the creation of a reliable over horizon radio relay link. Over horizon radio relay links are therefore only used where standard radio relay links are unsuitable (for example, in providing a microwave link to an island).

      Though not commonly known, the US Military used both portable and fixed-station microwave communications in the European Theater during WWII.

      Starting in the late 1940s, this continued to some degree into the 1960s, when many of these links were supplanted with tropospheric scatter or satellite systems.

      When the NATO military arm was formed, much of this existing equipment was transferred to communications groups.

      The typical communications systems used by NATO during that time period consisted of the technologies which had been developed for use by the telephone carrier entities in host countries.

      One example from the USA is the RCA CW-20A 1–2 GHz microwave relay system which utilized flexible UHF cable rather than the rigid waveguide required by higher frequency systems, making it ideal for tactical applications.

      The typical microwave relay installation or portable van had two radio systems (plus backup) connecting two LOS sites.

      These radios would often provide communication for 24 telephone channels of frequency division multiplexed signal (i.e. Lenkurt 33C FDM), though any channel could be designated to carry up to 18 teletype communications instead. Similar systems from Germany and other member nations were also in use.

      Similar systems were soon built in many countries, until the 1980s when the technology lost its share of fixed operation to newer technologies such as fiber-optic cable and communication satellites, which offer lower cost per bit.

      Microwave spying

      During the Cold War, the US intelligence agencies, such as the National Security Agency (NSA), were reportedly able to intercept Soviet microwave traffic using satellites such as Rhyolite.

      Much of the beam of a microwave link passes the receiving antenna and radiates toward the horizon, into space. By positioning a geosynchronous satellite in the path of the beam, the microwave beam can be received.

      Hostage tactics are for those who can’t win their fights through elections, in Congress, in fights for the Presidency or in the Courts. It is a last gasp of those who cannot cope with the realities of our democracy. ~ Senator Elizabeth Warren

      by anyname on Thu Oct 03, 2013 at 01:47:49 AM PDT

      [ Parent ]

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