The arrangement on the " open-circuit " system for single-current working is shown in fig.
It will be observed that the circuit is not in this case actually open; the meaning of the expression " open circuit " is " no battery to line."
It differs from the open circuit in only requiring one battery (although, as in the figure, half of it is often placed at each end), in having the re circuit ceiving instrument between the line and the key, and in having the battery continuously to the line.
When signals are to be sent from either station the operator turns the switch c out of contact with the stop b, and then operates precisely as in open circuit send '" i ing.
D and spark gap, has the same natural time period of oscillation as the open circuit consisting of the antenna, secondary coil and adjustable inductance.