Teletype character modification unit
AssigneeThe United States of America as represented by the Secretary of the Army
InventorsGerald Weiss, Gerson Scharf, Anthony A. Guido, Benjamin Lazardwitz
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AssigneeThe United States of America as represented by the Secretary of the Army
InventorsGerald Weiss, Gerson Scharf, Anthony A. Guido, Benjamin Lazardwitz
Estimating the term…
3. A teletype modification unit comprising: a signal shaper having input ns for receiving mark-space teletype pulses; a synchronization circuit coupled to said signal shaper; a plurality of delay means coupled to said synchronization circuit; a space coincidence circuit; a mark coincidence circuit; means to selectively couple said plurality of delay means to said space coincidence circuit, and means to selectively couple said plurality of delay means to said mark coincidence circuit.
A teletype baud modification unit comprising:
A teletype baud modification unit comprising:
A teletype modification unit comprising:
A teletype character modification unit comprising:
A teletype character modification unit comprising:
A teletype character modification unit comprising:
A teletype character modification unit comprising:
A teletype character modification unit comprising:
A teletype character modification unit comprising:
Dependencies are inferred from the claim text.
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This invention relates to a countermeasures or coding system for use with frequency shift keyed radio teletype transmission, and more particularly relates to a teletype "baud" modifier unit.
The prior art discloses various systems for jamming a radio signal. Perhaps the most common method of disrupting enemy communications of any character is by blanketing the victim's signal with continuous high power signals. The signals are usually modulated by some means such as a noise generator. This technique requires a large power output from the countermeasures transmitter and is readily detected. Furthermore, it prevents monitoring the victim's signal during jamming because any receiver in the vicinity of the jamming transmitter is blanketed as effectively as the victim receiver.
We have invented a jamming method that is efficient from the standpoint of countermeasures transmitter output power, and the victim cannot readily detect the jamming signal under normal operating conditions. In addition, a continuous copy of the victim's signal can be received at the countermeasures site even during the jamming periods. The countermeasures system is the subject matter of copending application Ser. No. 171,320 filed Feb. 5, 1960 and assigned to the assignee of this invention.
These and other objects will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a teletype code chart.
FIG. 2 is a block diagram of a countermeasures system.
FIG. 1 is a teletype code chart having the letters arranged in binary sequency. The dark portions of the chart indicate marks and the light parts are spaces. All the teletype characters start with a space and end with a mark (i.e. start - stop pulses). The remaining five bauds or time intervals are used to establish the characters. From the chart it is apparent that some of the teletype characters fall into groups having similar mark-space sequences. For example the letters "x" through "E" all have a mark in the first interval and a space in the second interval. Likewise the characters "V" through "line-feed" all have a space in the first interval and a mark in the second interval. As will become apparent later, it is the ability to group the characters having similar mark-space sequences that makes selective modification of a teletype message possible.
FIG. 2 shows a complete countermeasures system. As was mentioned above, this system is the subject matter of another application; however, a brief description of the system will facilitate a clear understanding of the operation of the modification unit. The teletype message that is to be altered is transmitted at the victim's transmitting terminal 130. Radio receiver 123 at countermeasure terminal 128 receives the victim's message and applies the frequency-shift signal to converter 126. The converter changes the frequency-shift signals to mark-space current pulses. The current pulses are applied to modification unit 127. The modification unit is programmed to make either random or selected changes in the baud structure of the victim's message. For example, assume that only those letters having a mark in the first interval and a space in the second interval are to be changed. Also assume that only the marks after the second interval are to be changed. That is, all the marks after the second interval are to be changed to spaces and the spaces are not changed. If the letter "D" is received, it will be changed to the letter "E". As soon as unit 127 makes the change, receiver 123 is disabled and exciter 121 keys transmitter 122. Transmitter 122 sends out a space pulse which is received at the victim's receiving site 129. The space pulse transmitted by transmitter 122 is of sufficient amplitude to blanket the mark pulse originally transmitted by the victim transmitter. Due to the time delay introduced by the countermeasures equipment the pulse transmitted by transmitter 122 is received by the victim's receiver a short time after the leading edge of the original mark pulse is received; however, this time delay is too short for the victim's receiving equipment to sense the pulse from the victim's transmitter rather than the pulse from transmitter 122. The bandwidth of a teletype receiver is generally inherently narrow to limit noise interference and to conserve spectrum space. Thus, any pulse which occupies the major portion of a normal baud will satisfactorily operate the teletype receiving equipment, and slight variations in pulse width are relatively unimportant. The pulse from transmitter 122 has a slightly shorter time duration than a standard teletype pulse so that it will not overlap the succeeding pulse.
Transmitter 122 is on the air only when modification unit 127 changes the baud structure of the victim's message. This intermittent keying of the transmitter results in a much smaller power consumption than is normally used by a countermeasures system.
Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols: countermeasures against…
Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols: transmitting and receiving…
Digital communication
Term ended 4 Nov 1997 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.