Marine radar Type 12

Decca Radar; London

  • Year
  • 1951
  • Category
  • RADAR equipment
  • Radiomuseum.org ID
  • 303934

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 65
  • Main principle
  • ZF/IF 30,000 kHz
  • Wave bands
  • Wave Bands given in the notes.
  • Power type and voltage
  • Powered by external power supply or a main unit.
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: Marine radar Type 12 - Decca Radar; London
  • Notes
  • Decca Radar Ltd was founded in 1945 to produce marine radar systems. After extensive sea trials the first product, the Type 159B radar, was launched in 1950 and was an immediate success. The Type 12, which succeeded it in 1951, was designed with a higher specification and a 12" CRT PPI display instead of a 9" one.

    Modulator output to M503 magnetron 5.5 kV 6A pulses.
    Peak power output 7 kW.
    Frequency 9375 MHz ± 30 MHz.
    PRF 1 kHz.
    Pulse duration 0.1 or 0.2 µs.
    Scanner rotation speed 24 rpm ± 1 rpm.
    IF 30 MHz. Flat bandwidth from 25 to 35 MHz.
    Maximum gain from input to detector 86 dB.
    Max cable length from scanner to receiver unit 220 ft (67 m).
    Selectable ranges 1, 10 and 25 nautical miles.
    Calibration range rings and heading marker.
    Anti sea-clutter, anti rain-clutter, gain and tuning controls.
    Provision for an additional remote display unit.

    A delay switch prevents the application of EHT for 3 or 4 minutes after power up.

    Twin parabolic cheese antennas, each 3 in (7.62 cm) high by 4 ft (121.92 cm) wide, fed by double hoghorn assembly located at the focus.

    Horizontal beamwidth 1.7 deg, vertical beamwidth 23 deg. Near sidelobes (around 5 deg) at least 23 dB below the main beam; wide angle sidelobes (around 80 deg) 27 dB down.

    723A/B reflex klystron local oscillator, tunable over 9375 MHz ± 30 MHz. Output 25 mW, of which about 1 mW is transferred to the main waveguide via a two-hole directional coupler.

    CS3A crystal mixer. Current can be monitored at the display.

    A BTH BS52 gas TR switch was included in some models to protect the mixer crystal. When present, it is inserted in the receiving waveguide directly after the RF unit input flange.

    12TO1A CRT with mechanically driven deflection coils synchronised with the scanner. Magnetic focussing.

    An azimuth stabiliser driven by a ship's compass repeater can be connected between the bearing transmitter and receiver so that 0 deg on the PPI display indicates north, and the heading marker follows the ship's course.

    The system is powered by a Mackie Type 'S' 80 V 1000 Hz 500 VA alternator, driven by a 110 or 220 V compound wound DC motor with Creed governor, or by a 440 V 60 Hz 3-phase squirrel-cage induction motor. The scanner drive motors are also selected to correspond with the supply used.

    Valve complement:

    RF unit (10)
    M503 magnetron
    723A/B LO klystron
    BS52 TR switch
    2 EF91
    2 11E3
    EY91
    QS150/15
    QS95/10

    Receiver unit (27)
    10 EF91
    4 19G3
    3 UU5
    3 EF55
    2 6SN7
    2 EB91
    2 QS95/10
    ECC91

    Display unit (28)
    12TO1A CRT
    12 ECC91
    6 EB91
    3 EF91
    3 QS150/15
    EL38
    ECC91
    VR105/30

  • Author
  • Model page created by Bruce Taylor. See "Data change" for further contributors.

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