Delay Line Structure And Design - Colby Instruments PDL-100A Operating And Programming Manual

Chapter 1

1.0.2 Delay Line Structure and Design

The PDL Series of delay line instruments is based on an "electromechanical
trombone" or moveable delay line. A high frequency signal passing through an
expanded or contracted trombone experiences correspondingly more or less
electrical delay. The trombone tubes consist of four flexible lines connected in
series to achieve a total delay of 625 ps or 312.5 ps if used individually as a set of
two. The trombone delay lines are exposed at the instrument front panel to allow
access to each delay line pair. All PDL-100A Series instruments include a semi-
rigid coaxial cable connecting the top pair in series to the bottom pair.
A high torque aerospace-grade high precision stepper motor with a custom
precision lead screw is used to position a sled on which one part of the trombone
tubing is attached. The PDL-100A's precision interfaces are designed to
minimize impedance mismatches while a proprietary contact design achieves
reliability while minimizing any signal loss or noise.
An embedded CPU microcontroller reads commands from either a Microterminal
(numeric keypad with LCD display) or from GPIB (IEEE488.2), TCP/IP
(Winsock), or RS-232 Serial Port interfaces. Commands are processed to move
the stepper motor in high-resolution step increments to as fine as 0.50
picoseconds as measured across the series path of two trombone pairs (top and
bottom). This is the Series Connected configuration. Removing a vertical coaxial
cable on the front panel allows increased precision to 0.25 picoseconds as
measured across only one trombone pair (top or bottom). This is the Parallel
Connected configuration.
If required (as in PDL-100A-1.25NS and above), semi-rigid coaxial cable and
low-loss microwave relay sections are also turned on or off (to add or remove
delay) into the signal path to extend the total delay range of each instrument.
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Description of the PDL-100A Programmable Delay Line Series
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