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Thread: BABS versus SBA system

  1. #1
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    Default BABS versus SBA system

    I would like to be sure with the identification of this navigation systems as I was not able to find out the full specification anywhere :

    Beam Approach Beacon System (BABS) - it was radio signal with continuous signal over the central line of runway, when incorrect direction the signal changed to dots on one side of runway and to dashes on the second one?
    Standard Beam Approach (SBA) - two radio beacons with acoustic/optical indication for pilot that he is above the beacon and at this moment he must have specific speed and altitude?

    Can anybody please confirm the definitions or correct them?

    TIA

    Pavel
    Czechoslovak Airmen in the RAF 1940-1945
    http://cz-raf.webnode.cz

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    Pavel, I think that the BABS was the ground based hardware you used when performing an SBA procedure.

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    Hi Pavel
    The 2 approach aids were meant to achieve the same objective i.e. guidance along a line but did so in slightly different ways. BABS was derived from the Rebecca/ Eureka Nav system where Eureka was a High frequency beacon and Rebecca was the recieving equipment in an aircraft using 2 sets of Yagi aerials , one either side of the a/c centreline to give bearing information. The combination was,I believe , used by resistance groups who were equipped with the Eureka to guide a/c to Drop Zones. For Approaches the beacon was put into a vehicle and positioned at one end of the runway with the a/c using the Rebecca equipment to decipher the signal.The SBA ,as I used it in 1961 at Ternhill, transmitted 2 lobes of radio energy that overlapped and interfered with each other. By careful control of the overlap a "beam" could be produced along a given line e.g. the runway centreline.The 2 lobes had different signals super-imposed, at Ternhill one lobe had Morse N-dash dot, and the other had Morse A -dot dash. Where they overlapped there was a continuous tone. The pilot heard this in his Headphones. I believe some a/c had a visual indication in the cockpit but at Ternhill there was only the aural signal. Range information was given separately by Marker beacons set along the centreline so by adjusting airspeed and rate of descent you could arrive over each marker at a height appropriate for the Glidepath usually 3 Deg's. The BABS Beacon was often referred to as a Radar Beacon and I believe gave direct range information, where the SBA System didn't.
    I am sure there will be others who can refine or correct a memory from nearly 50 years ago
    Regards
    Dick

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