Abstract: A synthesizer is disclosed having a frequency modulation phase-locked loop incorporating a voltage controlled oscillator (VCO) producing a 100 MHz, say, carrier which can be frequency-modulated. The VCO output is combined in a mixer with the output of another VCO which is variable stepwise. A frequency divider with a division factor of, say, 10, can be selectively interposed in the output of the VCO by means of a switch, and the resultant divided output is summed with a fixed frequency of, say, 90 MHz so as bring the output back to the 100 MHz carrier frequency. In this way, not only is the FM reduced by a factor of 10 (in this example) but so is the noise.

Abstract: A microprocessor-controlled synthesizer has a low frequency section producing a first output frequency and a comb loop producing a second output frequency. The comb loop includes a multiplier which produces harmonics of 100 MHz one of which is selected and fed to a mixer in a phase-locked loop having a variable divider, the other input of the mixer being a VCO output frequency. At low values of the second output frequency, the phase detector locks to the difference output from the mixer, at higher values to the sum output. The output from the mixer is mixed in a second mixer with the output of a further VCO, and a second phase detector selects the sum output from the second mixer to cover the first half of each decade of MHz and selects the difference output to cover the second half of the decade.

Abstract: Electrical noise is suppressed on an input signal by squaring the input signal and any noise thereon, removing the sinusoidal terms in the squared output (as by averaging), subtracting the d.c. noise component, and taking the square root of the remainder, so as to produce an r.m.s. dependent, substantially noise free output. If desired, the noise suppression circuitry may be combined in a low signal measuring instrument in which the input signal is repetitively sampled and freed of noise in the manner described, the output then being measured on a d.c. meter.

Abstract: An electrical signal generator for generating signals at specific frequencies includes means for producing an adjustable frequency output, adjusting means for causing changes in the output frequency, and control means for adjustably pre-selecting the sizes of the frequency changes. In this way, the operator can be provided with a frequency changing control which, when operated, causes the output frequency to change in predetermined steps.