Design Of Signal Generator Research Articles

HF and VHF Source Stabilization Technique Incorporating Q-Multiplied Quartz Crystal Resonator

A new approach is described for the desiga of HF/VHF crystal-controlled frequency sources exhibiting theoretical short-term stability unattainable through the use of conventional quartz oscillator design. The signal generator design uses the concept of AFC stabilization of a conventional quartz oscillator (VCXO) by means of a crystal-controlled highly selective active frequency reference. The AFC reference is a phase-shift type frequency discriminator that employs a product detector and an active Q-multiplied quartz crystal resonator. The extremely selective transmission response, large group delay, and power gain exhibited by the resonator, together with resonator phase noise levels comparable to that exhibited by the oscillator-maintaining circuit, provide the principal means for prediction of superior output signal spectral purity. Models of the resonators have been designed and constructed at 30 and 80 MHz, exhibiting 3-dB bandwidths of 30 and 160 Hz, respectively. Based on actual measurement of VHF Q-multiplied crystal resonator performance characteristics, approximately 16 dB improvement in VHF crystal-controlled frequency source spectral purity at low and moderate modulation rates is possible, compared to that attainable using the best available VHF quartz oscillator circuit designs.

A systems approach to signal generation

A modular approach to signal-generator design means that r.f. test systems can easily be changed to meet different requirements, and difficult applications no longer require the purchase of expensive systems with a great deal of redundancy.

The design of signal generators at centimetre wavelengths

The design of signal generators at centimetre wavelengths

The design of signal generators for the measurement of receiver noise factor at 10- and 3-cm wavelengths

The design of signal generators for the measurement of receiver noise factors at 10- and 3-cm wavelengths is described, one of the main points being the elimination of connectors which give unreproducible results. To achieve this, the monitor and attenuator are made integral parts of the signal generator; the signal emerges through a length of Pyrotenax cable of over 10 db attenuation, giving a resistive output. The signal generator is calibrated by measurement of the power output when the piston attenuator is set to low attenuation but still obeys the theoretical law. Known power outputs of the order of 10 -14 W may thus be obtained with an accuracy of ± 1 db. The screening is such that no leakage can be detected with the most sensitive receivers.

The design of signal generators for centimetre wavelengths

The function of a signal generator is to provide a test signal of known frequency and amplitude. In the design of such instruments for centimetre wavelengths, problems chiefly associated with the determination of the signal amplitude have necessitated some departure from conventional practice at lower frequencies. The main difficulties encountered have been in the design of a suitable output attenuator, together with a monitor by which the output may be maintained constant at some reference level, and the provision of adequate screening for the generator. This paper seeks to acquaint the reader with some of the methods that have been evolved to meet these problems, and includes a brief description of a typical signal generator operating in the 6-cm wavelength region.The paper is not intended to be a complete survey of the work which has been carried out on this subject during the war, but it is hoped that it will be of value in indicating some of the lines along which development has taken place.