Microwave Journal

A Portable Rubidium Reference Timebase Generator

A rubidium reference timebase generator featuring a lightweight, portable configuration for use in the field at a reasonable cost

March 1, 1997

A Portable Rubidium Reference Timebase Generator

United Computer and Telecommunication Inc. (UCT)
Irvine, CA

With today's sophisticated communications systems comes the need for better frequency accuracy, control and correlation. Rubidium-based frequency and time standards have been the ultimate accurate signal source for laboratory use, but these instruments have not found general use in manufacturing or field-service applications due to their high cost and bulky size. A new rubidium-referenced timebase generator is available that brings this level of accuracy out of the lab and onto the test bench or into the field maintenance facility at a reasonable cost and in a lightweight, portable configuration.

The model UCT2008 rubidium reference timebase generator is a rugged, portable automatic frequency standard that provides frequency outputs based on a highly reliable internal rubidium oscillator. The generator provides five TTL outputs at 10, 5 and 1 MHz; 100 kHz; and 1 pps. The unit also provides eight 10 MHz sine-wave outputs. The generator features frequency accuracy of -11 at the time of shipment and 0.005 ppm over the instrument's lifetime. In addition, the UCT2008 is fully automatic and easy to use.

The UCT2008 meets the requirements of all of the wireless communications systems, including code-division and time-division multiple access, the Global System for Mobile communications and personal communications service systems without the need for periodic calibration. The new timebase generator can provide timing references easily for wireless communications systems and communications test equipment. Together with the UCT7000 frequency analyzer, the timebase generator can provide a complete frequency reference/analysis system.

The generator is capable of providing the master reference timebase for automatic test equipment (ATE) systems, supplying the frequency accuracy of an atomic clock to all the test equipment in the ATE rack. This multiple use reduces the overall ATE system cost, eliminating the need to purchase individual timebases for each piece of equipment in the system.

The UCT2008 can provide the reference frequency sources for production line equipment testing signal sources, signal generators, synthesizers and crystal oscillators, as well as frequency measurement equipment, spectrum analyzers and signal analyzers. Supplying multiple reference signals reduces test equipment cost and saves routine calibration cost and downtime.

The rubidium reference timebase generator also serves as a good master frequency reference source for engineering laboratory use, providing precision atomic reference frequencies to all measurement equipment in the lab. Using the UCT2008 to feed the equipment's external reference inputs improves its overall frequency accuracy to 0.00005 ppm. This improved accuracy reduces both development time and cost.

In addition to the instrument's -11 frequency accuracy, a Global Positioning Satellite option provides < 3 ×10-11 , -11 and -12 at 1, 10 and 100 s Allan variances, respectively. Figure 1 shows the unit's actual short-term stability. Figure 2 shows the long-term frequency aging and Figure 3 shows the Allan variance trend. Aging is -11 /month and -10 /year. The temperature coefficient is -10 over the range from -20° to +60°C.

Fig. 1: The timebase generator's short-term stability.

Fig. 2: The generator's long-term frequency aging trend.

Fig. 3: The Allan variance trend.

The timebase generator is housed in a rugged case that measures 8.8" × 3.5" × 12.7" without the handle, and weighs 10 lb. The unit operates from 115 or 230 V AC at 50 W maximum.

United Computer and Telecommunication Inc. (UCT)
Irvine, CA (714)833-0777.