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Interference on Radio when recording to plugged in laptop
In article .com,
"bradvk2qq" wrote: Mike Chambers wrote: Unfortunately that didn't solve the problem. The transformer should have fixed the problem. The noise is most likely coming from the laptop switched-mode power supply. Have you tested it while running on batteries alone? I have several radios connected to computers, and for this I use the Buxcomm Rascal GLX (www.buxcomm.com) and this works for both of my pc's and my laptop. The Rascal is also available as a kit for transceivers and you can build just the receive side if you wish. That said, the transformer alone should be enough, and there is the possibility that you did not assemble the cable shielding correctly or add sufficient bypassing. My computers receive audio, decode it and post it to my webpage. This system does work, do not despair. Most likely the switching noise from the laptop passes through the connecting cable as common mode noise. Try RF chokes on the cable on both ends. -- Telamon Ventura, California |
Interference on Radio when recording to plugged in laptop
In article ,
John Smith I wrote: Mike Chambers wrote: ... Mike: Here is an interesting link: http://www.waypoint.com/users/~disco...esentation.htm One circuit I seen on this page makes use of an opto-isolator. Seems to me that with a led and photo-transistor one could kludge together a unit which would seem to perform miracles!!! The OP already tried a isolation transformer so I don't think an opto-isolator will be any more helpful. I expect that it is a common mode noise issue. He can buy common mode chokes that just clamp on the cables to find out. -- Telamon Ventura, California |
Interference on Radio when recording to plugged in laptop
Telamon wrote:
... The OP already tried a isolation transformer so I don't think an opto-isolator will be any more helpful. I expect that it is a common mode noise issue. He can buy common mode chokes that just clamp on the cables to find out. Surely you jest, with optical isolation, there is NO direct connection ... Unless you are proposing the rf is able to transverse the light beam. JS |
Interference on Radio when recording to plugged in laptop
John Smith I wrote: Surely you jest, with optical isolation, there is NO direct connection ... Unless you are proposing the rf is able to transverse the light beam. JS The optoisolators are only used for ptt keying, not for the audio. The audio is usually isolated with transformers. But, just because the op has tried transformers, doesn't necessarily mean he did it correctly. Brad. |
Interference on Radio when recording to plugged in laptop
On Wed, 03 Jan 2007 16:02:14 -0800, Mike Chambers
wrote: I have an Eton E5 which I connect to my laptop via the Line Out on the Eton to the Line In on the laptop. This works great for recording shortwave broadcasts, but if the laptop is plugged in, it generates some interference on the radio (only when they are connected via lineout / in). If I unplug the laptop, there is no interference. Does anyone know if there is anything I can do to get rid of the inteference? I want to set up my machine to record programs overnight, so I can't leave the laptop unplugged. mike http://mesh.typepad.com Is your laptop battery weak where it is always charging? This would overheat the supply and generate more rfi. We had a Dell with this problem at work. We used to plug the power supply into a 110 volt isolation transformer and then we connected a ground lead to the ground side of the speaker jack on the computer. Another alternative is to replace the laptop power supply with another brand which hopefully will not be as noisy. Jim |
Interference on Radio when recording to plugged in laptop
Telamon wrote:
... Either one will not be an effective block unless they are designed to prevent passing common mode RF noise. It takes very little in stray capacitance or mutual inductance to go around the opto-isolator. If you are an electronics engineer, I'd venture you are a damn poor one. The opto-isolation I proposed would be about 10,000x more isolation than an audio xfmr. Coupling of rf noise though the audio xfmr is just a question of "how much?" Indeed, I'd be surprised if they even provided proper shielding (grounded metal sheet over inner winding with ends of sheet insulated from each other) of one winding from another! If the core material is ferrite, like in the cheap china junk, I'd throw it away for such uses. Silicate-steel laminations might be usable when rf is a problem ... Regards, JS |
Interference on Radio when recording to plugged in laptop
In article ,
John Smith I wrote: Telamon wrote: ... Either one will not be an effective block unless they are designed to prevent passing common mode RF noise. It takes very little in stray capacitance or mutual inductance to go around the opto-isolator. If you are an electronics engineer, I'd venture you are a damn poor one. The opto-isolation I proposed would be about 10,000x more isolation than an audio xfmr. Coupling of rf noise though the audio xfmr is just a question of "how much?" Indeed, I'd be surprised if they even provided proper shielding (grounded metal sheet over inner winding with ends of sheet insulated from each other) of one winding from another! If the core material is ferrite, like in the cheap china junk, I'd throw it away for such uses. Silicate-steel laminations might be usable when rf is a problem ... You are very weird and you have poor comprehension. Go back and re-read the thread and you will find that I did not recommend the transformer. My post of a few lines stated that the opto-isolator would be not any better than the transformer. I don't know where you get your ideas from but you are one very confused individual. The reason another poster thought the transformer would help is because the problem was created by a ground loop. If the problem was a ground loop the transformer or opto-isolator would help. My thinking was always that it was a common mode noise problem with the switching noise from the laptop getting to the radio through the connecting cable. A ferrite clamp on core is a good solution. Ferrous metals are much lower in inductance value than the ferrite and would not work as well for a similar size core. Why do you bother to post if you have no idea what you are talking about? -- Telamon Ventura, California |
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Interference on Radio when recording to plugged in laptop
Telamon wrote:
... In your previous post: --------------------------------------------------------------------- "I usually don't joke about the subject. The transformer is really no different than the opto-isolator for DC isolation. One couples primary and secondary circuits magnetically and the other with photons. Either one will not be an effective block unless they are designed to prevent passing common mode RF noise. It takes very little in stray capacitance or mutual inductance to go around the opto-isolator." --------------------------------------------------------------------- See the part, "The transformer is really no different than the opto-isolator for DC isolation. One couples primary and secondary circuits magnetically and the other with photons." Why in the hell would we even concern ourselves with dc isolation, it is rf which is causing the problem ... Now, see the part, "Either one will not be an effective block unless they are designed to prevent passing common mode RF noise." There would be NO coupling, other than a light beam--and I asked you, are you claiming the rf is traversing the light beam? (and, if so, you will notice that I implied ONLY AN idiot would site that as being a problem in this case.) Optical isolation would be an ABSOLUTE cure for his problem. JS |
Interference on Radio when recording to plugged in laptop
Mike,
I had the same issue, and when I first attempted it I clamped it straight ono the cable and still had noise "BUGGER!!". This is when I read some where to coil the cable to form 3 loops / turns about 3-4 fingers wide and I clamped two ferrite cores from RS. That did the trick and the noise is 100% gone. Hope that helps. Regards Mark Mike Chambers wrote: Thanks. That didnt seem to help any. mike On Thu, 04 Jan 2007 10:47:45 +0100, Charly wrote: Hello, you can also get some noise-reduction ferrite core, such as this : http://www.shinemicro.com/images/ferritethumb.jpg Perhaps you have some already clamped on some device's wire (digital camera, AC/DC tranformer, modem, etc...). If you can un-clamp one a clamp it on your laptop power wire OR audio line wire, just check if it helps... I did that on my AC/DC adapter of my SW radio, and it helps reducing (a little) incomming RFI. Charly |
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