Ken Mandelberg <km@mathcs.emory.edu> (05/24/91)
When my modem is connected to my phone line, I can hear a hum on
extension phones. The hum appears on extensions not connected to the
modem (as well as one that is connected through the modem). The hum
doesn't effect the modem at all, as far as I can tell.
Is there an isolating device I can put between the modem and phone
line that would isolate the modem (and hum) when the modem is not off
hook.
Ken Mandelberg | km@mathcs.emory.edu PREFERRED
Emory University | {rutgers,gatech}!emory!km UUCP
Dept of Math and CS | km@emory.bitnet NON-DOMAIN BITNET
Atlanta, GA 30322 | Phone: Voice (404) 727-7963, FAX 727-5611John Higdon <john@zygot.ati.com> (05/25/91)
Ken Mandelberg <km@mathcs.emory.edu> writes: > Is there an isolating device I can put between the modem and phone > line that would isolate the modem (and hum) when the modem is not off > hook. Any modem complying with Part 68 of the FCC R&R will not cause that problem. The hum is caused by an imbalance and/or leakage to ground within the modem. It should be repaired or replaced. Band-Aids should not be used in this case. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !
Julian Macassey <julian%bongo.UUCP@nosc.mil> (05/26/91)
In article <telecom11.394.2@eecs.nwu.edu> km@mathcs.emory.edu (Ken Mandelberg) writes: X-Telecom-Digest: Volume 11, Issue 394, Message 2 of 10 > When my modem is connected to my phone line, I can hear a hum on > extension phones. The hum appears on extensions not connected to the > modem (as well as one that is connected through the modem). The hum > doesn't effect the modem at all, as far as I can tell. > Is there an isolating device I can put between the modem and phone > line that would isolate the modem (and hum) when the modem is not off > hook. If you have hum on the line because of the modem, then there is something wrong with the modem, or the house wiring. You don't say what brand and model it is -- this is helpful when trouble shooting. But you can do one simple thing to decide whether it is a wiring problem. Locate a line cord with only two wires (most have four). Cheap nasty ones have two. Use that between the modem and see what happens to the hum. If it goes away, you can leave it that way. If you want to dig further, see if the modem has A-lead control (An option of Hayes and other modems). Remove the A-lead control. Check the jack the modem is connected to, wire only the red and green wires on the jack. If the hum persists, you have a "longtitudinal balance" problem with the modem. This means one side of the modem's phone line is too close to ground potential. It could be an internal short in the modem -- open and see. It could be a crummy cheap modem -- another reason to state brand and model. One way to fool the hum is switch the phone leads in the jack (The red and green ones), this often gets rid of hum. Also in gross cases, you may have the jack wired with a ground wire (usually yellow) where Tip or Ring should be. Anyhow if the modem meets FCC Part 68 and the phone wiring is Kosher, you should have no hum. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian 742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice (213) 653-4495