Abstract: A waveform generator suitable for use in the testing of instrument landing systems comprising: a first generator (1) for generating digitally a first waveform comprising the superposition of a second waveform (19) of a first frequency and a third waveform (21) of a second frequency; a second generator (3) for generating digitally a fourth waveform comprising the superposition of a fifth waveform (25 or 27) comprising a phase reversed version of one (19 or 21) of said second (19) and third (21) waveforms of the frequency of said one waveform (19 or 21) and a sixth waveform (23 or 29) in phase with and of the frequency of the other one (19 or 21) of said second (19) and third (21) waveforms; and a circuit (7) for combining said first and fourth waveforms thereby to produce a waveform suitable for said use.

Abstract: A direct digital synthesizer of the phase-accumulator type, constructed entirely of binary-radix digital hardware, generates signals with decimally-defined frequency resolution. The synthesizer is supplied with a clock signal which is also decimally-defined. The usual decimal-binary incompatibility problems of such a combination are overcome by the use of a phase accumulator which is partitioned into two segments. The first segment is assigned the most significant portion of the desired frequency, and the other segment is assigned the remaining portion of the desired frequency. The two segments have different arithmetic moduli. Typically, the modulus of the first segment is a power of two, while that of the second segment is an integer other than a power of two. A procedure is given for determining both the point of partition and the second arithmetic modulus.