larry@uunet.uu.net (Larry Lippman) (04/03/91)
In article <telecom11.260.4@eecs.nwu.edu> DISC3C1@jetson.uh.edu writes: > Who needs to buy one of these things? There are numbers you can call, > that are supposed to show you if your line is been tapped. Oh, right. Like 1-800-FIND-BUG or 1-900-FIND-TAP. :-) > They call it a sweep. It is an alternating pitch supposedly; and > is meant to stay high pitched if your line is being bugged and > alternate if not. For example, call this sweep: 214-357-8686 I think someone has been watching too many James Bond movies. While I had a pretty good suspicion as to what the above number actually is, I called it to make certain. It sounds to me like a 24B Loop Checker circuit. These "sweep tone" lines, which exist in many, but by no means all central offices, are used by installers to make a rapid assessment of the transmission quality of subscriber loops. Dialing the number associated with the test line connects it to a loop checker generator circuit which places a continuously repeating sweep tone on the line. The sweep time period is usually 15 to 20 seconds. In the field, an installer uses a simple audio frequency level meter with a specially calibrated scale (it usually has red and green colored regions for "go" and "no-go"). The installer watches the meter while listening to the sweep tone; if the needle states in the green, then the loop transmission quality is usually "okay". The above system is usually called a "Loop Checker". From a transmission measurement standpoint, it provides rather imprecise information. However, it is a quick and dirty measurement method which requires inexpensive field equipment and does not require much training on the part of the installer for use. It is important to realize that the amplitude of such loop checker generator lines is NOT CONSTANT over the swept frequency range. Therefore, this line is of no value for serious transmission measurements. The expected amplitude variation is taken into consideration on the level meter indicator scale. Needless to say, loop checker test lines have *NO* utility in the detection and location of eavesdropping devices on a telephone line. > [Moderator's Note: Where did you get your information from, Scott? The human imagination has no bounds, eh? :-) Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry
"a.e.mossberg" <aem@mthvax.cs.miami.edu> (04/07/91)
In <telecom11.268.1@eecs.nwu.edu> kitty!larry@uunet.uu.net (Larry Lippman) writes: > Needless to say, loop checker test lines have *NO* utility in the > detection and location of eavesdropping devices on a telephone >line. > The human imagination has no bounds, eh? :-) One time someone told me, in the strictest confidence, if I swore not to reveal the number to anyone else, that they would give me a number that I could call and it would let me know if my line was tapped. Well, I was very dubious and had a strong suspicion what it would turn out to be, but played along anyway. "Okay, here it is. Now you call and if it cycles through a bunch of frequencies your line is okay, but if the number is busy, that means your line is tapped!" This person, in Miami, had regularly been calling this number in California to check his line. No, I didn't call it, and no, I didn't tell him he was an idiot. aem@mthvax.cs.miami.edu