| 摘要 |
PHN 8782 3.3.78 An electronic transmitter for direct current telegraphy by means of polar line currents comprises a switching circuit for selectively connecting one of the two poles of a telegraphy battery through a unipolar constant current source to a telegraph line, and an output filter having a capacitor in parallel with the telegraph line. The higher frequencies in the telegraphy signals are sufficiently suppressed to keep the noise level in adjacent telephone lines below a prescribed value because the output filter also comprises two complementary branches in parallel with the telegraph line, at least one of the two branches supplying, in response to a polarity transition of the line current supplied by the current source, a correction current pulse having a polarity opposite to the line current to the telegraph line. This output filter is assembled from smallsized, low-priced elements so that an efficient miniaturisation of the electronic transmitter in its entirety can be realized. |
