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#81
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Coincidentally, I discovered that one of my RF noise problems, in
addition to this location being an RF nightmare, was one of my PCs. The dern thing splatters RF all over the place even when turned off, I have to pull the plug to get it off the air, so I guess the power supply is going out. Fortunately it's not the server.[/quote] It is the switch mode PS that generates lots of RFI, wether the PC is on of off. Not unusual at all. I found similar problems while testing some of my experimental AF amps in the past. Cheers, John |
#82
Posted to rec.audio.tubes
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"Beam Me Up, Scotty" (Beamus) AM Transmitter -- first prototype
On Sat, 14 Jul 2012 09:45:27 +0000, John L Stewart
wrote: Coincidentally, I discovered that one of my RF noise problems, in addition to this location being an RF nightmare, was one of my PCs. The dern thing splatters RF all over the place even when turned off, I have to pull the plug to get it off the air, so I guess the power supply is going out. Fortunately it's not the server. It is the switch mode PS that generates lots of RFI, wether the PC is on of off. Not unusual at all. I found similar problems while testing some of my experimental AF amps in the past. Cheers, John I frequently have to carry out RF approvals work on products, and this is the situation I have found. PC power supplies get designed, for the most part, quite well, following the chip manufacturer's application note. The power supply is then given its EMC approval. After that, knowing that the thing will never be looked at again, half the suppression components are removed from the PCB. Take the lid off yours and see how many bits are not fitted. The best thing you can do is go into the after-market and find a decent replacement. d |
#83
Posted to rec.audio.tubes
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"Beam Me Up, Scotty" (Beamus) AM Transmitter -- first prototype
On Sat, 14 Jul 2012 09:45:27 +0000, John L Stewart
wrote: Coincidentally, I discovered that one of my RF noise problems, in addition to this location being an RF nightmare, was one of my PCs. The dern thing splatters RF all over the place even when turned off, I have to pull the plug to get it off the air, so I guess the power supply is going out. Fortunately it's not the server. It is the switch mode PS that generates lots of RFI, wether the PC is on of off. Not unusual at all. I found similar problems while testing some of my experimental AF amps in the past. Cheers, John Thanks. Yes, I know its the switching power supply. That's why I speculated it was going out. I've got a dozen PCs here and that's the only one doing it but I don't really know when it 'started' because its reserved for testing things and doesn't always have even the power cord connected since that's 'shared', along the monitor, keyboard, mouse, et all, with another one I also use for testing (one is Windows 7 and the other Windows XP). I mentioned it because I imagine there might still be people who think 'off' really means 'off' but that hasn't been the case ever since the 'soft' power button. It took me a while to pin that particular noise to the PC because noise here is sometimes so bad I can barely receive even the strongest local stations and I know that's nothing in the house because I've tripped the main breaker and had the power company out. They seemed 'surprised' there was so much noise, and confirmed its coming in on their lines, but then informed me the power company is only obligated to provide 'power' and not 'noise free' power. |
#84
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Quote:
Good Luck, John |
#85
Posted to rec.audio.tubes
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"Beam Me Up, Scotty" (Beamus) AM Transmitter -- first prototype
On Sun, 15 Jul 2012 13:22:58 +0000, John L Stewart
wrote: flipper;959374 Wrote: On Sat, 14 Jul 2012 09:45:27 +0000, John L Stewart wrote: - Coincidentally, I discovered that one of my RF noise problems, in addition to this location being an RF nightmare, was one of my PCs. The dern thing splatters RF all over the place even when turned off, I have to pull the plug to get it off the air, so I guess the power supply is going out. Fortunately it's not the server. It is the switch mode PS that generates lots of RFI, wether the PC is on of off. Not unusual at all. I found similar problems while testing some of my experimental AF amps in the past. Cheers, John- Thanks. Yes, I know its the switching power supply. That's why I speculated it was going out. I've got a dozen PCs here and that's the only one doing it but I don't really know when it 'started' because its reserved for testing things and doesn't always have even the power cord connected since that's 'shared', along the monitor, keyboard, mouse, et all, with another one I also use for testing (one is Windows 7 and the other Windows XP). I mentioned it because I imagine there might still be people who think 'off' really means 'off' but that hasn't been the case ever since the 'soft' power button. It took me a while to pin that particular noise to the PC because noise here is sometimes so bad I can barely receive even the strongest local stations and I know that's nothing in the house because I've tripped the main breaker and had the power company out. They seemed 'surprised' there was so much noise, and confirmed its coming in on their lines, but then informed me the power company is only obligated to provide 'power' and not 'noise free' power. Another common & obvious nusance is the CRT type display. Generates a beautiful comb spectrum that can really get in the way as we try to chase down some kinds of problems. Good Luck, John Yes, good point, and I do have a few CRT monitors left but they're just occasionally powered up to do maintenance on a few machines and are off 95% of the time. The rest are LCD but then the switching power supply 'soft power' switch issue potentially crops up again, not to mention the plethora of 'low power' switchers running everything from routers to cell phone chargers. Fact is, RF is never safe in this 'digital world' Amusingly enough, the first 'humongous noise' problem I had, way back in the 'olden days', was a defective doorbell transformer. That's why, for the 'acid test', I killed the main breaker because, funny as it may sound, it's not a trivial task these days to track down everything electrical/electronic. It's worse than an Easter egg hunt and just when you think you've got them all, oh yeah, there's a clock in the oven rolling eyes (or a doorbell transformer). It's just a heck of a lot simpler to flip the mains. Of course, if that does kill the noise it's in the house so then you can flip off all the branches, bring the mains up, and reconnect branch by branch to isolate in which section the culprit lives. That doesn't do me any good when its coming in from the power company but, fortunately, whoever it is 'out there' that's causing the noise doesn't seem to be active of late. |
#86
Posted to rec.audio.tubes
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"Beam Me Up, Scotty" (Beamus) AM Transmitter -- first prototype
On Jul 16, 2:57*pm, flipper wrote:
On Sun, 15 Jul 2012 13:22:58 +0000, John L Stewart wrote: flipper;959374 Wrote: On Sat, 14 Jul 2012 09:45:27 +0000, John L Stewart wrote: - Coincidentally, I discovered that one of my RF noise problems, in addition to this location being an RF nightmare, was one of my PCs. The dern thing splatters RF all over the place even when turned off, I have to pull the plug to get it off the air, so I guess the power supply is going out. Fortunately it's not the server. It is the switch mode PS that generates lots of RFI, wether the PC is on of off. Not unusual at all. I found similar problems while testing some of my experimental AF amps in the past. Cheers, John- Thanks. Yes, I know its the switching power supply. That's why I speculated it was going out. I've got a dozen PCs here and that's the only one doing it but I don't really know when it 'started' because its reserved for testing things and doesn't always have even the power cord connected since that's 'shared', along the monitor, keyboard, mouse, et all, with another one I also use for testing (one is Windows 7 and the other Windows XP). I mentioned it because I imagine there might still be people who think 'off' really means 'off' but that hasn't been the case ever since the 'soft' power button. It took me a while to pin that particular noise to the PC because noise here is sometimes so bad I can barely receive even the strongest local stations and I know that's nothing in the house because I've tripped the main breaker and had the power company out. They seemed 'surprised' there was so much noise, and confirmed its coming in on their lines, but then informed me the power company is only obligated to provide 'power' and not 'noise free' power. Another common & obvious nusance is the CRT type display. Generates a beautiful comb spectrum that can really get in the way as we try to chase down some kinds of problems. Good Luck, John Yes, good point, and I do have a few CRT monitors left but they're just occasionally powered up to do maintenance on a few machines and are off 95% of the time. The rest are LCD but then the switching power supply 'soft power' switch issue potentially crops up again, not to mention the plethora of 'low power' switchers running everything from routers to cell phone chargers. Fact is, RF is never safe in this 'digital world' Amusingly enough, the first 'humongous noise' problem I had, way back in the 'olden days', was a defective doorbell transformer. That's why, for the 'acid test', I killed the main breaker because, funny as it may sound, it's not a trivial task these days to track down everything electrical/electronic. It's worse than an Easter egg hunt and just when you think you've got them all, oh yeah, there's a clock in the oven rolling eyes (or a doorbell transformer). It's just a heck of a lot simpler to flip the mains. Of course, if that does kill the noise it's in the house so then you can flip off all the branches, bring the mains up, and reconnect branch by branch to isolate in which section the culprit lives. That doesn't do me any good when its coming in from the power company but, fortunately, whoever it is 'out there' that's causing the noise doesn't seem to be active of late.- Hide quoted text - - Show quoted text - Gee, and I thought I had bad problems with RFI from 101 gadgets. Mains here are filthy with noise, but probably most is RF pick up because the mains street wiring acts as a vast antenna network. The source impedance of the noise is low, so just putting 0.01uF across active and neutral may not do much. RF noise comes in via common mode and differential mode, and one way to stop mains noise is to put bigger value caps across active to neutral, and between both active neutral to an earth stake or water pipe, and still you'd find noise. Earth paths have impedance and copper pipes buried in the ground under a house probably offer a good earth but one that still has impedance. So when a radio is also well earthed to the same water pipes, its all floating on the same earth signal as the mains, but the impedance of the earthing may not be linear, and could be diode like, and so you get rectified RF waves applied to the receiver and hum in the audio signal. I have aluminium foil insulation under my roof tiles, and I put it there before knowing it could seriously affect radio reception. It acts as a large capacitor plate that isn't earthed, and even if I did earth it, the wire used acts like a coil and there's a resonant CL circuit. And maybe slight aluminium oxide also is a bit diode like. To try to fully understand what causes noise in terms of the equivalent LCR model for the mains, earth and insulation would be pointless - too complex. I should live in a house without foil insulation and with no known noisy gadgets, be like the Amish, no electricity. I have tried putting my AM set inside a steel box with careful mains input filtering but then the ferrite rod doesn't work very well. Maybe an aluminium box would be better, or use bronze fly wire. So, my favorite AM station has hum if I use a bit-of-wire antenna. But if I use a ferrite rod the noise is 30dB less, and tolerable, although some days hum will just switch on when something unknown begins to cause it. Probably my best way of getting good AM would be to live 15km away on the far side of the radio stations and in a farm house with hardly any other people around, and few ppl between the farm house and stations. But I can't afford just move. I could maybe rent a farm house and rent out my house to someone who paid more than farm house rent, but all too much bother for not a huge problem. I don't have an oven with electronic clock, don't have a phone answering gadget, and don't have so many things. I did once have a Shimasu phone answer gadget, and with a linear supply, and It made terrible noise on AM, and nothing I did would silence it until I just unplugged it, cut its cable, and stuck it the rubbish bin. If people really wanted to phone me they'd better try me later when I am likely to be home. I was getting fed up with returning a call to them and I'd have to leave a message on their answer machine. So for last 10 years, no answer machine, because all those calls at 22c each add up. Patrick Turner. |
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