Agilent 1964-02 free download

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HEWLETT-PACKARD JOURNAL T E C H N I C A L I N F O R M A T I O N F R O M T H E - h p . L A B O R A T O R I E S Vol. 15, No. ' LISHED CALIFORNIA THE HEWLETT-PACKARD COMPANY, 1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA FEBRUARY, 1964 Time Domain Reflectometry J. HE MEASUREMENTS we make are limited by the tools we have at our disposal. Often measurements must be made by roundabout methods because no instruments exist with which to make them directly. Such difficul ties are typical of pioneering work in any field. It is then the business of the instrument maker to devise tools to simplify frequent measuring needs. Sometimes the cumbersome methods first required SYSTEM UNDER TEST become so habitual, so ingrained, that the development of improved techniques is overlooked. This seems to Fig. 2. A Typical Time Domain Reflectometer. be the case with respect to transmission and reflection measurement in the UHF and microwave range. Meth ods long in use here are now obsolete but are slow to pletely new set of data must be taken and re-inter preted. The process is very time-consuming. give way to more modern direct methods. The time-honored method of measuring reflections The swept-frequency reflectometer speeds the meas on a transmission line is to measure, as a function of urement considerably but does nothing to simplify the task of interpretation. Since no phase information is frequency, the standing wave ratio (SWR) produced obtained, the results from even a single simple discon by the reflections. The resulting curves of magnitude tinuity are ambiguous. and phase of the SWR can, in simple cases, be un scrambled to give the location and nature of the reflec The direct method of measuring reflections is to tions, but the interpretation is difficult at best. With send out a pulse and listen for the echoes. This is what each alteration or attempted improvement, a corn- we do in radar, this is what the do