Ericsson DIALOG - Page 18

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Fig. 26
The trans-
mitter cup
with hand-
set cord
and the two
conductors
to the
receiver
3.7.1 Transmitter
The external shape of the transmitter can be seen in fig. 27. The
transmitter design is such that the transmitter characteristics are
practically independent of the speaking position. The ratio (1,3:1)
between the highest and lowest transmitter resistance provides
good evidence of this when the transmitter. with constant feeding
voltage. is made to assume all possible positions.
The entire surface of the electrodes ( 6), (14) is in permanent
contact with the carbone granules (3). Consequentl y, the whole
electrical current will be conducted through the quantit y of carbon
affected by speech vibrations.
The stability is further improved by the rough walls of the granule
chamber. which prevent the carbon granules from packin g during
conversation. The electrode surfaces are gold plated to achieve
the best possible contact between them and the carb on g ranules .
Fig. 2 7
The trans-
mitt er
At high frequencies the transmitter response curve shows an
increased degree of sensitivity. This is achieved by the small
mass and frequency dependant stiffness of the diaphra gm system
(15). This stiffness is also a function of the loading on the
acoustical volume. The total acoustical volume consists of two
chambers separated by the transmitter inset frame. Thus the
transmitter cup forms the second chamber. This frame (11) has
three holes covered with fabric discs (12), (13) which at low
frequencies have virtually negligable acoustical impedance so
that the conical diaphragm is loaded by the total air volume in
the two chambers. The acoustical stiffness of the system at low
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