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Home  Telegraph Systems The Bridge Duplex System |
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The Bridge Duplex SystemThe bridge duplex system is based on the principle of the Wheatstone bridge, as is evident from Fig. 10. When the operator at the west station presses the key for telegraphing to the east station, the pole-changing relay for sending the "double" current is pulled to the left, sending a current impulse out on the line as shown by the arrows. If the impedances of coils L1 and L2 are identical and if the west artificial line exactly balances the impedance of the connecting line and the entire east set, then I1 and I2 will be equal, the bridge will be balanced (page 74), and no current will flow through the west polar relay. Thus, the relay and the sounder at the west sending station will not operate when this station is sending. There are three paths for the current I1 through the receiving equipment as indicated by the arrows at the east station. Of these three paths, the current through the polarized relay will cause it to operate if the current is of the proper polarity.
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Last Update: 2011-05-27