ccohesh@ucdavis.UUCP (Hesh) (08/08/85)
[]
my roomate recently bought a special 2-line phone; it
seems to be causing problems with my modem. when this
phone is hooked up, i receive voluminous amounts of your
standard modem type garbage ("{i", "|}", etc.). i'm
convinced that this phone is the cause, because by simply
disconnecting it the garbage stops.
has anybody else experienced this? what exactly is causing this?
is there a solution which doesn't include tossing this phone?
--
-- Hesh
-- ucdavis!ccohesh.BERKELEY.EDU (ARPA)
-- {...}!ucbvax!ucdavis!ccohesh (UUCP)mark@cbosgd.UUCP (Mark Horton) (08/09/85)
In article <427@ucdavis.UUCP> ccohesh@ucdavis.UUCP (Hesh) writes: >my roomate recently bought a special 2-line phone; it >seems to be causing problems with my modem. when this >phone is hooked up, i receive voluminous amounts of your >standard modem type garbage ("{i", "|}", etc.). You didn't say what kind of modem or what kind of phone. However, a 2 line phone ought to be just a switch and a phone; if you don't have your phone picked up on the modem line it shouldn't do anything to your line. You might try making sure only the modem line pair gets to the modem. I've installed modems through RJ-11 jacks and found that the second (supposedly unused) pair gets an incredible hum put onto it by the modem. That is, I have a voice line and a data line and RJ14 jacks (e.g. regular modular jacks where the other line gets put onto the two extra pins.) Some wall jacks have the voice line in the primary slot, some the modem line. I plug the modem into a modem jack and suddenly there's a big hum on the voice line. Never could figure out why. I think this has happened with several different modems. The fix is to get one of these plugs with 3 outputs - line 1, line 2, and both, and plug your modem into a "line 1" jack, which disconnects the line 2 leads. Or do a little wiring to get the same effect. Of course, it goes without saying that if you pick up the phone on your modem line while you have a data call in progress, it will put noise on the line. Mark
dsi@unccvax.UUCP (Dataspan Inc) (08/10/85)
This might be a case of the AML/SSL(?) device giving a lot of problems.
These units look like a very large lid for ladies' powder, coloured the
obligatory telephone grey, and are screwed to the wall near the telephone
in question. What this little turkey does (evidently) is multiplex a second
telephone circuit on the present subscriber loop. There is also a trap
which notches out the various carriers, etc. to control the AML unit -
for the regular lines on the ** other ** loop.
AML units are not noted for their tremendous linearity and distortion
characteristics. In addition, they have a on-board battery (charged by the
-48 v from the CO) which runs down after about an hour of talking. If
some turkey keeps ringing your phone while you are away, you get a dead
battery in about 5 minutes. ( Even if your modem did work through it, the
AML signal quality deteriorates rapidly because of this....)
You can't (fer sure) use a UDS 9600 A/B over one of the Continental
Telephone AML's; but the outside trap for the host line doesn't seem to
affect this modem. However, most yuppie modems don't have automatic adaptive
equalisation, and might get screwed up by the group delay characteristics
of this filter (it didn't have to be linear phase for the original purpose).
Try the other telephone line, and look for an AML unit near one
of your telephones; or a trap (it is usually stamped with the Continental
Telephone logo) near the loop arc suppressor outside. If you have to get
rid of an AML and insist on a real dry pair, DO NOT TELL THEM IT IS FOR DATA
but rather that you are a doctor (or something) and need more reliable
communications...the battery running down is a real inconvenience.
See, your phones must have some frequency response past 3 kHz.....
David Anthony
DataSpan, Incsmb@ulysses.UUCP (Steven Bellovin) (08/10/85)
> In article <427@ucdavis.UUCP> ccohesh@ucdavis.UUCP (Hesh) writes: > >my roomate recently bought a special 2-line phone; it > >seems to be causing problems with my modem. when this > >phone is hooked up, i receive voluminous amounts of your > >standard modem type garbage ("{i", "|}", etc.). > > You didn't say what kind of modem or what kind of phone. > However, a 2 line phone ought to be just a switch and a phone; > if you don't have your phone picked up on the modem line it > shouldn't do anything to your line. For most phones, when they are on-hook, there's ring-detector cirucitry active. Depending on the design of the phone -- I doubt that the problem is because the new phone is 2-line. > You might try making sure only the modem line pair gets to the > modem. I've installed modems through RJ-11 jacks and found that > the second (supposedly unused) pair gets an incredible hum put > onto it by the modem. That is, I have a voice line and a data > line and RJ14 jacks (e.g. regular modular jacks where the other > line gets put onto the two extra pins.) Some wall jacks have > the voice line in the primary slot, some the modem line. I plug > the modem into a modem jack and suddenly there's a big hum on the > voice line. Never could figure out why. I think this has happened > with several different modems. The fix is to get one of these plugs > with 3 outputs - line 1, line 2, and both, and plug your modem into > a "line 1" jack, which disconnects the line 2 leads. Or do a little > wiring to get the same effect. Many modems provide A-A1 signalling on the other two lines, for use with office key systems.
larry@kitty.UUCP (Larry Lippman) (08/11/85)
> my roomate recently bought a special 2-line phone; it > seems to be causing problems with my modem. when this > phone is hooked up, i receive voluminous amounts of your > standard modem type garbage ("{i", "|}", etc.). i'm > convinced that this phone is the cause, because by simply > disconnecting it the garbage stops. > > has anybody else experienced this? what exactly is causing this? > is there a solution which doesn't include tossing this phone? If I had a dollar for every model of electronic single and two-line telephone presently on the market, I'd be a millionaire... Since I don't know the specific telephone you are having trouble with, I will take a guess at the problem based upon past experience. Some of the 'fancier' electronic telephones having built-in dialers, call timers, etc. are self-powered from the telephone line; i.e., in an on-hook condition they 'steal' several mA of current from the telephone line to power a DC/DC converter which in turn charges a small nicad battery. This provides a continuous source of power for the telephone electronics. The DC/DC converter could be generating high frequency noise which is being transmitted back over the telephone line and hence into your modem. Another possibility is that even if the telephone is not telephone line-powered but uses an AC transformer, there may be RFI imposed on the telephone line due to shoddy microprocessor design (many of these telephones use a single-chip microprocessor to support the various features). As far as a solution is concerned - I don't have one. About the only possibility would be to build a low-pass filter for use in between the offending telephone and telephone line. That would be a rather tricky thing to do, since there would be substantial constraints on such a circuit design so as not to impair the normal telephone operation. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | Larry Lippman @ Recognition Research Corp., Clarence, New York | | UUCP {decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry | | {rice,shell}!baylor!/ | | VOICE 716/741-9185 syr!buf!/ | | TELEX {via WUI} 69-71461 ansbak: ELGECOMCLR | | | | "Have you hugged your cat today?" | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++