It doesn't take much in the way of frequency for interconnects to take on transmission-line characteristics.
Unless you work with DC only, you'll have to deal with transmission lines in some way. Everything is a transmission line, depending on signal frequency.
Today, we tend to associate transmission lines with multi-gigabit data links, but transmission lines appear even at low speeds. That's what engineers dealt with in 1998, when kilobit modems were what we used. This week's quiz comes from "Rules tell whether interconnections act like transmission lines," part one of "Designers Guide to transmission lines and interconnections" by David Royle. This part was published in the June 23, 1988 issue of EDN. The article opened with four quiz questions, which I've turned into five. Because the original questions were open ended, I've adapted them to fit the multiple-choice format.
For each answer, I've included Royle's explanations, which are quite lengthy and same have their own figures or repeat figures from the questions. Because the explanations are so long, I've broken with tradition and put explanations across the last four pages. The answers and explanations for Questions 1 and 2 appear on page 6 with the remaining explanations on pages 7 to 9.
Not only do you get extra credit for reading them all, but there's special bonus on the last page.
1. The physical layer for a local-area network consists of 19.2 kbaud/s modems interconnected as shown below. The carrier frequency is 200 kHz,; 50 Ω RG-22 coaxial cable connects the modems. What is the maximum interconnection length that you can use?
- 10 Ft.
- 3 m
- 10 m
- 24 ft.
- 50 ft.
- 20 m
- 24 m
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