bnelson@CCB.BBN.COM.UUCP (03/24/87)
It may have been fun to watch the guys trace your loop fault, but it's really a lot of hard work to do it correctly. The buzzer was most likely the signal source on either a pair or on a single wire (and ground) and the probe was an inductive amplifier which is used to magnetically couple to the suspected 'good' wires. Where the signal stops, the line is broken, not unlike signal tracing in RF troubleshooting work. By sweeping the antenna of the amplifier near the cable containing your wire(s) they can listen for the distinctive 'tweedle' of the buzzer picked up from the magnetic emanations of the electrical signal. What's really bad is trying to do this while someone else in the same building is doing the same thing! The butt set only helps to amplify the signal a bit. Many units come with the tiny speaker built right into the end of the probe. This method is only a half-step up from a light bulb and a battery. Many more sophisticated methods (obviously) exist, such as TDRM (time-domain reflectrometry) which measures the impedence steps using various standing waves and can detect opens, shorts, splits, some types of bugs, connectors, etc. within a few feet. The sky is the limit (pun) on telco diagnostic equipment these days. "This document contains statements of opinion by the author which are not attributable to BBN Communications Corporation or its management." Barry C. Nelson / BBNCC Product Management/International Certifications