Source: https://patents.justia.com/patent/5305384
Timestamp: 2019-06-17 21:33:24
Document Index: 66887039

Matched Legal Cases: ['art 22', 'art 2', 'art 22', 'art 22', 'art 2', 'art 22']

US Patent for Apparatus, system and method for transmitting secure signals over narrow spaced channels Patent (Patent # 5,305,384 issued April 19, 1994) - Justia Patents Search
Justia Patents Nbs/des AlgorithmUS Patent for Apparatus, system and method for transmitting secure signals over narrow spaced channels Patent (Patent # 5,305,384)
Sep 9, 1992 - Chips International, Inc.
Latest Chips International, Inc. Patents:
As stated above and discussed in U.S. Pat. No. 4,852,166, another problem that typically arises in conventional digital voice encryption devices is that the transmitted BPS rates require transmission of frequency components that exceed the voice pass-band of 3200 Hz (approximately 300 to 3,200 Hz) specified by the FCC for conventional and trunked analog radio and telephone systems. One such system is described in U.S. Pat. No. 4,817,146. Patent '146 specifies a fairly high transmitted frequency component of approximately 7200 Hz. To compensate for the transmitted high frequencies, a low pass filter is modified or bypassed in the radios and the level of modulation deviation is often lowered to remain within the approved occupied bandwidth of 15 KHz to 25 KHz spaced channels. Oftentimes, lowering the modulation deviation results in a reduction of transmitter efficiency. To compensate for a loss of transmitter efficiency, radio transmitter power must generally be boosted. As shown in the FCC Rules and Regulations, Title 47 Code of Federal Regulations (CFR) Part 22.508 dated Oct. 1, 1988, a low-pass filter is required before the modulator in a conventional and trunked radio that attenuates audio frequency components above the voice pass-band from 3 KHz to 15 KHz by at least a scale of 40 log.sub.10 (f/3) decibels (db) where "f" is the audio frequency in KHz. Thus, the digital encryption device described in Patent '146 (which transmits a 7200 Hz high frequency component), must modify or bypass this low-pass filter because the transmitted signal strength (power) of the high frequency component would be attenuated by approximately 15 db below the low frequency component (i.e., 2400 Hz). This would result in a conventional radio only transmitting the high frequency component at a power level substantially equal to 1/32nd of the low frequency component transmitted power, rendering the device virtually useless.
Also, as discussed in the FCC Rules and Regulations Part 2.202 dated Oct. 1, 1987 and Part 22.507 dated Oct. 1, 1988, the formula to calculate the necessary bandwidth occupied by a typical FM radio emission is B.sub.n =2M+2DK, wherein:
B.sub.n =necessary bandwidth in hertz.
B.sub.n =2(7200 Hz)+2(10000 Hz/2)(1)
B.sub.n =14400 Hz+10000 Hz
B.sub.n =24400 Hz or 24.4 KHz
B.sub.n =2(7200 Hz)+2(5000 Hz/2)(1)
B.sub.n =14400 Hz+5000 Hz
B.sub.n +19400 Hz or 19.4 KHz
While it is noted that the frequency components are not totally within the 300 Hz to 3,000 Hz range, the selection of 6,400 BPS as the preferred voice data rate with a corresponding 3,200 Hz high frequency component is the result of a trade-off that gains 400 BPS forward-error correction for a less than 10 percent signal loss. Using the formula 40 log.sub.m (f/3) decibels for the low pass filter as defined above in FCC Rules and Regulations Part 22.508 dated Oct. 1, 1988, the signal level of the high frequency component of 3,200 Hz will be approximately 1 db lower than the other frequency components. This is expected to cause negligible signal loss in return for a gain of 400 BPS forward-error correction. It should be noted that the BPS rate can be lowered to remain totally within the voice passband of 300 to 3,000 Hz. However, as can be appreciated by those skilled in the art, since the low pass filter only attenuates the signal, practically speaking the transmission of a 3,200 Hz frequency component is within the voice passband.
Also, it should be noted that when using MFM at a 6,400 BPS rate which transmits a 3,200 Hz highest frequency component, the entire bandwidth for 15 KHz to 25 KHz spaced channels is not necessary. Using the formula B.sub.n =2M+2DK defined above in the FCC Rules and Regulations Part 2.202 dated Oct. 1, 1987 and Part 22.507 dated Oct. 1, 1988, the necessary bandwidth for a 3,200 Hz highest frequency component should be as follows:
B.sub.n =2(3200 Hz)+2(10000 Hz/2)(1)
B.sub.n =6400 Hz+10000 Hz
B.sub.n +16400 Hz or 16.4 KHz
B.sub.n =2(3200 Hz)+2(8000 Hz/2)(1)
B.sub.n =6400 Hz+8000 Hz
B.sub.n +14400 Hz or 14.4 KHz
B.sub.n =2(3200 Hz)+2(5000 Hz/2)(1)
B.sub.n =6400Hz+5000 Hz
B.sub.n +11400 Hz or 11.4 KHz
PGA 20 thereby replaces numerous standard logic circuits and reduces the manufacturing cost and inventory cost of the present device 10. PGA 20 also decreases the power requirements for device 10 and is completely re-programmable if interconnect changes must be made. Configuration changes can be made through a serial programmable read only memory (not shown) connected to PGA 20 in order to load PGA 20 with its start-up configuration. Serial programmable read only memory (SPROM) can be purchased from Advanced Micro Devices, model no. AM1736A-DC. This SPROM is a one-time programmable device and the format used to store the information in SPROM is proprietary to XILINX R.RTM..
In order to restrict unauthorized operation of device 10, the mode selector can be replaced by a high security key switch, such as a MEDECO.RTM. keyswitch. The front panel 28 communicates with the CPU 16 through use of one of the parallel input/output device PIOs (not shown) located near the front panel. A preferable PIO device may be purchased from ZILOG Corporation, part no. Z84C2010FEC. Thus, a plurality of different front panel controls can be implemented such as a remotely mounted and controlled unit incorporating a control head placed at a different location than device 10 main unit.
5007050 April 9, 1991 Kasparian et al.
5150401 September 22, 1992 Ashby et al.
Patent number: 5305384
Assignee: Chips International, Inc. (Priddy, TX)
Inventors: James C. Ashby (Priddy, TX), Clark Burkhart (Azle, TX), Frankie Favors (Bedford, TX), Roy G. Tiemann (Priddy, TX), Robert L. Vandaveer (Granbury, TX), Lothar A. Krause (Irving, TX)
Law Firm: Daffer & Associates
Application Number: 7/942,661
Current U.S. Class: Nbs/des Algorithm (380/29); Particular Algorithmic Function Encoding (380/28); Plural Modulation Of Single Carrier (380/31); Using Plural Paths Or Channels (380/33)