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eHam Forums => RFI / EMI => Topic started by: AA9G on March 06, 2014, 10:19:16 PM



Title: Computer monitor RFI
Post by: AA9G on March 06, 2014, 10:19:16 PM
Just wondering if monitors are a major source? In comparing LCD vs LED is one better? I am setting up a station that may end up with 4 monitors.
If it matters I will be running a K3.


Title: RE: Computer monitor RFI
Post by: K5LXP on March 07, 2014, 06:03:20 AM
LED monitors are LCD.  Just a different backlight, formerly cold cathode tube.

In my experience most monitors radiate some level of grunge.  However, it would take a pretty strong source of interference to radiate very far.  So the upshot of that is if you have sufficient antenna isolation it usually isn't a problem.

If your chassis grounds are part of your antenna system via common mode, it wouldn't take much of an interference source to cause a problem because your monitors are effectively just feet from your antenna.  So it has less to do with what rig you're running and more to do with your antenna.  It works both ways too.  With poor isolation you can cause computer problems when you transmit.  People go through all sorts of remedies like ferrites, different keyboards, mice, monitors etc to resolve what is likely local incident overload.


Mark K5LXP
Albuquerque, NM


Title: RE: Computer monitor RFI
Post by: ZENKI on March 14, 2014, 04:16:17 PM
CCFL consumes more power so the inverter will generator more noise.
LED back lighting  generally generates much less RFI. You can however get a crap design with  a poor EMC design that can cause bad QRM.
If you stick with the name brands like Samsung, Philips etc you will be OK. Its all the no name cheap brands that can be danger even it is LED.

The CCFL generates some very strong birdies that can be hard to get rid of. CCFL also seems to have a lot of broadband hash being radiated  from the display and electronics.

LED will be the best long term decision.


Title: RE: Computer monitor RFI
Post by: MW1CFN on June 30, 2017, 02:51:02 AM
I disagree with the recommendation to stick to 'big name brands'. 

I have an LG monitor that produces monumental RFI levels.  It's not the SMPSU, it's the timing ciruitry within the monitor itself.

There is very little that can be done.  You can switch resolution and refresh rates, but this will only shift the location of the RFI, not reduce it.

With a VGA cable, you can make a difference by winding a large air choke of very many turns; I had to use a 10m-long cable on a 5" pipe.  It still didn't really fix the problem to an acceptable level.

Maybe there are some LED screens out there with low or no RFI.  My LG isn't one of them. 

I suspect that the lack of discussion on this problem in general indicates that many are operating in high-RFI environments, such that the screen RFI is low in comparison to that which already exists.  Certainly, the S/N reports one gets when using a good antenna on digital modes does reveal this to be the case for the majority.



Title: RE: Computer monitor RFI
Post by: KC1BMD on September 05, 2017, 05:00:46 AM
I second the comment about name brands not being immune. I had a Samsung SyncMaster 220HD LCD that would turn itself on and off intermittently when transmitting on various HF bands. It had a capacitive touch on/off switch/circuit that would have required major disassembly to access, if a solution even existed (e.g. adding better circuit shileding). I substituted it with an HP ZR2440w LCD which is a really nice display for the money but it puts out what I would describe as a pure and very periodic tone (maybe 1 KHz wide every ~6KHz or so on 40m). I heard it on 20m also but don't recall now what the period was. I tried wrapping some ferrites on the AC and HDMI cords but I'm guessing it's radiating to my antenna because it's so close to my operating position (2nd floor shack with attic center-fed fan dipole with current balun). Interesting the Samsung emitted no such RFI.


Title: RE: Computer monitor RFI
Post by: KC1BMD on September 12, 2017, 05:50:24 PM
Anyone else experience RFI from e.g. HP LED display, similar to what I describe above? At first I thought it was a CW key down by someone tuning (which is what it sounded like) but I quickly realized that was not the case. Any possible solutions I could try besides ferrites on the AC and video cables which didn't seem to help? Somehow I think it's just emission from the display directly to my rigs (which are only only 2-3' away).


Title: RE: Computer monitor RFI
Post by: N3QE on September 13, 2017, 02:32:40 AM
I second the comment about name brands not being immune. I had a Samsung SyncMaster 220HD LCD that would turn itself on and off intermittently when transmitting on various HF bands. It had a capacitive touch on/off switch/circuit that would have required major disassembly to access, if a solution even existed (e.g. adding better circuit shileding).

I have that issue with my Samsung LCD monitor too.