A bit off topic, but likely interesting to time-nuts: In the early days of HDTV (late 80s - early 90s) we were at a European trade show and had to borrow, at the last minute, a large (~40") CRT-based HD monitor from a Dutch company that was also exhibiting there. We liked it so much that we purchased it for use at other trade shows. The very next show was in Sydney, Australia. The monitor would not converge and had funny rainbow patterns no matter how many times we degaussed it. Thinking it had been damaged in its half-way around the world shipment we called in the local representatives of the Dutch manufacturer and they were as stumped as we were. Finally, after they talked to engineers at the factory, the explanation was: "Of course, that is a Northern Hemisphere monitor; the earth's magnetic field is much different in the Southern Hemisphere. It can't work there.". After the show we shipped it back to our headquarters in California and, sure enough, the picture was perfect.
So, we had a HDTV monitor that doubled as a earth hemisphere detector, using magnetic flux differential. Needless to say, we only used it in northern hemisphere shows after that. Craig McCartney WA8DRZ -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Dave Baxter Sent: Thursday, April 15, 2010 1:03 AM To: time-nuts@febo.com Subject: [time-nuts] [OT] degausing The shaker system I used to know of, was used to test early mobile phone network test systems (with CRT monitors in) that were intended for "mobile" use, and no magnetic field leaked out of that one. It was the size of a small refuse bin, stood about 2' high, (3' dia) verticaly on the floor, bolted down to a huge block of concrete, and liquid cooled! The movement was only a couple of mm at most, but the force it could exert was silly. As for degausing things after the event... Hear at the salt mine, we have a HP 3GHz network analyzer with CRT display we used to cart arround the country when servicing RF power amps. One site, a MRI research facility, the "ambient" magnetic field is strong enough to screw the display off the screen if you are not careful how you position the analyzer. You can also feel your toolbox being pulled sideways when walking around the outside of the building. Never affected any credit cards though, even when I forgot I had one on it's own in a coat pocket! (The main Tech guy at that site could somehow screw an alloy plate into the field near the MRI scanner, let it go, and it'd sit there in mid air! If you tried to get it out, not knowing how, the harder you tried, the hotter it got. The Miensner effect I believe.) We often had to put the whole analyzer through a large home made delousing coil when back at the office to get the display straight again. OK, that was only a monochrome tube (green) but I personaly have also recovered normal shadow mask colour CRT's in TV's and monitors in the past, but it takes time patience, and a 9" coil that uses so much power it gets too hot to hold if you run it for more than 10 seconds! Remember too, to take the coil WELL away from the CRT before turning it off! I've also seen an old guy at a customers site in the past demag a small colour tube using a small strong permanent U shaped magnet on a stick, spun between his fingers while moving it arround the affected area. Absolute magic to watch him doing that. I guess he's long retired now, if not pushing daisies. Regards. Dave B. > ---------------Original Message-------------- > > Message: 6 > Date: Wed, 14 Apr 2010 12:12:46 -0400 > From: "Bob Camp" <li...@rtty.us> > Subject: Re: [time-nuts] time-nuts Digest, Vol 69, Issue 31 > To: "'Discussion of precise time and frequency measurement'" > <time-nuts@febo.com> > Message-ID: <4d4ef6b7d229491eab69ea5b551da...@vectron.com> > Content-Type: text/plain; charset="us-ascii" > > Hi > > I've found that in some cases you need to run multiple passes over > multiple days to degauss a badly mag'd monitor. I'm sure that at some > point they do indeed become "irreversible". So far I haven't found one > that a hula hoop sized coil won't eventually fix. > > Bob > > -----Original Message----- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Chuck Harris > Sent: Wednesday, April 14, 2010 8:15 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] time-nuts Digest, Vol 69, Issue 31 > > Dave Baxter wrote: > > > I think you'll find that any stray fields from industrial shaker > > systems, are often from the connecting leads, especialy if > not correctly > > positioned and layed out. The internal static and dynamic magnetic > > fields are "Very" well contained. > > Not necessarily. I did some shaker work at one company, and their > shaker magnetized the CRT's on any computer that was within several > feet of the shaker table. Sadly, the damage was irreparable. The > screens were left with permanent rainbow splotches here and there even > after running a degaussing coil over the entire monitor. > > -Chuck Harris > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > > > ------------------------------ > > Message: 7 > Date: Wed, 14 Apr 2010 12:33:17 -0400 > From: Chuck Harris <cfhar...@erols.com> > Subject: Re: [time-nuts] time-nuts Digest, Vol 69, Issue 31 > To: Discussion of precise time and frequency measurement > <time-nuts@febo.com> > Message-ID: <4bc5ee4d.1030...@erols.com> > Content-Type: text/plain; charset=UTF-8; format=flowed > > Bob Camp wrote: > > Hi > > > > I've found that in some cases you need to run multiple > passes over multiple > > days to degauss a badly mag'd monitor. I'm sure that at > some point they do > > indeed become "irreversible". So far I haven't found one > that a hula hoop > > sized coil won't eventually fix. > > > > Bob > Sadly, I have. I used a large degaussing coil that could be passed > over the entire monitor, a smaller bulk tape demagnetizer, and the > internal degaussing coil. I could never get rid of the rainbow fringe > around the outside of the CRT. > > -Chuck > > > > ------------------------------ > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > End of time-nuts Digest, Vol 69, Issue 34 > ***************************************** > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
