419,526. Wireless signalling; controlling telegraph traffic. BAKKER, A., 207, Theresiastrasse, Haag, and DUUREN, H. C. A. VAN, 18, Heerenweg, Noordwijkerhout, both in Holland. May 9, 1933, No. 13504. [Classes 40 (ill) and 40 (v).] A telegraph system using different currents for marking and spacing is provided with a protective device which protects the receiving apparatus against unnoticed reproduction of faulty signals due to atmospherics or fading. In the system of Fig. 1, marking and spacing elements represented by different frequencies are separated by filters 4, 5 and applied to rectifiers 6, 7 respectively, in whose outputs are relays 8, 9. When relay 8 is operated and relay 9 is inoperative, current passes from battery 12 to a line 10 connected to the receiving printing device, whilst with relay 9 operated and relay 8 inoperative no current passes to the printing device. When the armatures are both against contact r owing to fading or against contact w owing to atmospherics the protective relay 11 is operated and in addition an impulse passes to the recording device connected to the line 10, so that the disturbed reception is positively indicated. In an alternative form, Fig. 2, if interference occurs so that both armatures are against their working or resting contacts no current passes to the recording device, the batteries 12, 13 being in opposition when the armatures of relays 8, 9 are both in resting or working positions. In a further arrangement, (Fig. 3, not shown) a relay has two windings individually connected to two rectifiers similarly arranged to the rectifiers 6, 7 of Fig. 1. If interference occurs the currents in the windings are in opposition or are individually zero and with the armature in its neutral position no current passes to the line leading to the receiver. Fig. 4 shows a station adapted for reception and transmission in connection with a similar station by the operation of synchronized distributers 1, 2, respectively and utilizing interference relays as described in connection with Fig. 1. Signals transmitted from segments 26-30 by a distant station B are received at station A over segments 7-11 and passed to a receiving member 12 provided with an interference relay. If no interference occurs relay 13 is not energized and the telegraphic receiving device receives a start impulse over contact 14 and a contact (not shown) of the distributer. Over contact 16 of a relay 17 which is not energized the A-station transmitting device sends a start impulse to a distant station B where it is received by a device 20 constructed as a protective device and provided with an interference relay 21. If the impulse is received undisturbed, relay 21 is not energized and the transmitting apparatus 22 is set into operation, setting up a new code combination, and the next signal is transmitted from segments 26-30 of the station B. The resting contacts of transmitter 22 at the station B are connected at 24 to positive battery and working contacts are connected through the resting contact of relay 21 to a negative source. If any element of the received signal at station A is disturbed, relay 13 pulls up, opening the circuit of the printer 15 and operating relay 17 so that its armature 16 sends a negative (marking) impulse. At the distant station the device 20 itself interrupts the starting circuit for the transmitter 22 so that no new signal is transmitted, and the previous signal is therefore repeated. If the warning signal is disturbed, relay 21 at the station B pulls up, opening contact 23 in the starting circuit of transmitter 22 and applying positive to the contacts of the transmitting tongues and to the contact 31 of the transmitter. If the warning signal has not been disturbed, a negative (marking) impulse is transmitted from 25 to 31 and at station A this is received by a protective device 33. If a marking impulse or an interference is received by.33, the circuit of relay 17 is closed to earth and through resting contact 34 of relay 35. If the special signal is of spacing current the circuit to relay 17 is interrupted within 33. A relay 35 is energized if undisturbed reception of the five positive impulses transmitted from the distant station has taken place. If a positive impulse has been received by the device 33, at station A relay 17 is unaffected by the signal received in 12 since its circuit is interrupted. Station A at 18 retransmits the warning signal, and if it arrives undisturbed by 20 at the distant station, the previous signal or a fresh signal is transmitted, as the case may be. A protective device as described in connection with Figs. 2, 3 may be incorporated in a system employing multiple transmission. As shown in Fig. 5, the contacts 21, 22, 23, corresponding to a signal element, are closed in accordance with the multiple transmission. A condenser 26 is charged positively or negatively during the closing of the contacts unless each transmission is disturbed, and on the closure of contact 24 the condenser, if charged, will actuate a polarized relay 27 and relay 28 so that a positive or negative impulse is transmitted to the printing apparatus, and the device indicating disturbed reception is disconnected. In a further arrangement, Fig. 6, the impulses are passed to a chain of relays equal in number to the number of transmissions. If an undisturbed impulse is received, relay 41 is energized when contact 31 is closed and locks up over contact 36. Polarized relay 42 also is energized and at contact 37 the windings of relays 43 and 44 are connected to the armature of relay 42. When the distributer closes contact 32, relays 43, 44 are energized, opening contact 40 leading to the protective indicating device and passing the impulse from relay 44 to the receiving printing device. If the first transmission is disturbed while the second transmission is free from disturbance, relay 41 is not energized but relay 43 is energized from the line 35. If both transmissions are disturbed, relay 43 is not energized and since the circuit of the indicating protective device is not interrupted a special sign is printed by the telegraph receiver. In a further modification, (Fig. 7, not shown) using multiple transmission and perforated tape, the perforations according to marking and spacing elements are on separate transverse lines of the tape so that an impulse is recorded if it is received without disturbance in one of the multiple transmissions. No perforation is effected for an element which is disturbed during each of its transmissions.