(Semi-OT) Looking @ getting LCD/LED monitor 4 PC, need advice re: RFI

[pianoplayer88key]

Hi all...

I'm looking at possibly getting an LCD / LED computer display maybe in the next few months. (I'm currently sharing my computer with my mom, and she's wanting to get her own soon. She'll be keeping the display as it's hers anyway.)
I'll probably ask in more detail (advice on specific specs, like contrast ratio, brightness, etc) on a more computer-oriented site, but basically I'm probably looking at something between 20 and 24 inches, 1920x1080 minimum resolution, decent for gaming, watching movies, etc, preferably under $200, or not much over.

A main reason I'm asking about it on here is related to RFI on broadcast bands. The CRT we're currently using puts out some nasty RFI on several frequencies, and raises the noise floor throughout the AM band. At its current setting, for example, a local station on 600 kHz (5 kW at 8 miles, fair to good ground conductivity per M3, something like 40 to 70 mV/m per v-soft zip signal) is nearly inaudible with my portable radio sitting on the keyboard tray or on my lap. (Changing the resolution or refresh rate changes the frequencies that have extra-strong RFI.)

What do I need to look for in an LCD monitor to help eliminate the RFI while it's operating? I would like to be able to set my battery-operated AM radio (Tecsun PL-606 or Sony SRF-59 being the most likely ones at this time) on the desk, keyboard tray, wherever, without the display degrading reception of weak (for example 25 to 100 µV/m) signals. (Setting the radio on the computer tower also degrades reception, but not nearly to the levels or at the distances that the current CRT does.) If I could actually DX (e.g. have near-armchair level on a mid power level (5 kW), middle-of-band (1100 kHz) signal over average (8 mS/m) ground from 200-300 miles away, using the radio's built-in ferrite loopstick (not taking into account blocking/desense/splatter caused by nearby locals)) while my radio is actually TOUCHING the operating display, that'd be nice, but if not, what's the next best I could hope for?

I may mail-order a display, but I do plan to go to a few local stores and look at them in person before I decide which one to buy. Should I take an AM radio in there, even though reception (especially in a building like Fry's) will be virtually nil as my local Fry's doesn't have a 50kW with its very efficient (at least 511.77 mV/m @ 1 km for 1 kW applied power - figures pulled from KSTP data) stick rising up from inside the store, and check for RFI on the displays? (Assuming that I'm unable to receive any locals, maybe I should take a 2nd radio whose local oscillator I could tune for?)

TY & 73

 

[kenglish]

I had a discussion with the guy who is in charge of RFI Protection for the big Radio Telescopes, a while back. One of his colleagues has been doing some work on this. Basically, you need to completely rebuild the monitor ;D .

Seriously, though, your first thought should be to find one that runs on an external power supply. The internal switch-mode supply makes tons of RFI. With an external one, you can shield and filter it, or (better yet) use a linear power supply.

Next, get rid of any inputs and cables that are not necessary. Then, filter the ones that remain..probably need some torroids that are designed for the MW band. He even removes the driver chips from the unused inputs and outputs, but that's a bit drastic for most of us.

Which leads to the next thing......He actually shields the entire monitor guts (all but the screen) with copper sheeting. That's going way beyond most people's means, but you might want to add some screening over the rear of the plastic case, or use some sort of RFI-proof Shielding Spray (like paint, but conductive) in the inside of the case. There is also some conductive, see-thru cloth available, if you wanted to add that over the screen...in an extreme case.

Using some ferrites on the keyboard and mouse cables can also help with computer RFI. Be sure to use the formulations that are specific to Medium-wave and HF frequencies, though. The Radio Shack ones may not help below 25 MHz, if they are like most (I haven't tested them all yet).

Always try to power the computer and the radio on separate circuits. An external antenna is best....one of those loop antennas will allow you to null-out much of the noise, though. MFJ makes a nice power filter/four-port receptacle for Hams and SWLs, too.

 

[pianoplayer88key]

I had a discussion with the guy who is in charge of RFI Protection for the big Radio Telescopes, a while back. One of his colleagues has been doing some work on this. Basically, you need to completely rebuild the monitor ;D .

... which would probably cost more than I'm hoping to pay for the monitor itself! (I'm hoping to keep it under $200-250 or so.)

Seriously, though, your first thought should be to find one that runs on an external power supply. The internal switch-mode supply makes tons of RFI. With an external one, you can shield and filter it, or (better yet) use a linear power supply.

So if it doesn't have a wall wart (or in-line transformer package) it uses an internal supply? (I also assume I should avoid one that's powered through the computer, right?)

Next, get rid of any inputs and cables that are not necessary. Then, filter the ones that remain..probably need some torroids that are designed for the MW band. He even removes the driver chips from the unused inputs and outputs, but that's a bit drastic for most of us.

At this point I'm not totally sure what inputs I'll need. I believe my current one uses the old analog VGA standard. My current computer doesn't have a DVI out, but it does have HDMI - maybe that might work for the display? (I don't expect to be opening the guts of this display to remove driver chips, at least not until after the warranty expires, if ever.)

Which leads to the next thing......He actually shields the entire monitor guts (all but the screen) with copper sheeting. That's going way beyond most people's means, but you might want to add some screening over the rear of the plastic case, or use some sort of RFI-proof Shielding Spray (like paint, but conductive) in the inside of the case. There is also some conductive, see-thru cloth available, if you wanted to add that over the screen...in an extreme case.

Yeah that copper might be a lot of $$$! (Replacing the bass strings in a piano costs the technician a few hundred bucks or so JUST for the parts, or just ONE string is like $20 to $30 or so.) I wonder if that RFI-proof spray might work, though. Hopefully I won't need to add the cloth over the screen, as I would like to keep accurate color reproduction, good ability to see details in shadows AND highlights, etc.

Using some ferrites on the keyboard and mouse cables can also help with computer RFI. Be sure to use the formulations that are specific to Medium-wave and HF frequencies, though. The Radio Shack ones may not help below 25 MHz, if they are like most (I haven't tested them all yet).

I've heard of ferrite chokes, but don't know much about them yet. You think that would help curb RFI to a nearby battery-operated radio?

Always try to power the computer and the radio on separate circuits. An external antenna is best....one of those loop antennas will allow you to null-out much of the noise, though. MFJ makes a nice power filter/four-port receptacle for Hams and SWLs, too.

Yes, the computer and radio are on separate circuits, if that's what you call it. The radio is powered by the 110V AC power, and the radios are powered by NiMH Sanyo Eneloop 1.2V AA batteries. As for using an external antenna, that would be impractical, as I do move around quite a bit, including fairly frequently bicycling a few miles from home. (BTW putting the radio right up against the current CRT's screen results in some signals that on the PL-606 indicate higher signal strengths than my local 50kW sticks 7 and 9 miles away... but then I don't normally try to listen to stations when the radio is THAT close. )
So what about that MFJ filter ... what would be some advantages?

 

[spunker88]

HDMI is DVI plus digital audio, the audio pins are not used on DVI. So you can get a HDMI to DVI conversion cable pretty easily since its a simple conversion done inside the cable. VGA can always be used but the low quality cables included with the monitor usually have poor shielding and thin wire gauge which can lead to a washed out picture since VGA is analog. DVI/HDMI is digital, so just like DTV its 100% picture or nothing.

I know LCD displays use a CCFL which is a small fluorescent type bulb for the backlight. I imagine this uses some sort of ballast to start the bulb just like regular fluorescent lighting does. This could be a potential source of interference. On a LED display, leds are used to backlight. The LEDs themselves shouldn't give off much noise but the transformer used to make DC power for them would. I have seen LED monitors with external power bricks. LED monitors are so thin that there really isn't room to house the transformer on the back, so instead it is included in line on the wire. This is nice because it allows you to get the power brick away from your radio. LCD monitors usually have room to house the transformer inside the monitor since they are slightly bulkier due to the CCFL backlight.

I'd say its worth it to find a LED monitor with an external power supply. The power brick could be shielded and kept as far away as possible. You are still going to have interference fed back into the AC line from the transformer, but I imagine your radio isn't on the same circuit as the computer stuff anyways.

 

[pianoplayer88key]

Ah ok. Looks like I'll be looking at getting an LED-backlit display then. One requirement is it be at least as "quiet" as my 4 AA powered white LED bicycle light which I also am using as a flashlight. (I can put it right up against the AM radio tuned to a blank channel and not notice any interference, except maybe a brief click when I switch the light on, dim & off.)
So far I've posted requesting advice on 3 different forums (they're independent sites, so I hope that's not considered "cross-posting" ), and may also ask in an IRC chat room as well. One reply already mentioned the possibility that my current video card (ATI X1250 integrated into the Gigabyte GA-MA69G-S3H motherboard) may not support the 1920x1080 resolution. If I have to get a new card, that would be included in the budget, but my post on here is mostly for the purpose of preventing RFI before it happens, preferably.

 

[spunker88]

If it has HDMI then it must be a fairly modern card and should support 1920x1080. It probably won't allow gaming or anything graphically intense at that resolution, but web browsing, etc should work fine. But it is an integrated card and they are usually lower end than dedicated cards. If you want to spend another $20-$30 pick up a PCI Express dedicated graphics card from Newegg, they usually have good prices on this stuff. But you shouldn't need to unless you plan on doing something graphically intense at a high resolution. You can always lower the resolution, but LCD/LED monitors look best at their native (highest) resolution, unlike CRTs which look the same at all supported resolutions.

 

[pianoplayer88key]

I'm running the few games I play in a window at 640x480, sometimes I'll step it up to like 960x600 or 1024x768 or something like that. Also I currently rarely watch videos over 1280x720, and most are lower than that. I do like plenty of working area for my desktop, and maybe in the future when I have a better video card, faster CPU, hard disk, etc, I would be watching some 1080p video.
And yeah, I know that about LCDs really only looking good at their native resolution. I wish I could get something as thin as an LCD that's as scaleable as a CRT, but I don't know of anything.

 

[Darth_vader]

Plasma screens?

I had a friend who used a Samsung plasma screen which handled lower resolutions at least as well as my Viewsonic G90FB. These are probably just as noisy as a CRT, tho.

 

[kenglish]

Plasma TVs are regarded as the "Kiss of Death" by Hams. Very noisy.

 

[spunker88]

Plasma is a definite no. You could always go with a lower resolution monitor if you don't think you'd have a use for 1920x1080. But this resolution will probably become the standard for computers since its also what 1080p television uses.

 

[pianoplayer88key]

Yeah plasma is definitely not under consideration because of the noise! I'm seriously looking at LED - hopefully it's at least as quiet as my 4-AA-powered LED bicycle headlight. (I can put it right up to my Tecsun PL-606 or Sony SRF-59 tuned to an unused channel and not hear any noise from the light, except maybe a click when I switch it on and off (but I need to check/verify that.))
I remember seeing a post where someone said a neighbor's plasma was stronger than some TIS stations! Considering that I have one 15 miles away that with a good antenna is nearly full-quieting, and I may often have my radio within a few millimeters of the display (using only the radio's built-in ferrite), it looks like plasma is O-U-T: OUT! For curiosity I did look on newegg at plasma TVs, and the smallest I saw was around 42 inches or so. I was just in Fry's a little while ago looking at their displays, and concluded that 27 inches is a bit bigger than I need. (I'm mostly looking at 20 to 24 inches.)

As for resolution, while I'd like to be able to occasionally run lower resolution, most of the time I expect to be using 1920x1080. I'd love to get one capable of 2560x1600, but I'd have to increase my budget by a factor of 6 or more.

P.S. I'm wondering why I've gotten better / more replies on here than on all 3 of the more tech/computer-oriented sites combined I've posted asking for display recommendations? (I did post a bit different there - didn't emphasize RFI as much, asked more about specs like brightness, contrast ratio, response time, etc.)

 

[carmen]

im using some ultracheap ACER about 3 feet from my antenna ( 2 turns of copper pipe, with an additional 2 turns of wire clippable in for 160/MW) and it's fine. key is ground the crap out of everything. get some clip leads, use USB shield or VGA lug grounds on laptops/PCs, ground to house ground, yadda

also run like 10 feet of coax to your antenna and coil it around some 6 inch plastic container around 5 times to choke off RFI getting to the antenna

 

[carmen]

r

Which leads to the next thing......He actually shields the entire monitor guts (all but the screen) with copper sheeting

high end monitors, eg EIZO probably still do this. i used an NEC picked up at an ENRON asset auction, made in japan and completely encased in a faraday shield with small vent holes punched into it. yes it was quiet, even without a proper common-mode rejecting magloop / 1:1 choke balun

 

[boiseengineer]

Slightly off topic. FCC visited a poor family in Oregon when their brand new plasma TV was transmitting on one of the ELT (Emergency Locator Transmitter) frequencies. Gave them a NOV on the spot & made them turn it off.

I have very little problems with Acer or Dell monitors. Even the two LCD HD TV's are clean.

Its the UPS's and CableOne's digital leakage that cause a lot of havoc from DC to 200+ MHz.

 

[pianoplayer88key]

Carmen, that sounds good, except I don't think that would work very well in my situation. this photo and this one should give you some ideas as to how large my antennas are and where they typically are in relation to the radios I'm primarily using. Therefore I'm hoping to eliminate the RFI at the source, and still be able to use said device. (I'd rather get one that's designed properly to not radiate much if any RFI, rather than get something noisy and have to deal with it later.)

Would it be too unreasonable to expect a LED-backlit LCD display to be at least as quiet as my LED bicycle headlight / flashlight, or quieter? (The light is powered by 4 AA batteries.) I just tested it inside my brother's pickup truck (to reduce the desense caused by strong local MW stations) versus my Tecsun PL-606. With the light on at full power, there is no detectable interference throughout most of the AM band. Set to dim, there's a little buzz audible from the upper reaches of LW (just below the MW band) up to somewhere around the 1500s or so, which goes away when the light is an inch and a half away or so from the radio. (At full brightness there is a little bit of desensing (but not enough to register on the dBu display) at the upper end (I tested on 1680 kHz), which goes away with a 1 to 1.5 inch separation. There was no detectable interference at 2300 kHz, the lowest the PL-606 will tune in SW, nor was there anything noticeable at 279 kHz, the highest official LW broadcast frequency overseas (or anywhere below, including 153 kHz). There was a slight buzz noticeable around 400 kHz or so.

Also I've heard good things about Samsung and LG displays, and have in the past had good experience (generally - there was an exception but I forget the circumstances now) with ViewSonic CRTs. (I'm not talking about RFI here though.) Does anyone know about the current quality of their LCD panels?

Also shouldn't that plasma TV's erroneous radiation be the responsibility of the manufacturer, not the end user?

 

[carmen]

probably a 1AA flashlight? noisy DC-DC converter wipes out LW within a few feet of a coil here. switch to a 123A style flashlight and it will get 4V straight from batt and not need the RFI-inducing inverter.

theres a whole plethora of literature out there on differential-mode antennas and RF chokes. if you really want to explore, you'd proably do well to upgrade to a Tecsun PL660 or similar with an ANT input. the abiility to get the antenna even 5 or 10 feet awwy from a PC / screen is priceless

 

[carmen]

or perhaps modify the 606 for an external ANT connector. notice Hams with a pair of 23" displays and a PC sitting right next to their radio? a decently engineered antenna a decent distance from a (shielded) reciever in a properly grounded shack, and it doesnt really mtater how noisy the monitor is. you will be hard-pressed to find one that didnt skimp on shielding, filters/chokes in the power-supply, at consumer price level. the SAMSUNG 18" which was making tons of noise, i opened up (made in Mexico!) and shook my head in disbelief.

i'd seriously just look for a NEC 1850X on ebay. probbaly cheap by now

 

[pianoplayer88key]

I can understand a desire to get the antenna away from the noise source, but then it wouldn't be portable operation any longer. I usually take the radio with me when I leave the computer, or bring it with me when I come to the computer. Having it hooked up to an external antenna would make that impossible (especially considering I usually take it on my bicycle on errands around town). (I'm not aware of any type of antenna lead-in that will allow me to ride several miles around town (or take a bus several dozen miles across the county) with my radio connected to a fixed-location antenna, but I'm open to correction.)
I would prefer to tame the noise at the source, rather than get the antenna away from the noise.

Also I'm looking at current displays, not older ones. (If there's one that's quiet that I should consider, though, and otherwise meets my specs, maybe I'll take a look.) That NEC is only 18" (I'm looking at 21-24"), 1280x1024 not widescreen (I'm looking for 1920x1080 widescreen), and was probably made before anyone would have dreamed LED backlights would be mainstream and relatively cheap. (Aren't LED backlights quieter than CCFL?)