<communications> A kind of telegraphy system developed by Thomas A. Edison in the 1870s combining diplex and duplex communications to support simultaneous transmission of two messages in each direction. (2000-04-02)

2-inch quadruplex videotape (also called 2″ quad video tape or quadraplex) was the first practical and commercially successful analog recording video tape format. It was developed and released for the broadcast television industry in 1956 by Ampex, an American company based in Redwood City, California.

The Quadruplex telegraph is a type of electrical telegraph which allows a total of four separate signals to be transmitted and received on a single wire at the same time (two signals in each direction). Quadruplex telegraphy thus implements a form of multiplexing.

In molecular biology, G-quadruplex secondary structures (G4) are formed in nucleic acids by sequences that are rich in guanine. They are helical in shape and contain guanine tetrads that can form from one, two or four strands.

Cryptocephalus quadruplex is a species of case-bearing leaf beetle in the family Chrysomelidae. It is found in North America.

Coleophora quadruplex is a moth of the family Coleophoridae. It is found in North America, including Nova Scotia, Illinois, Maine, Massachusetts and New York.

Belomitra quadruplex is a species of sea snail, a marine gastropod mollusc in the family Belomitridae, the whelks.

Duplex telegraphy is the sending of two messages in opposite directions simultaneously through the same wire. Duplex telegraphy is the sending of two messages simultaneously in the same direction. The two combined constitute quadruplex telegraphy. [SIC] The system was suggested by Stark of Vienna and Bosscha of Leyden in 1855; the successful problem was solved by Edison in 1874. The principle is based on the two orders of difference in electric currents; they may vary in strength or in direction. Thus we may have one instrument which works with change of strength of current only, the other with change of direction only. The two can be worked together if the direction of the current can be altered without alteration of strength, and if strength can be altered without alteration of direction. Double current and single current working are so combined that one relay works by one system of currents and another relay by the other system. A current is constantly maintained through the line. The relay operated by change in direction is a simple polarized relay which works by change of direction of current. The relay operated by change in strength is the ordinary unpolarized relay. For the following description and the cuts illustrating it we are indebted to Preece and Sivewright. The cut shows the arrangement of the apparatus and connections for terminal offices. "Sufficient table room is provided to seat four clerks. The apparatus is arranged for the two senders to sit together in the centre, the messages to be forwarded being placed between them. The section on the left of the switch Q is known as the 'A' side, that on the right as the 'B' side of the apparatus. K1 the reversing key, reverses the direction of the current. K2 is a simple key, known as the increment key; it is used simply to increase the strength of the current. Fig. 320. QUADRUPLEX TELEGRAPH CONNECTIONS. The way in which the keys K1 and K2 combine their action is shown by Fig. 321. E1 and E2 are the line batteries, the one having two and one-third (2-1/3) the number of cells of the other, so that if E1 be the electro-motive force of the smaller, that of the whole combined battery will be 3.3 E1. The negative pole of E1 is connected to z and z1 of  K1 and the positive pole of E2 to a of K2 through a resistance coil s. A wire, called the 'tap' wire, connects the positive pole of E1 and the negative pole of E2 to b of K2. This wire has in it a resistance coil r2. The springs c and c1 of Kl are connected to the lever L of K2. Now, when both keys are at rest, the negative pole of E1 is to line through z, and the positive pole of E1 to earth through b of K2 and c of K1; the positive pole of E2 being insulated at a of K2. There is thus a weak negative current flowing to line. When K1 alone is worked, the current of E1 is reversed. When K2 is worked alone, c of K1 is transferred from b to a, and the strength of the negative current going to line is increased through the increase of the electro-motive force from E1 to 3.3 E1 for the whole battery is brought into play. When K1 and K2 are depressed together, then the negative pole of E1 goes to earth through Z1; and the positive pole of E2 to line through a of K2 and c1 of K1 and a positive current, due to the whole electro-motive force 3.3 E1 goes to line. Hence the effect of working K1 is simply to reverse the current, whatever its strength, while that of K2 is to strengthen it, whatever its direction. The resistance coil s, of 100° resistance, is called a spark coil, because it prevents the high electro-motive force of the whole battery from damaging the points of contact by sparking or forming an arc across when signals are sent; and the resistance r2 is made approximately equal to the combined resistance of E2 and the spark coil, so that the total resistance of the circuit may not be altered by the working of the apparatus. Fig. 321. QUADRUPLEX TELEGRAPH. A1 and B1 (Fig. 320) are the relays which are used to respond to the changes in the currents sent by the keys K1 and K2 at the distant station. A, is a simple polarized relay wound differentially, each wire having a resistance of 200 [omega], and so connected up as to respond to the working of the reversing key K1 of the distant station. It acts independently of the strength of the current, and is therefore not affected by the working of the increment key K2. It is connected up so as to complete the local circuit of the sounder S1 and the local battery l1 and forms the receiving portion of the 'A' side. B, is a non-polarized relay also wound differentially, each coil having a resistance of 200 [omega]. It responds only to an increase in the strength of the current, and therefore only to the working of the increment key K2 of the distant station. [Transcriber's note: In current usage upper case omega indicates ohms and lower case omega denotes angular frequency, 2*PI*f.] The relay spring is so adjusted that the armatures are not actuated by the weak current sent from E by the key K1. In its normal position this relay completes the circuit of the local battery through the sounder S. This sounder S, called the uprighting sounder, acts as a relay to a second sounder, S2, called the reading sounder, which is worked by another local battery, l2. Of course, normally, the armature of S is held down and that of S2 is up, but when the tongue t moves, as it does when the increment key K2 is depressed so as to send the whole current to line, then the current from l is interrupted, and the circuit of l2 is completed by the rising of the armature of S, causing the reading sounder S2 to work. This is the 'B' side. R is a rheostat for balancing the resistance of the line, as used in duplex working. C is a condenser used for compensating the static charge of the line. It is provided with an adjustable retardation coil, R1, to prolong the effect of the compensating current from the condenser. G is a differential galvanometer, used for testing, and for facilitating adjustment and balancing. Q is a switch for putting the line to earth, either for balancing, or for any other purpose. There is on the earth wire leading from Q a resistance coil, r1, equalling approximately the resistance of the whole battery, 3.3 E1, and the resistance s. The connections shown in Fig. 321, are for an 'up' office. At a 'down' office it is necessary to reverse the wires on the two lower terminals of the galvanometer and the two battery wires on the reversing key K1. The keys K1 and K2 are, for repeaters, replaced by transmitters. The adjustment of this apparatus requires great care and great accuracy. Its good working depends essentially on technical skill that can only be acquired by patience and perseverance. Faults in working generally arise from careless adjustments, dirty contacts, loose connections, battery failures, and the ordinary line interruptions, but there are no troubles that are beyond the reach of ordinary skill, and it can be safely said that, within moderate distances, wherever and whenever duplex working is practicable, then quadruplex working is so too." The above is a typical quadruplex bridge system. There is also a differential system, the full description of which, in addition to what has been given, is outside of the scope of this work.