DECUS Decade Divider Module

Contents

PRODUCT INDEX

• Introduction
• Features and Specifications
• Physical
• Outputs
• Design, Operation and Test
• Design
• Operation
• Test
• Input
• Outputs
• Power
• Polarity
• Connections
• Voltage
• Current
• Dissipation
• Parts List
• Revision Summary

Page 2

Introduction

The following describes the design, construction, operation and use of the DECUS divider module. Photo 2 shows a top view of the module and Photo 3 shows the bottom. The primary use of the module is to condition the 10 megahertz (MHz) signal from a rubidium oscillator such as the LPRO-101 or FRS-C units manufactured by EFRATOM Ball, Inc. The DECUS module divides the 10 MHz output from these units to produce marker signals at various frequencies.

The DECUS module also provides buffered 10 MHz outputs that can be used to distribute the conditoned signal to test equipment.

If you require a multiplied frequency output in addition to the decade divisor, you may be interested in the DECL module. If you have a FE-5680 rubidium reference, you may be interested in the FEBO module.

The module's conditioning circuit and divider chip can also be used for other applications requiring signal conditioning and dividing, but this usage is outside the scope of this document.

Page 3

Features and Specifications

For the following, refer to the DECUS schematic titled "DECUS DIVIDER BOARD FOR LPRO-10 and FRS-C RUBIDIUM SOURCES."

You can download the DECUS schematic as a zip file.

The schematic shows the components, circuitry and some operational restrictions for the module. The Parts List provides additional information about the components used to assemble the module.

As shown in photo 2, the module measures approximately 1 1/4 by 7/8 inches (32 by 23 mm). Signal connections are provided on two 12-pin single row pin headers. The header connections are labeled "A" to "X" for easy reference. Header pins are spaced one tenth of an inch apart and the header rows are spaced 0.6 inch apart. This allows the module to be used with in-line sockets or wired directly to a protoboard.

The module provides nine different divider outputs, ranging from one Hertz to one megahertz. The module also provides three ten megahertz buffered outputs for driving time base inputs of test equipment. Two buffer gates are uncommitted to allow any two of the outputs to be buffered or to allow buffering of an external signal (e.g., a lock indicator for an LPRO or FRS output).

Divider outputs are driven by microprocessor port pins capable of sourcing or sinking up to 100 milliamperes each. The one Hertz output can directly drive an LED to act as an "active" indicator. These drive capabilities are limited by the choice of input voltage and the current limitations of the regulator, as noted in the Power section.

Page 4

Design, Operation and Test

To set up the module for operation, it is necessary only to supply it with power and an input signal. Once set up for operation, outputs are continuously available at the lettered output pins, as indicated on the schematic (also see the PIN/PORT MAPPING table on the schematic).

The following sections describe power and signal requirements, module connections and test procedures.

Photo 3 shows the front panel of the DECUS test fixture and Photo 4 shows the back of the DECUS test fixture.

Page 5

Input

The input signal is applied between the module pins labeled "K" and "L" (ground), as shown in the schematic. The conditioning circuit is designed to be compatible with the LPRO-101 specifications with a typical input signal of 0.55 Volts RMS (approximately 1.5 Volts peak to peak). DECUS Photo 1 shows the typical input conditioning signals for a LPRO input.

Note: The input may not operate reliably for signal inputs under one Volt peak to peak. Inputs as high as 6 Volts peak to peak have been used but are not recommended for routine operation.

To verify the correct operation of the conditioning circuit, use an oscilloscope to observe the input signal between ground and pin 1 of the hex inverter. If the input voltage is within the range specified above, a 10 MHz square wave can be observed at pins "H", "T" and "V." Buffered versions of the conditioned signal appear at pins "J", "O" and "P" as shown in the schematic.

Page 6

Outputs

The DECUS output frequencies and module pins are:

The above data and microprocessor port/pin mapping also appears on the schematic in the PIN/PORT MAPPING table.

Page 7

Power

The module is not protected against input voltage reversal. Take care to verify that the correct voltage polarity is applied to the power input pins.

The zener can be wired into the circuit by removing the shorting jumper across the zener on the bottom of the module (also see the schematic). When using the zener, the input voltage applied to the module should be a minimum of 15 Volts. For direct operation at lower voltages, such as 5 Volts, the shorting jumper should be left in place (the factory-wired default).

To use the zener diode, cut the shorting jumper across the diode on the bottom side of the board. The addition of the zener drops the regulator input voltage to approximately 15 Volts. Note that operating the module at higher input voltages (e.g., above 10 Volts) may significantly limit divider output currents, as noted below.

Once the proper input voltage has been selected, configured and applied to pin "M", the operation of the regulator can be verified by measuring the voltage betweeen ground and the power pins of the ICs. For example, 3.3 Volts should appear on pin 14 of the hex inverter and on pin 7 of the microprocessor. The measured voltage should be within a tenth of a Volt of 3.3 Volts. If the regulator is hot or the output voltage is not within specification, it is likely that the input voltage is too high or too low.

Page 8

Revision Summary