Abstract: A digital apparatus for performing minimum-shift-keying (MSK) modulation includes an oscillatory circuit which provides two frequencies related in a predetermined manner, and also includes a processing circuit which divides a stream of digital data to be transmitted into two parallel substreams, one substream comprising even numbered bits from the serial stream and the other substream comprising odd numbered bits from the serial stream. A combining circuit selects one of the frequencies provided by the oscillatory circuit according to the equivalence or divergence of the states of the digital substreams, and further provides as an output the selected frequency waveform or its inverse according to the state of one of the substreams.

Abstract: A reliable, repeatable and stable VLF/LF atmospheric noise generator is cble of producing noise with known or given amplitude probability distributions and temporal characteristics such as pulse duration, pulse spacing, pulses per unit time and the discharge fine structure between pulses. A pseudo random noise carrier signal is multiplied in a plurality of digital-to-analog converters with the discharge envelopes created in a plurality of interconnected discharge envelope generators. The discharges are representative of cloud-to-ground discharges, intercloud discharges, the discharge rate, strokes per discharge and the discharge fine structure. All of the discharges are readily modifiable by suitably reprogramming operatively coupled memories and microprocessors in accordance with selected loading instructions.