1959 - History of Ericsson - History of Ericsson

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Fig. 8 X 2443 Sending frequency response curve Sound pressure at point of measurement 2 dynes/cm". 600-ohm termination Fig. 9 Receiving frequency response curve dynes/cm- Fig. 10 X 2445 Distortion during sending as function of sound pressure at microphone 106 In the few instances in which the maximum permissible length of line must be exceeded, the telephone can be connected to mains by means of a suitable hell transformer. The transformer should deliver 11-50 V, including variations in the primary voltage. As a practical means of checking whether the current supply is adequate, the line current can be measured with the loudspeaking telephone connected. If the current exceeds 13 mA, no mains connection is required. A lower current may occur in systems with feed voltage below 48 V. The current supply may be too low also on very long lines in a high voltage system and on certain PAX's and PABX's. In order to cover all applications with a single type of telephone, the present model has been supplied with a switch underneath the instrument, having four positions, namely: 1. Delivery position The switch is in this position on delivery 2. Position for line currents above 25 mA 3. Position for line currents between 13 and 25 mA 4. Mains connection position. During receiving the instrument may temporarily consume up to 50 mA and must therefore be supplied with a device to maintain the working voltage constant. This consists of a nickel-cadmium accumulator which, during conversation, is charged from the line during idle periods and during sending, but supplies sufficient additional energy during the current peaks in the receiving periods. This built-in accumulator makes it possible to use the telephone on longer lines and with lower distortion than would be possible with any other kind of voltage stabilizer. The working characteristics of the accumulator have been found excellent. Even after total discharge, it quickly becomes recharged during conversation to a voltage adequate for use of the telephone. The subscriber is therefore never let down by an occurrence of this kind. The principles and solutions employed in the design of the Ericovox have meant that its transmission characteristics fulfil extremely high demands. Its performance will be seen from fig. 8-12. Fig. 8 shows the frequency response curve during sending. As is seen, the curve has the ideal shape required to compensate the higher line attenuation at high frequencies on long lines. The sending gain has been made about 20 db higher than for an ordinary modern type of telephone, in order to compensate for the usually about 10 times greater distance between the microphone and the speaker's mouth. In subjective volume tests the efficiency when speaking at 50 cm from the instrument has been found to be + 10 db relative to ARAEN.* This value may be said to correspond to a sending reference * 1. CCITT Livre Vert, Tome IV. 2. Ericsson Technics No. 1, 1953; F Markman: Assessment of Transmission Properties of Telephone Instruments Based on Articulation Tests.
Fig. 11 X8158 Distortion during receiving as function of line e.m.f. (impedance 600 Q.) a with extra amplification, i.e. with lony-linc button depressed b with normal amplification Fig. 12 x 8166 Instrument impedance (Z) within 300—3400 cycle band Instrument impedance Z = R 4- jX equivalent relative to SFERT of + 7 db. Studies of the speech volume measured across the line terminals have shown that a loudspcaking telephone with this sending efficiency delivers virtually the same speech voltages to the line as those obtained from a modern telephone with corresponding line attenuations. This implies that sending will always be satisfactory under the conditions given in table 1. If the transmission performance for a certain connexion is poor, it will be noticed first by the user of the loudspeaking telephone. He notices it in his own reception and can take the necessary action. From the transmission point of view, therefore, a subscriber conversing with an Ericovox user is directly benefited by the loud speaking facility. The response curve during receiving is shown in fig. 9. This curve holds good from the horizontal plane up to an angle of 45°. It is essentially flat. The receiving efficiency can be regulated to an agreeable level by the subscriber within wide limits by means of the long-line button and the volume control. Fig. 10 shows the distortion during sending as function of sound pressure. It should be noticed that the sound pressure at the microphone will in normal cases not exceed 1-2 dynes/cm- compared with 5-10 dynes/cm- for normal handsets. The speaking distance with loudspeaking telephones is normally not less than 40-50 cm. Fig. 11 shows the distortion during reception as function of line e.m.f. The instrument impedance (Z) is shown within the 300-3400 c/s band in fig. 12. The impedance has been set to 600 ohms (± 10 %) and phase angle 0° (± 15°). This impedance can be easily changed if necessitated by future requirements. 107
Page 1: 4 1959
Page 4 and 5: Ericovox, the One-Piece Loudspeakin
Page 6 and 7: Fig. 3 X 8156 Block schematic of co
Page 8 and 9: Fig. 5 x 8163 The Ericovox, L M Eri
Page 12 and 13: 108 The Ericovox meets the requirem
Page 14 and 15: Fig. 3 Grouping of components in wi
Page 16 and 17: Fig. 9 X 8132 Case with pyramid-sha
Page 18 and 19: Fig. 12 X8134 Instrument with base
Page 20 and 21: Fig. 18 X8135 The locations of the
Page 22 and 23: Gothenburg Automatic Transit Exchan
Page 24 and 25: Fig. 3 x 8181 Block schematic of gr
Page 26 and 27: Fig. 6 122 x 8180 Block schematic o
Page 28 and 29: Fig. 8 X 2472 Link circuits for ori
Page 30 and 31: Fig. 10 X8182 Traffic supervisor's
Page 32 and 33: Fig. 2 X8167 Relay switchboard AMD
Page 34 and 35: 130 Priority The switchboard is des
Page 36 and 37: Crossbar Exchange Installed on Larg
Page 38 and 39: L M Ericsson to Undertake First C.T
Page 40: The Ericsson Group Associated and c

1959 - History of Ericsson - History of Ericsson

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