The United States of America As Represented by the Administrator of the

Other

Victor S Reinhardt

William A Adams

Robert A Frosch

Peter O Cervenka

Lou F Kalil

A thermal probe (10) for averaging temperature fluctuations over a prolonged period is formed with a temperature sensor (22) embedded inside a solid object (12) of a thermally conducting material. The solid object is held in a position equidistantly spaced apart from the interior surfaces of a closed housing (16) by a mount (14) made of a thermally insulating material. The housing is sealed to trap a vacuum or mass of air inside and thereby prevent transfer of heat directly between the environment outside of the housing and the solid object. Electrical leads (24) couple the temperature sensor with a connector (26) on the outside of the housing. Other solid objects of different sizes and materials may be substituted for the cylindrically-shaped object to vary the time constant of the probe.

Temperature averaging thermal probe

A low noise RF signal phase comparator comprised of two high stability driver-buffer amplifiers (16 and 18) driving a double balanced mixer (14) which operate to generate a beat frequency between the two RF input signals coupled to the amplifiers from the RF sources. The beat frequency output from the mixer is applied to a low noise zero crossing detector (20) which generates a square wave output whose positive and negative going edges provide a measure of the phase difference between the two RF inputs. Temperature stability is provided by mounting the amplifiers (16 and 18) and mixer (14) on a common circuit board (29) with the active circuit elements (62, 68, 70, 82, 88, 90, 110) thereof being located on one side of a circuit board (29) while the passive circuit elements (112) are located on the opposite side. A common heat sink (28) consisting of a relatively thick metal plate of relatively large mass and having a plurality of recesses or bores (31, 33, 35, 37, 39, 41) formed therein is located adjacent the circuit board (29) such that the active circuit elements (62, 68, 70, 82, 88, 90, 110) are embedded into the bores which has the effect of slowing down the effect of ambient temperature changes and reduces the temperature gradients between the active circuit elements, and thus improving the cancellation of temperature effects inherent in such devices. Additionally, the two amplifiers (16 and 18) include individual voltage regulators (70 and 90) which effectively increases RF isolation by reducing cross-talk through the power supply connected thereto.

High stability buffered phase comparator

An electrical RF signal amplifier for providing high temperature stability and RF isolation and comprised of an integrated circuit voltage regulator (26), a single transistor (22), and an integrated circuit operational amplifier (24) mounted on a circuit board (80) such that passive circuit elements (92) are located on side of the circuit board while the active circuit elements (22, 24, 26) are located on the other side. The active circuit elements are embedded in a common heat sink (70) so that a common temperature reference is provided for changes in ambient temperature. The single transistor (22) and operational amplifier (24) are connected together to form a feedback amplifier powered from the voltage regulator (26) with transistor (22) implementing primarily the desired signal gain while the operational amplifier (24) implements signal isolation. Further RF isolation is provided by the voltage regulator (26) which inhibits cross-talk from other like amplifiers powered from a common power supply. Input and output terminals consisting of coaxial connectors (44, 26) are located on the sides of a housing (69) in which all the circuit components and heat sink (80) are located.

High stability amplifier

A maser functioning as a frequency standard stable to one part in 10.sup.14 includes a variable volume, constant surface area storage bulb having a fixed volume portion located in a resonant cavity from which the frequency standard is derived. A variable volume portion of the bulb, exterior to the resonant cavity, has a maximum volume on the same order of magnitude as the fixed volume bulb portion. The cavity has a length to radius ratio of at least 3:1 so that the operation is attained without the need for a feedback loop. A baffle plate, between the fixed and variable volume bulb portions, includes apertures for enabling hydrogen atoms to pass between the two bulb portions and is an electromagnetic shield that prevents coupling of the electromagnetic field of the cavity into the variable volume bulb portion. The maser is operated so that the zero wall shift frequency thereof can be determined by being operated at first and second very accurately controlled temperatures for identical small and large volumes. From the two temperatures and volumes, the zero wall shift frequency is determined as the intersection of two straight lines.

External bulb variable volume maser

The phase and/or period stability of a device being tested is determined by connecting the device in one orthogonal arm of a phase detector having a mixer. In the other arm is an adjustable, variable phase shift device, such as a line stretcher. The output of the mixer is fed through an active low pass filter to derive a DC voltage indicative of the phase shift of the tested device. Initially, the variable phase device is adjusted so that the DC voltage is approximately zero to nullify the phase shift of the tested device under normal conditions. The DC voltage level is converted into a time interval indicative of the phase change of the tested device by determining when the level equals the amplitude of a low frequency ramp voltage that functions similar to a beat frequency output of a prior art dual mixer detector. The interval between adjacent equality points for the phase indicating voltage and the ramp voltage can be measured or the period between a reference point on the ramp voltage and the equality between the ramp voltage and the phase indicating voltage can be measured.

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Gaithersburg, MD, United States of America

Victor S Reinhardt