FED-STD 1023
3.2.3 V.F. Filter. The V.F. Filter should have an attenuation at 6 kHz and higher frequencies relati ve to frequencies between 300 and 3,000 Hz of at least 20 dB. It
is recommended that the filter be essentially flat (i.e., ~3 dB) between 300 and 3,000 Hz.
3.2.4 Comparator. The binary digital output of the Comparator shall be either ONE
or ZERO, depending upon whether the amplitude of the input voice signal is
greater than or less than the output of the Principal Integrator.
3.2.5 Modulation Level Analyzer. The Modulation Level Analyzer (MLA) shall charge the MLA Integrator whenever the last and two immediately preceding bits
from the Comparator are either all ONEs or all ZEROs (i.e., there is run -of-three coincidence).
3.2.6 MLA Integrator. The MLA Integrator (often called Syllabic Filter) provides pulse amplitude information to the Pulse Modulator. The change in pulse
amplitude from one bit time to the next (i.e., quantizing step size) should vary, in a linear manner, from a run -of-three coincidence rate of 0 percent to a rate of 50
percent by a voltage ratio of approximately 10 to 1 (i.e., 20 dB). The time constant of the MLA Integrator shall be 6~2 ms.
3.2.7 Pulse Modulator. The pulse modulator shall create pulses using amplitude information from the MLA Integrator and polarity information from the
Comparator.
3.2.8 Principal Integrator. The Principa l Integrator shall have a time constant of 1+.25 ms.
3.3 Encryption
3.3.1 Encryption Algorithm. Encryption of the digitized voice shall be accomplished with the encryption algorithm used in the INDICTOR and WINDSTER
COMSEC Modules (see references a and b) using the cryptographic mode that has cryptographic compatibility with the KY-57/58. (Other compatible
implementations may be substituted.)
3.3.2 Encryption Operating Mode. The encryption process shall use the cryptographic operating mode of the INDfCTOR and WINDSTER COMSEC
Modules designated for compatibility with the KY -57/58. (Other compatible implementations may be substituted.)
3.3.3 Cryptographic Synchronization
3.3.3.1 Synchronization Check Bits. Transmitting radios shall predictably force synch ronization check bits in the unencrypted digitized voice, prior to encryption,
as is done by the KY-57/58 (see reference a (section 5.3, paragraph 2) and reference c). Receiving radios shall utilize these predictable synchronization check
bits to determine whether cryptographic synchronization has been lost (see reference a, section 5.3.3, paragraph 3).
3.3.3.2 Alternating ONE/ZERO Pattern. Continuously Variable Slope Delta-modulation (CVSD) should inherently produce an alternating binary ONE/ZERO
pattern during the idle condition (i.e., pauses in speech). In order to promote rapid initial synchronization and resynchronization, transmitting radios shall ensure
that a segment of alternating ONE/ZERO pattern at least 95 percent the length of the segment produ ced by the KY -57/58 (see reference c) is produced in the
unencrypted bit stream, prior to encryption, at least once every two seconds. All receiving radios shall be capable of initial synchronization and subsequent
resynchronization (after detecting absenc e of synchronization check bits) utilizing segments of alternating ONE/ZERO pattern in the decrypted bit stream.
3.3.4 End-of-Message Sequence. Radios shall transmit the same encrypted End -of-Message sequence used by the KY -57/58, with a duration between 60 and
120 percent of that transmitted by the KY-57/58, at the end of each half-duplex transmission, followed by 160+10 ms of unencrypted alternating ONE/ZERO
pattern, to mark the end of a transmission. (Note: this -is to assist encryption equipment and re peaters in distinguishing between a fade condition and an actual
end of transmission.)
3.3.5 Additional Non-voice Sequences. Radios may employ additional, unspecified, non-voice sequences at the start of transmissions (e.g. KY-57/58 initial
synchronization). However, use of these additional sequences shall not impair interoperation with radios not utilizing such additional sequences.
3.4 Modulation Deviation and Coding. Transmitter deviation shall be ~4 kHz (~10 percent) from the carrier frequency. Receiving radios shall operate
satisfactorily regardless of whether transmitted binary ONEs (or ZEROs) were coded as positive or negative 4 kHz shifts in carrier frequency.
3.5 Spectrum Standards. Applicable spectrum standards for Federal Government radio communication systems are given in Chapter 5 of the National
Telecommunications and Information Administration's (NTIA) "Manual of Regulations and Procedures for Radio Frequency Management", 47 Code of Federal
Regulations Part 300.
4. EFFECTIVE DATE. The use of this standard by U.S. Government departments and agencies is mandatory effective 270 days following the date of this
standard.
5. CHANGES. When a Government department or agency considers that this standard does not provide for its essential needs, a statement citing specific
requirements shall be sent in duplicate to the General Services Administration (K), Washington, DC 20405, in accordance with the provisions of Federal
Information Resources Management Regulation 41 CFR 201 -13.103. The General Servi ces Administration will determine the appropriate action to be taken and
will notify the agency.
PREPARING ACTIVITY:
National Communications System
Office of Technology and Standards
Washington, DC 20305-2010
MILITARY INTEREST:
Review Activities
Military Coordinating Act ivity
DCA C
Army -- SC, CR
Navy -- EC, MC
Air Force -- 02, 17
Custodians
Army -- SC
NSA n NS
Navy -- EC
JTC3A -- JT
Navy -- EC
Air Force 90
U.S. GOVERNMENT PRINTING OFFICE: 1990-0-704.QOO/00023
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