Title:
Dle time keying
United States Patent 2132124


Abstract:
This invention relates to idle time keying circuits for use with printing telegraph apparatus on radio circuits. This application Is a division of my U. S. application Ser. No. 703,783, filed Dec. 23, 1933 now Patent No. 2,055,985, issued Sept. 29, 1936. In communication by radio, it is frequently...



Inventors:
Peterson, Harold O.
Application Number:
US5805536A
Publication Date:
10/04/1938
Filing Date:
01/08/1936
Assignee:
RCA CORP
Primary Class:
International Classes:
H04L7/00
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Description:

This invention relates to idle time keying circuits for use with printing telegraph apparatus on radio circuits. This application Is a division of my U. S. application Ser. No. 703,783, filed Dec. 23, 1933 now Patent No. 2,055,985, issued Sept. 29, 1936.

In communication by radio, it is frequently necessary in order to maintain circuit contact, for the attendant at the receiving station to check the tuning adjustment of the receiver with the transmitter. When message signals are being sent over the radio channel, it is the practice to utilize these same signals for the supervision of the circuit, but during idle periods it is customary to transmit frequency test signals to maintain a continuous assurance that the overall circuit is functioning; otherwise, some adjustment of either the transmitter or receiver might change during the idle period, a condition which bnight consequently result in no response at the receiver when the transmitter resumes operation.

Heretofore, in the use of automatic Morse code telegraph transmitters, it has been customary to send V's, dots, ABC's or call letters at spaced intervals during idle periods. Such procedure, however, has not proven convenient on printer circuits; consequently, it has been the practice to use reversed keying. In this type of operation, the marking Impulses appear as spaces on the transmitted signal. Thus, a steady dash will be sent during the Intervals between transmissions.

While the radiation of a steady dash between transmissions proves to be a very effective way of maintaining circuit contact, it has been found to constitute a continuous dissipation of power and wear and tear on the transmitter tubes.

It is the primary object of the present Invention to provide means whereby circuit contact may be maintained without such objectionable dissipation of power and wear on transmitting equipment.

According to the present invention, it is proposed to transmit letters from the printer equipment at even intervals at a rate of approximately 24 letters per minute, a number which it is found maintains satisfactory contact over the circuit.

The keying is arranged so that the transmitter radiates energy only during the marking impulses from the printer. Since the full speed transmission rate for a typical printer is 372 letters per minute, and since the marking Impulses represent only a portion of the signaling time, it will be seen that a considerable saving of power and tube life may be obtained by the use of a device for sending a reduced number of letters, let us say, approximately 24 spaced letters per minute. The number of these spaced letters per minute may, of course, be varied to suit circuit conditions and in some cases the number considerably reduced.

The invention is accomplished, in accordance with one embodiment, by the provision of automatic apparatus for causing the transmission of the test letters, this apparatus being attached directly to the keyboard for movement of any letter key. In a specific embodiment, apparatus is connected to the mechanical or the electromechanical parts of the printer itself whereby the desired letters are transmitted by the automatic operation of the clutch lever or the "trip-off pawl" of the mechanism. Other embodiments will readily suggest themselves from a reading of the specification.

One feature of the invention is an indicator arrangement in the form of a photoelectric scanning device at the receiver for actuating an alarm whenever there are received letters other than the predetermined test letter.

The invention is described in more detail in the accompanying specification which is accompanied by a drawing wherein: Figures 1 and 2 schematically illustrate different embodiments of the invention; and Fig. 3 shows an alarm device at the receiver for attracting the attention of the attendant whenever the successive printing of test letters is interrupted.

Referring to Fig. 1, there is shown a standard printer I in circuit with a line 2 extending to a radio transmitter 3 arranged to radiate energy over an antenna 4. Fixedly attached to the printer by means of a suitable bracket frame support 5 is a plunger device 6 which acts on any desired letter key. This plunger is operated upon by a cam 7 which is located on a shaft 8 geared through reduction gears 9 to a motor 10, current for which is supplied over leads fl. The end of the plunger is covered with a soft material, such as rubber, and its position is adjusted so as to depress the key a desired amount. A spring 12 serves to return the plunger to normal. In the operation of the device during idle time intervals, rotating cam 7 functions to periodically cause the plunger to depress the desired key a certain number of times per minute whereby test letters are transmitted by the printer over line 2 to the distant radio transmitter from which the signals are sent out to the antenna 5.

Figure 2 illustrates a further modification wherein the idle time keying device operates on the mechanical parts of the well known Klein- B5 schmidt printer 26. Since the printer itself forms no part of the invention per se, only that portion of the printer is shown which is necessary for a proper understanding of the invention. The drawing shows in part a vertical crosssection of the printer wherein an electromagnet 28 acts to pull forward the "trip-off pawl" 21, whereupon the printer transmits the test character as determined by the last setup of the selector bars which remain in the position determined by the last letter sent out by the printer by the operation of the printer keys in the normal manner.

Similarly, it is possible to cause, by means of 18 an electromagnet or a mechanically actuating device, periodic deflections of the clutch lever pawl which would cause transmission of spaced letters.

The electromagnet 28 Is controlled by means of a commutator driven by a motor, as shown.

The actuating impulses as applied to the electromagnet 28 may, if desired, be derived from any suitable generator as, for example, a multivibrator circuit, a glow tube oscillator, or the like. It is also evident that the same effect can be obtained by mechanical means such as, for example, pneumatic drives, mechanical links, etc.

In Fig. 3, is shown a photoelectric scanning device for automatically actuating an alarm whenever the receipt of test letters is interrupted.

Assuming in this case that the test character is the punctuation mark "period", the photocell will receive sufficient light reflected by a strip of tape 30 (bearing a string of spaced black dots representing periods) from a source of light 31 to cause the energization and operation of a relay 32 in the anode circuit of an amplifier 33. When other characters such as letters appear on the tape the amount of black markings will increase and less light will be reflected, upon the occurrence of which the anode current in the amplifier will be reduced and relay 32 will fall back to close a circuit operating the alarm 34.

The embodiments of the invention illustrated and described herein have been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet different conditions encountered in its use, and S5 it is, therefore, aimed to cover by the appended claims all modifications within the spirit and scope of the invention.

What is claimed is: 1. In combination, a transmitting printer, a transmission system connected therewith, periodically operated means operatively associated with said printer for causing said printer to transmit idle period impulses at intervals greater than the normal intervals between impulse char- 8 acters used when said printer is transmitting intelligence bearing signals, the character of said idle period impulses being determined by the last setup of the printer in the transmission of signal message characters, and means for putting said periodically operated means in operation during idle periods.

2. In combination, a transmitting printer, a periodically operated electromagnet operatively associated with said printer for causing said 18 printer to transmit idle period characters at Intervals greater than the normal intervals between characters used when said printer is transmitting Intelligence bearing message signals, said idle period characters being determined by the last setup of the printer in the transmission of message signals, and means for putting said periodically operated means in operation during idle periods.

3. In combination, a transmitting printer, periodically automatically operated means operatively associated with said printer for causing said printer to transmit idle period characters at intervals greater than the Intervals between characters used when said printer is transmitting intelligence bearing message signals, said characters being determined by the last character sent out by the printer in the transmission of message signals, and means for putting said periodically operated means in operation during idle periods. 4. In combination, a transmitter-printer Including keying mechanism for producing impulses characteristic of messages to be transmitted, said mechanism comprising a tripoff pawl, and means for sending out impulses at relatively long intervals during idle periods of said printer including an electromagnet comprising a winding which may be periodically energized, an armature associated with said magnet, and a link connecting said armature to said tripoff pawl. 48 5. In a start-stop printing telegraph system, circuit arrangements for transmitting code signals in response to the actuation of the keys of said system, means operatively connected to said circuit arrangement for slowly repeating the O0 final code signal of a message during idle periods of said system, and manually control means for rendering the repeating means effective.

HAROLD 0. PETERSON.