0003829147@mcimail.com (Sander J. Rabinowitz) (08/25/90)
In reference to a TELECOM issue of 24 August 1990, Tom Neff <tneff@ bfmny0.bfm.com> wrote the following: "I turned on the shortwave receiver in my apartment this morning and was flipping past the 5-6 MHz neighborhood when I distinctly a voice coming from the speaker. It was my friend in the other room! I couldn't believe it. . . ". . .So I started unplugging things. Speakers... no. Radios... no. The phone itself... no. The answering machine... YES! . . ." The message went on to ask whether other Panasonic answering machines broadcast on radio frequencies. Tom Neff's machine was a Panasonic KX-T1470. I own a Panasonic KT-T1450 which I had purchased only 48 hours ago on sale at a local KMart, as well as a Sony ICF2010 shortwave receiver, and I wanted to see if I could recreate the above events. As it turned out, when the answering machine was idle but turned on, it did send out signals on 5,655 kHz. I then hooked up my tape recorder to the radio, and deliberately started speaking within various distances from the answering machine. When I played the tape back, I did recognize my voice, but it sounded so muffled as to make the signal useless for intrusion purposes. Two other things I noticed with my model: 1) The signal cuts off when the tape players are activated. In other words, it appears that telephone messages do not get sent over the air. 2) The apparent strength of the answering machine signal seemed to depend on whether or not the short wave receiver was plugged into an A.C. wall socket. When it was plugged in, I could pick up the signal as described above, but when the radio ran off of batteries, the receiver had to be practically next to the answering machine for the signal to be received. My tentative findings, then: Yes, the answering machine may be broadcasting, but a) the audio distortion is horrible, and b) the signal may not travel far beyond the confines of your living room. * * * Sander J. Rabinowitz 0003829147@mcimail.com * * *
petrilli@walt.cc.utexas.edu (Chris Petrilli) (08/27/90)
In article <11340@accuvax.nwu.edu> 0003829147@mcimail.com (Sander J. Rabinowitz) writes: >In reference to a TELECOM issue of 24 August 1990, Tom Neff <tneff@ >bfmny0.bfm.com> wrote the following: >"I turned on the shortwave receiver in my apartment this morning and >was flipping past the 5-6 MHz neighborhood when I distinctly a voice >coming from the speaker. It was my friend in the other room! I >couldn't believe it. . . > [. . .] When I played the tape back, I did >recognize my voice, but it sounded so muffled as to make the signal >useless for intrusion purposes. [... he continues by noting that when plugged into the AC wall socket, he is able to receive a much stronger signal than when running off batteries...] Being someone interested in radio propagation, and working with alot of radio equipment, it would appear to me that electrical circuits in both the answering machine, and your Sony radio are not too well isolated from AC noise. Apparantly, the Panasonic machine is modulating the AC carrier in some way, and your radio is picking that up ... this means that it would most likely be just as strong at your neighbors house (as long as you are on the same power transformer). I could be wrong, but this would be the most likely cause of something like this happening ... you might try isolating the Panasonic from the wall with some sort of line filter (I like the DEC VAX filters myself, but...) that goes through an isolation transformer ... if it still appears, I'm wrong. + Chris Petrilli "Opinons represented here | University of Texas at Austin do not necessarily | INTERNET: petrilli@ccwf.cc.utexas.edu represent those of a sane | SNAILMAIL: 429 Brady Lane, Austin, Texas, 78746 person. Take them as + PHONE: +1 512 327 0986 simply that."