[T]he service area of a broadcast station served by the skywave and not subject to objectionable interference and in which the signal is subject to intermittent variations in strength. [47CFR]

In a communications network, a station that (a) is responsible for performing unbalanced link-level operations as instructed by the primary station and (b) interprets received commands and generates responses.

Synonym secondary radar.

A time standard that requires periodic calibration against a primary time standard.

Acronym for secure voice cord board. A desk-mounted patch panel that provides the capability for controlling (a) sixteen 50-kb/s wideband or sixteen 2400-b/s narrowband user lines and (b) 5 narrowband trunks to DSN or other narrowband facilities.

1. A key that is intended for use by a limited number of correspondents for encryption and decryption. [2382-pt.8]
2. In a symmetric cryptographic algorithm the key shared between two entities [10181-1].
3. In a symmetric encipherment algorithm the key shared between two entities [10181-2].

Any encryption process that (a) depends on only one encryption key, known only to message senders and receivers, and (b) is used to both encode and decode the message. [After Mattila]

Acronym for secure telephone. See STU.

The portion of a transmission facility, including terminating points, between (a) a terminal network element (NE) and a regenerator (for example, a central office/remote terminal and customer location equipment such as a DTE) or (b) two regenerators. A terminating point is the point after signal regeneration at which performance monitoring is or may be done. [After T1.105-1988]

The boundary that separates a network section from the adjacent circuit section, or separates an access circuit section from the adjacent DTE (data terminal equipment). Synonym boundary.