++++++++++++++++++ See also TVI ++++++++++++++++++ Date: Fri, 14 Jun 2002 01:34:53 +0100 From: pjhend at ameritech.net To: Elecraft at mailman.qth.net Subject: [Elecraft] Monitor noise I'm nearing the end of my rope....... I've been trying to "noodle through" the problem of horrible noise to my K2(and other HF rigs) from my Compaq Presario MV500 computer monitor. I picked up a boatload of snap-on and varried ferrite beads of all shapes and sizes and installed them on every cable coming in and out of the computer and monitor and power cables to the radio and computer. There was no change in the noise which is 7khz wide and appears every 50khz or so on almost every band. (Also, my radio and computer equipment is grounded to a ground strap connected to a cold water pipe 4' from my operating desk. ) It seems that the problem might lie in the design of the monitor, but I'm trying to avoid buying another one. Has anyone had any success solving this problem? Or, can anyone recommend a different compatible monitor that solved their problems? Any thoughts on the flat-screen monitors? I'm quite sure that I'm missing oodles of DX hidden behind these various "walls of noise" :-) Thanks! Paul kb9yvp ++++++++++++++++++ From: "Mike McCoy" To: , Subject: Re: [Elecraft] Monitor noise Date: Fri, 14 Jun 2002 08:00:59 -0500 Have you also tried changing the Horiz and/or Vert refresh rate of the monitor? Have you tried putting some distance between the monitor and your rig? In any case I suspect short of buying a Tempest certified system (e.g. totally shielded) pretty much all consumer level monitors (and PC's) are going to generate RFI... and certainly some worse than others. There are, after all oodles of 'oscillators' in those things. Also good, quality full metal case for the PC is a must (and plug up those open slot covers!) Back in the mid/late 80's Compaq USED to design/manufacture really top quality 'mil spec' stuff. No more tho, not in this day of the Dell/Gateway/etc. cutthroat consumer market. Besides for those 'everything for $900' deals I'd bet the Dells/Gateways/Compaq's OEM their montors anyway, probably paying no more than $50 a pop from some offshore company. Best to stick to manufacturers whos ONLY business is quality monitors, e.g. iiyama, EIZO-Nanao. Or otherwise a large manufacturer that at least has a division dedicated exclusively to monitors (Panasonic/Viewsonic, IBM, NEC, etc.). Besides, long term you are not doing your eyes a favor by having a cheap monitor. Trust me on this one, after staring at monitors for over 25 years, my eyes can no longer focus on anything under 3 ft away (I now have a pair of special prescription glasses exclusively for computer work). Same thing with keyboards (carpel tunnel anyone?). To avoid any future health related problems there are three 'human/computer interface' things you should never compromise on: the monitor, keyboard & chair. I have both an NEC and a Panasonic. Both exhibit some RFI but nothing really significant. However, it IS there though so I will shut them down if I'm doing any weak SWL or wanting to really dig down deep for DX. I also have my shack layout such that my PC/Monitor is on the opposite side from my rigs in my 10X12 'shack' room (maybe 8-10 ft away). I use double shielded 'coax' (98% braid + foil) for audio links to/from the soundcard. Hope that helped. 73, Mike - AD5IU +++++++++++++++++ Date: Fri, 14 Jun 2002 09:14:27 -0400 From: Margaret Leber To: Elecraft at mailman.qth.net Subject: Re: [Elecraft] Monitor noise Mike McCoy wrote: > In any case I suspect short of buying a Tempest certified system (e.g. > totally shielded) pretty much all consumer level monitors (and PC's) are > going to generate RFI... and certainly some worse than others. Rather than kill yourself trying to quiet an inherently RF-intensive technology, check out some LCD displays, too. While you won't find them for free out at the curb on trash day, and they're not *totally* free of RF emissions, they tend to be a *whole* lot quieter than CRT-based displays. 73 de Maggie K3XS -- -----/___. _) Margaret Stephanie Leber / "The art of progress / ----/(, /| /| http://voicenet.com/~maggie / consists of preserving/ ---/ / | / | _ _ _ ` _AOPA 925383/ order amid change and / --/ ) / |/ |_(_(_(_/_(_/__(__(/_ FN20hd / change amid order." / -/ (_/ ' K3XS .-/ .-/ ARRL 39280 /___ --A.N.Whitehead ___/ /____ICQ 7161096_(_/_(_/__AMSAT 32844____/ ++++++++++++++++ Date: Fri, 14 Jun 2002 07:53:55 -0700 From: Vic Rosenthal Organization: Transparent Software To: pjhend at ameritech.net, Elecraft Subject: Re: [Elecraft] Monitor noise -- snip -- Instead of worrying about the generation and radiation of RF by the monitor, let's look at how it's getting into your receivers. What kind of antennas do you have? An end-fed wire coming into your shack will always be prone to pick up RFI. The most RFI-resistant antennas are: 1) A balanced antenna fed with balanced line and tuned with a true balanced tuner. 2) A balanced antenna fed with coax with a balun at the feedpoint (the balun stops RFI flowing on the feedline from getting into the antenna itself). 3) An unbalanced antenna such as a vertical fed with adequate decoupling at the feedpoint. The idea is to get the antenna away from the shack, and -- once the antenna itself will not pick up the RFI -- prevent RFI that is picked up in common mode on the feedline (which of course has to be near the interference source) from getting back into the antenna. It's a myth that coax is more immune to RFI than balanced line. Both will work fine if used properly, and both will pick up RFI if not. In either case, the trick is to prevent common-mode currents from flowing up to the antenna and thence down to your rig. Vic K2VCO Fresno CA ++++++++++++++++ Date: Fri, 14 Jun 2002 10:25:38 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: pjhend at ameritech.net Cc: Elecraft at mailman.qth.net Subject: Re: [Elecraft] Monitor noise Paul, first thing I would do is to remove that common "ground" connection between the computer and the rest of the station equipment. In fact, if you can, plug the computer into a different branch circuit from that used for the radios. I separate my radio and computer and audio equipment this way and then use isolation transformers in the soundcard audio lines in and out. Have you tried other computers/monitors? Is the problem unique to either of yours? Lots of angles here, but that common "ground" (which is just a connection - not a "ground" at all) strikes me as not only unnecessary but probably a major cause of the problems. 73/72/oo, George W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 56th year and it just keeps getting better! QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735 Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437 +++++++++++++++ From: "ZOOM" To: , Subject: Re: [Elecraft] Monitor noise Date: Fri, 14 Jun 2002 12:18:36 -0400 Hi Paul; Have you considered it may not be your monitor making all the noise! The power supply can also be a big source of noise. I was getting S9 of noise in my shack. I too thought the monitor was the culprit but discovered it was not the monitor but the power supply in my computer. I bought a better quality power supply and the noise is gone. Yes monitors can be a source of noise but also check the power supply in your computer. A cheaply made supply will generate allot of noise even though it's in the case. Regards, Robert VE3RPF ++++++++++++++++ From: "Pat J. Whelton" To: , Subject: Re: [Elecraft] Monitor noise Date: Fri, 14 Jun 2002 14:32:36 -0500 Hi Paul. I have the same problem with a Compaq Presairo 5170 and MV700 monitor. My problem is severe in my K1 on the FISTS calling frequency 14.058 and also on 14.005. I have to power off the monitor if I want to work those frequencies. Here's another trick someone showed me on QRP-L that might help you. Go into the Windows control panel, display, settings tab and change the monitor resolution from 800X600 pixels to 1024X768 pixels. This will not get rid of the crap but it will move it up frequency and away from the frequency you want to work. It will also allow you to use your monitor and your logging software. Good luck. Pat - KZ5J http://u1.netgate.net/~kirby34/rsg/wheltonp.htm ++++++++++++++++++ Date: Fri, 14 Jun 2002 23:56:30 -0700 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Monitor noise To: Elecraft Mailing List Paul; Any CRT display generates strong magnetic fields at the harmonics of the vertical and horizontal sweep rates. These fields are used to sweep the electron beam across the CRT. On standard US television, these occur at 60 Hz and 15.75 kHz. On a computer monitor, the vertical rate is usually 75 or 85 Hertz and the horizontal frequency is dependent on the vertical sweep rate and the horizontal display resolution. For instance, a 1024 by 768 pixel display with an 85 Hertz refresh rate will have a horizontal sweep frequency of 68 kHz. These magnetic fields are extremely difficult to shield. Most TV's and monitors these days have some magnetic shielding, but much of the energy still leaks out. In the early days of TV, there was no magnetic shielding and most TV's would generate significant harmonics in the lower frequency ham bands every 15.75 kHz. There is much less of a problem these days because there is now some magnetic shielding even though its primary purpose is to keep magnetic fields from distorting the colors you see on the TV. Computer monitors are a worse problem because the higher frequency of the horizontal sweep can generate significantly higher HF energy. The FCC rules regarding computer radiated emissions don't start until 30 MHz, so by law there is no requirement to limit the radiated emissions in the HF bands. As with TV's, the magnetic shielding that is used is designed to prevent color contamination in the display, not to limit HF radiated emissions. Improved grounding or removing grounding of the computer and monitor shouldn't have much effect on the magnetic field emission. I doubt whether any conventional shielding would remove the problem; you have to use a ferro-magnetic type of material to reduce these types of fields and it would have to completely surround the monitor. Changing the vertical refresh rate or the display size could move the problem to a different frequency. The one other method of attacking the problem is to determine if it is coupling in at the antenna or the transmission line. If you disconnect the transmission line at the antenna end, does the level decrease or stay the same. If it decreases, the energy is coming in via the antenna and the only way to reduce it is to locate the antenna further away. If it stays the same, disconnect the coax from the receiver. If it decreases, the noise is entering by the coax. This can sometimes be reduced by putting a common mode choke on the coax. If it stays the same, it is coupling directly into the receiver either via the power connection or directly through the receiver case. A power connection problem can usually be helped with a common mode choke on the power feed. If it is directly entering the receiver, moving the receiver away from the monitor will reduce the noise level. Hope this provides some ideas on how to attack this type of problem. -John KI6WX ++++++++++++++++ To: KI6WX at pacbell.net Cc: elecraft at mailman.qth.net Date: Sat, 15 Jun 2002 08:28:12 -0700 Subject: Re: [Elecraft] Monitor noise From: k6se at juno.com John, KI6WX wrote: "The one other method of attacking the problem is to determine if it is coupling in at the antenna or the transmission line. If you disconnect the transmission line at the antenna end, does the level decrease or stay the same. If it decreases, the energy is coming in via the antenna and the only way to reduce it is to locate the antenna further away. If it stays the same, disconnect the coax from the receiver. If it decreases, the noise is entering by the coax. This can sometimes be reduced by putting a common mode choke on the coax." ========== John is absolutely right. Magnetic fields do not radiate very far, so virtually all birdies that you hear that are generated by the computer monitor are picked up either by the receiving antenna if it is closeby or by the feedline if it is poorly matched and has common mode currents on it. There's not too much more that you can do than what he suggests. 73, de Earl, K6SE 74 countries with K2 #2622 and counting..... ++++++++++++++++++ From: "Ken Lotts" To: "Helmut Usbeck" , "Bob - AG5Q" Cc: Subject: RE: [Elecraft] TV interference Date: Fri, 24 Jan 2003 05:28:46 -0700 I solved my (very serious) Computer monitor TVI situation by just experimenting with different "refresh" frequencies inside the properties of my video adapter. It works! (Currently my best results are at 85 Hertz). Ken aa7jc -----Original Message----- From: elecraft-admin at mailman.qth.net [mailto:elecraft-admin at mailman.qth.net]On Behalf Of Helmut Usbeck Sent: Thursday, January 23, 2003 3:49 PM To: Bob - AG5Q Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] TV interference One reason I use a laptop in the shack is lower, or in my case no hash or trash from the monitor. My other machine using a CRT made most of my receivers useless on many bands. Alot of TV's, VCR's and appliances cause reverse "TVI". Actually it's all a consiracy against me, because I used to cause such TVI years ago with my homebrew six meter rig. Regards, Helm. WB2ADT [2698] On Thu, 23 Jan 2003, Bob - AG5Q wrote: > A few weeks ago someone warned about serious TVI from plasma TVs (that is, > interference TO the ham rig, not from the ham rig). > > Can anyone compare the potential for interference from ordinary computer > crt monitors to that from LCD monitors? I've noticed some birdies from the > crt monitor when my K2 is only a couple of feet from it but they're spaced > about 70KHz apart and it's (almost) livable. I'm wondering if an LCD > monitor would be better or worse? > > If anyone has a suggestion for reducing this kind of problem, I'm all ears. > > 73/ Bob - AG5Q +++++++++++++++++ Date: Fri, 24 Jan 2003 10:46:20 -0700 From: "Mike Lewis" To: AG5Q at attbi.com, elecraft at mailman.qth.net Subject: [Elecraft] RE:TV interference Hi, Our little group of hams has done a few of comparisons on this. As it turns out, it is not a simple answer. All my TVs are currently CRT based, non-HDTV types, so I cannot speak directly to issues with TVs per se, but possibly some part of this set of experinces, hearsay, and propaganda might be useful to you. Plasma displays are NOT the same technology as your typical LCD display which are either passive, or nowdays TFT active technology). I have also heard that plasma displays can cause significant interference to HF receivers, although I personally do not have any experience with this. As for LCD computer monitors, they are better than their CRT counterparts for interference, in general. I have used an older laptop for my shack for quite a while for this very reason. The stand alone LCD monitors are good too - as long as the power supply used to run them is not a culprit. A friend of mine has bought 3 LCD monitors for his shack. All 3 had noisy power supplies. The first two were actually powered by a 12v external switching brick (like used with many laptops), he simply canned those and powers them with his Astron station supply. Quiet as a mouse. The third one was powered internally, and would have needed siginificant surgery to be modified for external power. He ended up giving that one to his wife, whose system is at least in another part of the house. I try not to use CRTs in my shack. I will most likely eventually upgrade my shack PC to either a better laptop, or an LCD based desktop (after paying attention to the power supply issue). Unfortunately, many LCD monitors now have the power supplies built in. This does not necessaily mean they would be problematic, but I would make sure the return policy is to your liking first... 73 de KE0MF/Mike +++++++++++++++ From: "Bob - AG5Q" To: Date: Sat, 25 Jan 2003 09:58:04 -0600 Subject: [Elecraft] TV interference Thanks to everyone who replied to my question about noise from LCD monitors vs. CRT monitors. Feedback from users indicate the LCD monitor is generally quieter, sometimes a lot quieter. There may be an occasional exception, perhaps because of the power supply. Next time I get a new computer, I'll try the LCD monitor :) 73/ Bob - AG5Q +++++++++++++++