13 thoughts on “Brazilian Navy’s beacon antenna

  1. Ancient Alien

    No, no, you’re all wrong. It’s a giant spider web built by huge, hairy spiders that were irradiated by atomic bomb tests in the Amazon jungle in the 1950s!

    Reply
  2. Mike N7MSD

    Yeah, it’s an umbrella, which in turn is a very elaborate (and usually HEAVY) capacitance hat. They must get a lot of wind there and / or be running a lot of power to go that route instead of making the vertical element (the tower AKA “stick” in AM / MW broadcast parlance) taller.

    Most lower-power NDB’s use the much simpler Marconi-T which is the Umbrella’s predecessor & works the same other than less capacitive reactance: https://en.wikipedia.org/wiki/T-antenna

    The Umbrella was invented later. For the “new” ham radio bands 630m / 475 KHz and 2,200m / 137 KHz, most hams use T’s as a ladder-line fed horizontal 160m dipole can be easily repurposed into a T-vertical by tying the ladder line wires together at the radio / tuner: here the feed line becomes the vertical radiating element and the dipole legs become the T cap hat. Richer hams can afford to go the full umbrella route.

    Finally, this picture reminded me of DX Engineering’s Thunderbolt 160m vertical:

    https://www.dxengineering.com/parts/dxe-160va-1

    Smaller due to higher freq band but electrically identical.

    Reply
  3. Alexander, DL4NO

    From what I see, the wires create an electrically “thick” monopole antenna: If you look carefully, you see wires from the top, to a support line and back to the bottom of the mast. For a capacitor hat you would try to put the wires on top as far away from the mast as possible.

    For further investigations, you would need some idea of the operating frequencies. A marine beacon would change its frequency according to the shortwave conditions, therefore the need for a “thick” antenna. This is even more valid if the beacon hops over several bands as the stations of the International Beacon Project do. See https://www.ncdxf.org

    The International Beacons Project uses standard multi-band ham radio antennas that often rely on harmonic frequencies. You could not do this for the marine bands.

    Reply
  4. Mangosman

    For current operating VLF communications transmitters for underwater submarines https://www.raytheon.com/au/capabilities/mission-systems
    https://www.navy-radio.com/xmtrs/vlf/holt-ant-01.JPG this aerial can be folded down of cyclones (Hurricanes)
    https://en.wikipedia.org/wiki/Naval_Communication_Station_Harold_E._Holt
    http://www.navy-radio.com/commsta/holt.htm
    Harold E Holt was an Australian Prime Minister who was drowned off a Cheviot Beach Victoria.

    Reply
  5. Steve K9NUD

    Because all the guy wires use insulators, the tower itself is isolated from the ground and acts as a driven element. The complex web is probably a combination of capacitance hat and additional guying.

    Reply
    1. Steve K9NUD

      Gosh, I should have searched too. Turns out I was right! I was also thinking LF or VLF. The Brazilian Navy has a fleet of subs, so this would make perfect sense.

      Reply
      1. Julio Cesar Pereira

        Unfortunately, these NDBs have been decomissioned and few remain today. I live not very far from this NDB. It transmits on 300kHz.

        Reply

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