Scan Loss And Its Elimination In CATV Swept Frequency Measurements (1973)

By Bob Cowart, Gill Cable & Russell D. Anderson, Avantek, Inc

This is a tutorial article on Scan Loss. Good construction and maintenance practices in conjunction with FCC and DOC specifications have emphasized the need for increased swept frequency measurements. Swept frequency measurements to determine: return loss, component isolation, flatness, spurious responses, probable causes of group delay as well as bench alignment and preinstallation checkout of passive or active system components.

Unfortunately, the possibility of amplitude error does exist especially in the case of severe amplitude changes (dB/MHzl through the mechanism of Scan Loss.

Please note the following photos of the swept response of a 0-300 MHz spectrum -- in which a Jerrold TLB-2 trap is inserted. Using a standard sweeper with variable sweep speed, an H-P 84 71A detector, 3 feet of RG 58/u cable, and a storage oscilloscope calibrated 30 MHz per devision, two photos were made.

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