This paper describes the accomplishments of a program performed at EG&G to greatly reduce the warm-up time for a rubidium frequency standard (RFS) from minutes to seconds. Typical warm-up times for an RFS range from 1.5 to 10 minutes at room temperature. In some tactical situations, such warm-up times, which may be increased by low ambient temperatures, are undesirable or unacceptable, requiring for example that the RFS be turned on first when setting up a station or be kept "hot" while other equipment is off to conserve power. This program focused on the physics package. The areas that were investigated and improved related to warm-up of the absorption cell (using a design with sapphire faceplates), lighting and warm-up of the rubidium lamp, and servo acquisition and lock. In the final configuration lock was achieved in 7 seconds at +5 "C. The modifications made were for engineering evaluation. Additional development is needed before a practical ultrafast warm-up rubidium reference can be produced. DESCRIPTION OF BASELINE RUBIDIUM FREQUENCY STANDARDThe baseline design for this effort was the EG&G RFS-10-7 Rubidium Frequency Standard, a standard military unit. The physics package assembly and parts are shown in Figure 1, and the cross section is shown in Figure 5. A comprehensive discussion of rubidium frequency standards is given in Ref I .A rubidium frequency standard is basically a crystal oscillator locked to an atomic reference (the rubidium physics package and supporting electronics) which serves as a passive discriminator, producing an error signal that varies in magnitude and sense as a function of the difference in frequency between the applied rf excitation, derived from the crystal oscillator, and the atomic resonance. The rubidium frequency is about 6835 MHz, and a line Q of IO' is typical. The error signal is a result of audio frequency FM applied to the microwave excitation, which causes variations in the transmission of light through the resonance or absorption cell. A photodetector senses this response.Physics package operation is supported by an exciter for the rubidium lamp and temperature controllers for the lamp and cell ovens. The error signal is processed by a servoamplifier, which generates a voltage that controls the frequency of the crystal oscillator. This oscillator produces the user output and also, via a synthesizer and multiplier chain, drives the microwave cavity . The overall scheme is that of a frequency lock loop.The RFS-10-7 resonance cavity contains a filter cell and a separate absorption cell (Ref. 3). This arrangement generally gives better performance as an atomic frequency standard (or clock) than if the two functions are performed by a single integrated cell.
A S A REPRESENTATIVE of the Rome Air Development Center, I would like to personally join our co-sponsor, the Armour Research Foundation, in welcoming you to this symposium in the field of reliability physics. This symposium enjoys the distinction, I believe, of being the first in this important aspect of the general subject of reliability, and since I am sure it is destined to play a very fundamental role in that subject, it will probably not be the last. Since the majority of the papers to be presented here will describe work which was largely sponsored by the Rome Air Development Center, it was felt not only appropriate, but helpful, to relate to you, at the very outset, something of the origins and the goals of the Physics of Failure program at RADC.The Rome Air Development Center has been active in the field of reliability for the past eight years, particularly as applied to the development of ground based electronics eqtuipment for the Air Force. The equipment we develop is used to acquire, process, transmit, and present data for use in Air Force Command and Control Systems. I would like, first, to describe briefly some of our problems in reliability and then show how they pointed up the need for a new approach.The principal motivation for early reliability design and engineering came, initially, from the military services. It arose from a situation which, unfortunately, is still with us today-military equipment which keeps growing more complex and, as a consequence, failing more often.The requirements and environments for ground electronic equipment are, in many respects, less severe than those for airborne or missile electronics equipment. For example, size and weight, operation at high temperatures, and extreme shock and vibration are far less critical requirements on the ground than for airborne or missile applications. There are two factors, however, which have tended to increase the problems confronting the designer of ground electronic equipment: (1) an increasing number of functions previously performed by airborne electronic devices must now be designed into the ground equipment, and(2) as the speeds and altitudes of aircraft and missiles increase, a 4 i;X
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