LCD TV Causing RFI
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Hi,
I have a Samsung 46" LCD TV that is causing RFI on the 20m PSK calling freq (14.070). My station setup is a K2 powered by an Alinco DM-330 switcher. The interference shows up in the waterfall display; it's about 1000 Hz wide right on 14.070 (the coincidence is weird), doesn't move, and doesn't show up anywhere else that I've found thus far. It's not overwhelming; I can still decode signals through it. It vanishes as soon as the TV is turned off. The offending TV is not close to the shack: TV is on the first floor, shack on the second floor (on the opposite side of the house), antenna in the attic. The TV is using cable with a DVR. It's one of those things that I "can live with," but would prefer solving the problem. The TV was purchased in Feb 2009, so it's too old to return, too new to replace. As always, thanks for any suggestions. N5BCN - Brian |
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Hi Brian,
Try #31 ferrite clamp ons on on leads coming from the TV starting with the power cord. They can be found in small quantities here: http://www.mouser.com/catalog/catalogUSD/642/952.pdf The 0.51" and 0.72" ID ones will allow several turn through which is usually necessary. The 0.72 one is huge and heavy but works well. AB2TC - Knut
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In reply to this post by Brian - N5BCN
On 1/29/2011 9:40 PM, Brian - N5BCN wrote:
> The offending TV is not close to the shack: TV is on the first floor, shack > on the second floor (on the opposite side of the house), antenna in the > attic. REPEAT AFTER ME -- IT DOESN'T MATTER WHERE THE SHACK IS, IT'S THE ANTENNAS! Whatever trash the TV is generating is conducted from the TV to the CABLES that are connected to it -- power, antenna (or CATV), DVR, audio -- and RADIATED by those cables to your ham ANTENNAS. It can also be radiated directly from wiring inside the TV if it is poorly shielded, or poorly designed. > The TV is using cable with a DVR. RF trash radiated by the CABLES can be killed by winding multiple turns of each cable through it's own #31 ferrite core. Ferrite cores come in many sizes to fit cables of various sizes, and to allow the needed number of turns. You'll need about 5 turns through a core to optimize the suppression on 20M, and that suppression will be pretty effective from at least 40M up to 10M. The #31 material is made only by Fair-Rite, an excellent US company that makes the vast majority of ferrite materials used by hams. For a tutorial discussion of all this, and specific recommendations for parts to buy and how to wind the chokes, see http://audiosystemsgroup.com/RFI-Ham.pdf FWIW -- it is VERY rare for LCD TVs to cause RFI to ham gear, and the major Korean brands have a pretty good reputation in that regard. This is only the second report I've seen, and RFI is one of my specialties. :) Please let us know the exact model number so that we can post it to the RFI email reflector. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Thanks to everyone's suggestions, I'm zeroing in on the culprit!!!
For reference, the two TVs in my house with the issues: Samsung 46" LCD Model LN46A580P6F Samsung 40" LCD Model LN40A530P1F (we rarely use this one, that's why I didn't discover the RFI on this one until recently) I had subconsciously convinced myself that it must be a noisy power supply in the TV, but it turns out this wasn't the case at all!! There are only two wires connected to each TV: A/C power and a HDMI cable to the DVR (cable is plugged into the DVR, not the TV). The DVR is always "on" to record show when the TV is off. With the TV on, I unplugged the HDMI cable and viola!, no RFI. So, it seems the noise is emanating form the HDMI cable, either being generated by the TV or the DVR, but ONLY WHEN the TV is on! I have some #31 ferrite cores on order from Mouser, and the offending HDMI cable will be the first target. I'm secretly hoping it's the DVR box, and not my TV, so I can blame the cable company. ;-) Not sure how to isolate which one it is, though. 73 N5BCN - Brian |
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On 1/30/2011 3:19 PM, Brian - N5BCN wrote:
> There are only two wires connected to each TV: A/C power and a HDMI cable to > the DVR (cable is plugged into the DVR, not the TV). The DVR is always "on" > to record show when the TV is off. > > With the TV on, I unplugged the HDMI cable and viola!, no RFI. So, it seems > the noise is emanating form the HDMI cable, either being generated by the TV > or the DVR, but ONLY WHEN the TV is on! You left out what may be the most important cable(s) -- the coax that provides the RF signal to these sets (and/or a CATV box or DVR). That cable can also be the antenna, and the HDMI cable may simply be coupling the RFI from the set to that coax. Now, a choke on that HDMI cable may solve the problem, but don't forget that the coax is there, and could be radiating other lower level trash from those other boxes that you haven't identified. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Brian - N5BCN
Brian,
Please keep us posted when you zero in on the culprit. I had a similar RFI issue with one of our DirecTV boxes. I narrowed down to the RG6 coax feeding the box. I added one ferrite choke to the cable right where it connected to the box and less RFI, added two more and voila, no more noise ! RFI mitigation is almost a science in itself. My primary reference and one I recommend highly for understanding and solving RFI issues is "A Ham's Guide to RFI" on line provided by Jim Brown, K9YC. The web page is http://www.audiosystemsgroup.com/RFI-Ham.pdf Bob K6UJ On Jan 30, 2011, at 3:19 PM, Brian - N5BCN wrote: > > Thanks to everyone's suggestions, I'm zeroing in on the culprit!!! > > For reference, the two TVs in my house with the issues: > Samsung 46" LCD Model LN46A580P6F > Samsung 40" LCD Model LN40A530P1F (we rarely use this one, that's why I > didn't discover the RFI on this one until recently) > > I had subconsciously convinced myself that it must be a noisy power supply > in the TV, but it turns out this wasn't the case at all!! > > There are only two wires connected to each TV: A/C power and a HDMI cable to > the DVR (cable is plugged into the DVR, not the TV). The DVR is always "on" > to record show when the TV is off. > > With the TV on, I unplugged the HDMI cable and viola!, no RFI. So, it seems > the noise is emanating form the HDMI cable, either being generated by the TV > or the DVR, but ONLY WHEN the TV is on! I have some #31 ferrite cores on > order from Mouser, and the offending HDMI cable will be the first target. > > I'm secretly hoping it's the DVR box, and not my TV, so I can blame the > cable company. ;-) Not sure how to isolate which one it is, though. > > 73 > > N5BCN - Brian > > ----- > K2 #6800 KSB2 KAT2 KIO2 K160RX KNB2 > -- > View this message in context: http://elecraft.365791.n2.nabble.com/LCD-TV-Causing-RFI-tp5973980p5975705.html > Sent from the [HAM] mailing list archive at Nabble.com. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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More interesting findings:
I disconnected the coax cable to the DVR: RFI is still there! So the cable coax+DVR does not seem to be the source of my RFI on 20m. With the coax cable disconnected, but the DVR still connected to the TV via HDMI cable, the RFI is there if I'm playing a recorded show to the TV (in other words, data on the cable), but vanishes (no RFI) when I "stop" the DVR (no data being sent to the TV). In both scenarios, the TV is on, coax cable disconnected. This suggests to me that the source is indeed the DVR and it's generating RFI on the HDMI cable. BTW, my cable service is Time Warner Cable (TWC), the DVR is a Samsung provided by TWC. 73 N5BCN - Brian |
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On 1/30/2011 5:34 PM, Brian - N5BCN wrote:
> This suggests to me that the source is indeed the DVR and > it's generating RFI on the HDMI cable. The possibilities are more complex than that -- it could still be the signal from DVR is causing the TV to generate the trash. From your description, it does sound like the coax is not involved. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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This post was updated on .
In reply to this post by Brian - N5BCN
FYI, a follow up to my RFI hunting adventure:
I ordered a bunch of ferrite cores from Mouser, Part #623-0431176451, at about $7.00 each. They have a 0.72 inch inner diameter. The offending HDMI cables are fairly thick; I could only manage two complete turns and still be able to snap the core shut. Three turns and I had to zip-tie the core shut. The cores helped immensely. I achieved the best results with one core with three turns and a second core added to the cable with two turns, both on the DVR end of the cable. The RFI has been abated about 95%. Question: does the tightness of the coils going through the core have any affect on the impedance? Thanks for everyone's help on this issue!! N5BCN - Brian |
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On 2/8/2011 7:30 AM, Brian - N5BCN wrote:
> FYI, a follow up to my RFI hunting adventure: > > I ordered a bunch of ferrite cores from Mouser, Part #623-0431176451, at > about $7.00 each. They have a 0.72 inch inner diameter. > > The offending HDMI cables are fairly thick; I could only manage two complete > turns and still be able to snap the core shut. Three turns and I had to > zip-tie the core shut. That's why I recommend the larger 1-in i.d. clamp-on. They cost more, but you could have solved your problem with one core having more turns. > The cores helped immensely. I achieved the best results with one core with > three turns and a second core added to the cable with two turns, both on the > DVR end of the cable. The RFI has been abated about 95%. > > Question: does the tightest of the coils going through the core have any > affect on the impedance? Not enough to matter. What WOULD help in your application would be to bunch the turns tightly together so that there is more capacitance between turns, which would lower the resonant frequency. The reason that you needed two cores is that the resonant frequency of your chokes is far too high. Study http://audiosystemsgroup.com/RFI-Ham.pdf to understand this. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Skimping on suppression core cost is fully eschewed. Don't go there, spend
the bucks, get the right stuff. The suppression below self resonance increases with the SQUARE of the turns through the center. That is to say that a pair of three turn suppressors is worth 18, and a single five turn is 25, all else held equal. Even if the five turn core costs DOUBLE the three turn job, it's STILL cheaper bang for the buck. And if you just HAVE to use two cores to feel good, it's 50 vs 18. LEARN the stuff on Jim's web page. Save yourselves grief and financial mismanagement. 73, Guy. On Tue, Feb 8, 2011 at 1:11 PM, Jim Brown <[hidden email]> wrote: > On 2/8/2011 7:30 AM, Brian - N5BCN wrote: > > FYI, a follow up to my RFI hunting adventure: > > > > I ordered a bunch of ferrite cores from Mouser, Part #623-0431176451, at > > about $7.00 each. They have a 0.72 inch inner diameter. > > > > The offending HDMI cables are fairly thick; I could only manage two > complete > > turns and still be able to snap the core shut. Three turns and I had to > > zip-tie the core shut. > > That's why I recommend the larger 1-in i.d. clamp-on. They cost more, > but you could have solved your problem with one core having more turns. > > The cores helped immensely. I achieved the best results with one core > with > > three turns and a second core added to the cable with two turns, both on > the > > DVR end of the cable. The RFI has been abated about 95%. > > > > Question: does the tightest of the coils going through the core have any > > affect on the impedance? > > Not enough to matter. What WOULD help in your application would be to > bunch the turns tightly together so that there is more capacitance > between turns, which would lower the resonant frequency. The reason > that you needed two cores is that the resonant frequency of your chokes > is far too high. Study http://audiosystemsgroup.com/RFI-Ham.pdf to > understand this. > > 73, Jim Brown K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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On 2/8/2011 12:20 PM, Guy Olinger K2AV wrote:
> That is to say that a pair of three turn suppressors is worth 18, and > a single five turn is 25, all else held equal. Another important point. With any ferrite used for suppression, RESONANCE is the SWEET spot, and any ferrite that's GOOD for suppression will yield a VERY low circuit Q. Values on the order of 0.5 are typical for Fair-Rite #31 and #43. That means the resonance will be VERY broad (typically covering a frequency ratio of 3:1 or 4:1 for decent suppression, and up to 8:1 for #31 below 5 MHz). 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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