tag:blogger.com,1999:blog-4774014561040227748.post9028300375489393222..comments2024-03-22T10:42:05.161-06:00Comments on KA7OEI's blog: Completely containing switching power supply RFIUnknownnoreply@blogger.comBlogger12125tag:blogger.com,1999:blog-4774014561040227748.post-73624948887047401212021-12-10T14:54:37.876-07:002021-12-10T14:54:37.876-07:00Where have you been all my life?....or at least th...Where have you been all my life?....or at least the last 5 years, when neighbourhood RFI ended my “radio career”. Thank you for one of the best “hands-on” , real world RFI mitigation website/blog. You have provided the exact type of “homebrew” solutions I have been looking for. I especially appreciate you showing how to gleam the parts from “on-hand” SMPS and electronics. That is especially educational and hope you will do more. <br />Finding the neighbourhood RFI source is just as troubling as getting co-operation from the offender. I would never modify someones offending equipment, but I can at least insure my own home is RFI “clean” and prove “its not me”...here is how it “should”have been designed/built. Joehttps://www.blogger.com/profile/08995516987527086464noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-61192437380273818092020-07-22T10:16:25.630-06:002020-07-22T10:16:25.630-06:00Hi Richard,
As you have (no doubt) found out, swi...Hi Richard,<br /><br />As you have (no doubt) found out, switching off/unplugging all SMPS units (Switch Mode Power Supplies) is the necessary first step in mitigating this problem.<br /><br />One thing that *may* help a little bit is to place ferrite on the leads in/out of the power packs/wall warts - but while this can help, it usually offers 2-3 S-units of improvement, at best - and if you have a "10 over" noise source atop a native S-3 noise floor, you will still end up with a lot of excess noise.<br /><br />* * *<br /><br />The *only* sure ways to completely get rid of the noise are to:<br /><br />- Replace the power supplies with "quiet" ones. In general, linear supplies are quiet, but you can sometimes find known-quiet switch mode supplies: Brands that you may have heard of (Triad, Astec, Delta, etc.) may be better in terms of noise (no guarantee, though) simply because they are less likely to omit the noise suppression components like some of the no-name supplies are wont to do.<br /><br />- Contain them in a box as described on this page. A bit draconian, but effective. If all of your noisy supplies are in one place, you should be able to put them all together: They can share a common mains input, but will require filtering on each DC lead.<br /><br />If you are of the DIY type, putting the power supplies in their own boxes with filtering is likely the more practical solution as finding independent, linear power supplies of the correct voltage and current can be difficult and expensive.<br /><br />Let me know what you do to address this problem.<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-56329209374807159052020-07-04T23:13:34.977-06:002020-07-04T23:13:34.977-06:00Greetings, Clinton. Found your another email in QR...Greetings, Clinton. Found your another email in QRZ.com and asked you some questions. Hope you do not mind that direct approach. This is VK2CRB, Richard.<br />I have a gigantic headache here. I cannot receive almost anything.Bought the MFJ 1026 and when I found the internal antenna would so something, only in 40 M, then I realized the drama is close, inside the house. I have many power packs as I have servers, firewalls, NUC PC's , switches. They appear to re inject back heaps of rubbish to the 240V AC power lines that travel all around the house. I have, sadly, 8 packs and may have to replace them by building linear PS's, perhaps ? What would be your view, thanks and 73'slatinaussierichardhttps://www.blogger.com/profile/05210584703014433325noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-13108733468779926072020-01-15T13:48:56.356-07:002020-01-15T13:48:56.356-07:00If the buzz weren't modulated, it would appear...If the buzz weren't modulated, it would appear as "clean" carriers every 30-60 kHz - getting more unstable as the order of the harmonic increased (e.g. higher RF frequency, more multiplication.)<br /><br />These are typically modulated at twice the line frequency due to the full-wave bridge rectifier on the mains side which results in pulsating DC with 2x mains frequency ripple.<br /><br />It is this varying voltage - and the load of the regulator as it "follows" this ripple - that causes the frequency to shift, usually at twice the mains frequency.<br /><br />It is often the case that these "buzzy" harmonics that occur every 30-60kHz are distinguishable on lower frequencies (say, 4 MHz and lower) but they "smear" together at higher frequencies (14 MHz and up) and are more difficult to spot - particularly when SSB is used: Listening on AM will often reveal that the noise floor itself has 2x mains components.<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-68605494118878361302020-01-15T12:32:48.426-07:002020-01-15T12:32:48.426-07:00Typically, switching power supplies sound like a &...Typically, switching power supplies sound like a "buzz" every 30-60 kHz - the power supply's switching frequency - up and down the bands, usually worse on lower bands, but not always. This buzz is usually modulated at twice the power line frequency.<br /><br />I'm not following this paragraph. How is the buzz, the power supply's switching frequency, being modulated at twice the power line frequency? Dianahttps://www.blogger.com/profile/06962897607368086950noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-65117186813815870252018-09-08T12:46:01.077-06:002018-09-08T12:46:01.077-06:00The best, most-foolproof way to "quiet" ...The best, most-foolproof way to "quiet" an existing power supply is, as this blog post shows, to completely wrap it in another metal chassis with filtering on all inputs and outputs.<br /><br />As it happens, I did another blog post about "cleaning up" a UPS that was producing a lot of RFI - and this post which may be found here:<br /><br />http://ka7oei.blogspot.com/2017/12/containing-rf-noise-from-sine-wave-ups.html<br /><br />I hope that this helps, and I'll be interested in what you come up with.<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-31107744216657583492018-09-07T02:19:49.033-06:002018-09-07T02:19:49.033-06:00Thank you!
-- I want to run home Internet with bat...Thank you!<br />-- I want to run home Internet with battery UPS backup. The backup is 12V sealed lead-acid. The modem, router, and network switch will all run off 12VDC (noisy switched) so I plan to scrap the wall-warts and just run a cleaned, battey-backed, 12VDC supply throughout. <br />--- How should I clean RFI from the APC supply that is tricklle-charging the battery? Or, if I Faraday-cage that, will the battery clean up the power output?<br />--- Many thanks!AlexaPhilhttps://www.blogger.com/profile/15710779283286305022noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-89206027095332113302017-02-22T08:34:29.035-07:002017-02-22T08:34:29.035-07:00I just had a similar problem with this oddball pow...I just had a similar problem with this oddball power supply I was using that consisted of a 5V switching supply driving multiple 5V to +/-9V DC/DC converters. Originally everything was in a plastic case and I moved it to a metal case. For the input I used a Corcom line filter that basically encapsulates your input line filter circuit. I also added monolithic ceramics to all of the +/-9V outputs to the common for each power supply. When I powered it up there was still noise but somewhat reduced. That's when I realized the "common" outputs for each DC/DC converter were ungrounded to the case. After grounding the common of each DC/DC converter, I can detect no noise on nearby shortwave receiver. Thanks for the useful article!Anonymoushttps://www.blogger.com/profile/16893863172276157228noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-40387535505848766402016-02-19T12:32:51.345-07:002016-02-19T12:32:51.345-07:00Hi Robert,
Nice write-up!
In looking at those pi...Hi Robert,<br /><br />Nice write-up!<br /><br />In looking at those pictures I can't immediately spot the series inductor that is commonly installed in series with some of the output capacitors, but I do see what appears to be a bifilar choke on the AC input side - but even with the addition of these components the series reactance is not likely to be high enough to completely quash the radiation of hash: It is reasonable to expect such filtering to reduce hash by 20dB, but that is "only" 3-4 S-unit - and you were seeing far more than that!<br /><br />Alas, the only practical solution to this problem is to install filtering capable of knocking down this energy by 40-60dB and the only way that this can usually be done is to have the input and output filters be capable of shunting HF energy around the device - and the only real way that many of those small, "inline" (with the power cord) supplies can be modified for this is to put them in another box and add filtering similar to that described on this page.<br /><br />Best of luck and let me know if you modify it and how it works out!<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-76136752772430217292016-02-18T06:52:17.700-07:002016-02-18T06:52:17.700-07:00I think I'll look into your "fix" so...I think I'll look into your "fix" sometime. I bought a very cheap 30A SMPS from Banggood.com (less than USD20). I figured it was cheap enough to take a risk. It's OK for my 2 metre FM rig, but it gives S7 noise on the HF SSB! (I did a write-up here, if you don't mind me posting a link: http://www.hamradioforum.net/threads/6662-Switched-mode-PSU-and-SSB-AM?p=28968#post28968)Anonymoushttps://www.blogger.com/profile/18236925671126988497noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-75350285881968559022014-12-24T10:09:57.195-07:002014-12-24T10:09:57.195-07:00Actually I have a rail of Cree, dimmable LED track...Actually I have a rail of Cree, dimmable LED track lights in my ham shack and I don't notice anything at all from them at HF.<br /><br />I do some listening at LF/VLF and there, the dominant source of interference is the dimmer itself, regardless of what sort of lamps I might use, which is why I have an incandescent desk lamp available. For listening at these frequencies I have also modified the LCD monitors to minimize egress of their switching supplies, adding extra reactance to their AC line filters (mostly inductance!) so that I can have them on without causing much problem - something that I could *never* do with the old CRT monitors!<br /><br />I have noticed that with the LED lamps they will clobber 2 meters (146 MHz) but I have to be within a 2-3 feet (a meter) or so of a lamp for it to be an issue, this on a weak signal: Since I have rooftop antennas, this is of no importance.<br /><br />One common problem with LED lights is their use in garage door openers in which they get placed within a few inches of the receiver: Unless one can simply move the receiver a few feet away, this is probably not a good idea, although a friend of mine simply swapped the position of a CFL and LED lamp in his operator and the small bit of extra distance seemed to solve the problem!<br /><br />While I don't have a lot of LED lighting in my house, what I do have is a known brand (Cree) from one of the "big box" home improvement stores that I picked up on sale, so I am quite sure that they are not counterfeit units.<br /><br />Having seen some if the really cheap imports that completely lack EMI/RFI filtering on the AC inputs - and also on the outputs, which is important if the LED is somewhat long and linear (e.g. a string of lights to act as an antenna) I have little doubt that they could and would cause terrible interference! From a purely technical standpoint, that sort of thing is fairly easy to fix, and from a practical standpoint, those cheap LED lamps probably won't survive very long, anyway - probably due to sub-standard components (e.g. capacitors!) and won't be a source of interference for a terribly long time, anyway!<br />KA7OEIhttps://www.blogger.com/profile/01153508130273704727noreply@blogger.comtag:blogger.com,1999:blog-4774014561040227748.post-56436049300869003192014-12-23T19:09:02.321-07:002014-12-23T19:09:02.321-07:00Hmmmm... my guess that you can't use LED light...Hmmmm... my guess that you can't use LED lighting at your home then (especially el-cheapo one), they emit lots and lots of EMI. What's your experience?Rusdyhttps://www.blogger.com/profile/16495723463078718309noreply@blogger.com