gst@gnosys.UUCP (Gary S. Trujillo) (02/05/89)
In article <432@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes: > In article <112@gnosys.UUCP> gst@gnosys.UUCP (Gary S. Trujillo) [me] writes: > >Maybe we could get Lenny, Gil, and John to design us an infrared interface > >for the keyboard... > > This is an interesting idea, but probably not all that practical... Hey, Gil - I meant that as a JOKE! :-) (Guess you missed the smiley, or thought it applied only to the part about the periscope. Oh well. Still, I appreciate the effort you put into giving the idea some thought. BTW, now that I have your attention, I would like to ask a serious question. I was talking with someone locally about the idea of an external hard disk, and mentioned the two independent projects currently underway. His remark was that one of the things he liked about the machine (being a ham radio operator) was how it was nice and self-contained, and very low on RF emissions. He says that once you start running external cables around that whole situation can change very drastically. Have you given any thought to that problem? Have you measured RF radiation, even by means of noting the effect of the external cable on nearby radio and television receivers? Same question to jbm. -- Gary S. Trujillo {linus,bbn,m2c}!spdcc!gnosys!gst Somerville, Massachusetts {icus,ima,stech,wjh12}!gnosys!gst
jbm@uncle.UUCP (John B. Milton) (02/06/89)
In article <116@gnosys.UUCP> gst@gnosys.UUCP (Gary S. Trujillo) writes: >In article <432@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes: >> In article <112@gnosys.UUCP> gst@gnosys.UUCP (Gary S. Trujillo) [me] writes: [keyboard joke] >BTW, now that I have your attention, I would like to ask a serious question. >I was talking with someone locally about the idea of an external hard disk, >and mentioned the two independent projects currently underway. His remark >was that one of the things he liked about the machine (being a ham radio >operator) was how it was nice and self-contained, and very low on RF emissions. >He says that once you start running external cables around that whole situation >can change very drastically. Have you given any thought to that problem? Have >you measured RF radiation, even by means of noting the effect of the external >cable on nearby radio and television receivers? Same question to jbm. Yes, I have. If you want to keep down EMI, you can (and this is my OFFICIAL position) buy shielded ribbon cable to run from my board to your external disk drive enclosure. As far as EMI from my board, I have not thought up anything for that. I suppose one could use some of that stick metal coated paper that they used around the bus board and in the monitor. Anyone know where I can get some of this? Would they also provide custome die cutting? John -- John Bly Milton IV, jbm@uncle.UUCP, n8emr!uncle!jbm@osu-cis.cis.ohio-state.edu (614) h:294-4823, w:764-2933; Got any good 74LS503 circuits?
gil@limbic.UUCP (Gil Kloepfer Jr.) (02/13/89)
In article <116@gnosys.UUCP> gst@gnosys.UUCP (Gary S. Trujillo) writes: >Hey, Gil - I meant that as a JOKE! :-) (Guess you missed the smiley, >or thought it applied only to the part about the periscope. Oh well. >Still, I appreciate the effort you put into giving the idea some thought. Guess so. It really WAS a neat idea though ;-) [RF and 2nd disk upgrades] >He says that once you start running external cables around that whole situation >can change very drastically. Have you given any thought to that problem? Have >you measured RF radiation, even by means of noting the effect of the external >cable on nearby radio and television receivers? Same question to jbm. >Gary S. Trujillo {linus,bbn,m2c}!spdcc!gnosys!gst >Somerville, Massachusetts {icus,ima,stech,wjh12}!gnosys!gst Ugh... I've already read John Milton's reply, and my position on it stands equally with his. In the hard disk upgrade instructions I'm distributing, I mention briefly the problems with RF interference. In that brief section, I discuss how BIG of a problem it is. I disagree with John on one point: I don't think shielding the cables will solve the problem completely, or even sufficiently. I've had a homemade expansion board INSIDE my machine for a while, buffering SOME address/data lines and sending them out through a ribbon cable wrapped in aluminum duct tape. The TV interference improvement was negligable. I think in order to keep the interference down completely, you will need to shield ALL parts of the upgrade, including the PC/perf-board. My guess is that the board would have to be put inside a shielded metal box. What further baffles me is that there are not constantly signals going to/from the hard disk. Why is there constant interference on a TV? I suspect that the cables are leaking other-than-disk signals outside the shielded cabinet. (see below) A "someone" who wishes to remain anonymous and who currently has the second hard disk upgrade in his 3B1 will get thrown out of the house by his family soon when they find that channels 2 (CBS) and 4 (NBC) on their portable TV don't come-in anymore because of a certain external hard disk. Sigh... ------- Gil Kloepfer, Jr. U-Net: {decuac,boulder,talcott,sbcs}!icus!limbic!gil ICUS Software Systems Voice: (516) 968-6860 [H] (516) 746-2350 x219 [W] P.O. Box 1 Internet: gil@icus.islp.ny.us Islip Terrace, NY 11752 "Life's a ... well, you know..."
jcm@mtunb.ATT.COM (was-John McMillan) (02/14/89)
In article <461@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes: >In article <116@gnosys.UUCP> gst@gnosys.UUCP (Gary S. Trujillo) writes: >... >>He says that once you start running external cables around that whole situation >>can change very drastically. Have you given any thought to that problem? Have >>you measured RF radiation, even by means of noting the effect of the external >>cable on nearby radio and television receivers? Same question to jbm. > >Ugh... I've already read John Milton's reply, and my position on it stands >equally with his. In the hard disk upgrade instructions I'm distributing, >I mention briefly the problems with RF interference. In that brief section, >I discuss how BIG of a problem it is. > >I disagree with John on one point: I don't think shielding the cables will >solve the problem completely, or even sufficiently. ... > What further baffles me is >that there are not constantly signals going to/from the hard disk. Why >is there constant interference on a TV? I suspect that the cables are >leaking other-than-disk signals outside the shielded cabinet. (see below) Wrapping them in duct tape? O brother! What is the attenuation of duct tape and how was it grounded? I'm sure EE's will respond to the issues here, so I'll skip on. RF isn't the source of all evils. In one case: Some years ago, and at a different company, an adjacent lab was troubled by mysterious crashes. ...Which stopped when they electrically isolated their equipment with line filters. A scope on the line showed they were pushing enough hi-frequency signal down the wire to be causing some sort of interference between machines. (This is what I was told, and accept.) In another case: Two years ago, a friend bought a maximally-cheap clone -- of Korean manufacture, if I recall -- from an odd little shop near his home in Maryland. He took the first unit back because it repeatedly died. The store, admirably, replaced the unit. Again, it frequently locked up: this time the store threw in an upgrade to a faster model -- for free! And it still belly'd up. I was visiting, and -- back at his friendly store -- convinced him to buy -- and Tom AIN'T easy to get in a BUYing mode -- one of those CRT-platforms that contains switched outlets and isolates each component on a spike-protected, noise-isolated circuit. (~$40?) Of course, at the same time the store also replaced the guts of the machine (what does their back-room look like with all these swapped parts?). Since then, the clone's been untroubled. - - - - Whew -- didn't anticipate the length of the above! Apologies. So: neither underestimate the effects of RF propagation from unshielded cables, nor depend on the INTERNAL isolation of your equipment -- in either direction! At home, use a spike-arrester with built-in noise filters to minimize line-carried interference. The TV interference on your neighbor's set may be RF, but on YOURS it may be house wiring. jc mcmillan -- att!mtunb!jcm -- speaking for himself only