• Year
  • 1948 ??
  • Category
  • Commercial Receiver (may include amateur bands)
  • Radiomuseum.org ID
  • 165670

 Technical Specifications

  • Main principle
  • Superhet, double/triple conversion
  • Wave bands
  • Short Wave (SW only)
  • Power type and voltage
  • Alternating Current supply (AC) / 220 Volt
  • Loudspeaker
  • - This model requires external speaker(s).
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: Single Sideband Receiver HR-21 - MIM, Marconi International
  • Shape
  • Rack
  • Notes
  • The Single Sideband Receiver Type HR.21, made by Marconi Wireless Telegraph Company Chelmsford, is a dual-channel superheterodyne receiver covering the frequency band from 3 to 27.5 Mc/s in four ranges. In addition to reception of single side band transmission, provision is made for the reception of either side band of a double sideband transmission. The receiver is designed for receiving point-to-point or broadcast transmissions carrying music, telephony, multi-channel voice frequency telegraphy (MCVF) or facsimile. A variable-frequency LC first oscillator having a high degree of frequency stability enables the receiver to be tuned to any desired frequency in the band; six crystal-controlled spot frequencies are also available. A double superheterodyne circuit is employed with intermediate frequencies of 2.6 Mc/s and 100 kc/s.

    Frequency band from 3 to 27.5 Mc/s in four ranges: Range 1 = 3 to 6 Mc/s; Range 2 = 6 to 10 Mc/s; Range 3 = 10 to 17 Mc/s and Range 4 = 17 to 27.5 Mc/s. The receiver is designed to accept signals from coaxial lines of 75 Ohm impedance. A variable first oscillator covers the frequency band in four ranges that correspond to the four signal frequency ranges. A crystal-controlled first oscillator provides six spot frequencies. In the AFC system employed in this receiver, a frequency error in the second intermediate frequency (100 kc/s) caused by a change in the received carrier frequency causes a motor to operate. The received carrier and a local carrier of reference frequency are passed to a mixer whose output at the difference (or error) frequency is used to drive a four-phase variable reluctance motor. The motor is coupled to the tuninggcapacitor of the second frequency-change oscillator and changes the oscillator frequency so as to reduce the error to zero. Channel filters having bandwidths of either of 3.5 kc/s or 6 kc/s are included in each sideband channel. NOTE: The desired bandwidth for each channel must be specified when ordering. A switch enables either local or reconditioned carrier to be supplied to the detector. Local carrier is obtained from the 100 kc/s crystal-controlled reference oscillator; reconditioned carrier is derived from the received carrier. All the instruments necessary for checking operation are incorporated in the equipment. These instruments iclude a volume indicator, a carrier or upper-sideband detector meter, a lower-sideband detector meter and meters for indicating the supplies voltages and the anode current of each valve. A monitoring amplifier feeding HR or LR headphones is provided for checking the output to line from each channel.
  • External source of data
  • Bernhard Pedrazzini
  • Author
  • Model page created by Ernst Erb. See "Data change" for further contributors.

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