That portion of the ionosphere existing approximately 50 to 95 km above the surface of the Earth.
Note: Attenuation of radio waves, caused by ionospheric free-electron density generated by solar radiation, is pronounced during daylight hours. Because solar radiation is not present at night, ionization ceases, and hence attenuation of radio waves ceases.

(Pronounced "D-Star") See specific detectivity.

A framing standard for traditional time-division multiplexing, which standard describes user channels multiplexed onto a trunk that has been segmented (framed) into 24 bytes of 8 bits each.
Note: The multiplexing function is performed in the D-4 framing structure by interleaving bits of consecutive bytes as they are presented from individual circuits into each D-4 frame.

Abbreviation for digital-to-analog. See digital transmission system.

Synonym specific detectivity.

A patch bay designed for patching and monitoring of unbalanced data circuits at rates up to 1 Mb/s.

See channel bank.

See channel bank.

See channel bank.

See channel bank.