Path: utzoo!telecom-request Date: Thu, 11 Apr 91 06:08:26 GMT From: Mark Cheeseman Newsgroups: comp.dcom.telecom Subject: Re: Halogen Lamp Interfering With Cordless Message-ID: Organization: RUNX Un*x Timeshare. Sydney, Australia. Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 288, Message 3 of 13 Lines: 34 In article , slcpi!admin8779.shearson. com!mjohnsto@uunet.uu.net (Mike Johnston) says: > I just put one of those sleek looking, floor standing hologen lamps in > my living room. Imagine my chagrin when after turning the lamp on I > tried to use my cordless phone and discovered a loud hum. > Incidentally, this hum varies with the brightness of the lamp. I.E the > lower I dim the lamp, the louder the hum in my phone. Help! What's a > guy to do? Is there any way I can shield my lamp from this or am I > just stuck? Sounds to me like poor power supply rejection in the base unit of the phone. Obvoiusly, the lamp has a dimmer in it, which would typically use some form of triac switching to achieve the dimming action. However, this results in rather sharp current rise times, which tend to get into everything else connected to the same supply. What is needed is some level of inductance in the supply to the lamp (it really should be built- in, if the manufacturer cared about the possibility of interference), but I can't quote any figures off the top of my head. A few tens of turns around a ferrite core should provide a signifcant improvement though. The other possibility is that the noise is being radiated RF-wise, but I'm assuming that the cordless phone is using FM, and that it has reasonable AM rejection, which should kill of dimmer noise. If this is the case, the solution is really the same - limit the rate of current rise in the lamp, using an inductor. I hope this helps. Mark