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Old 14-03-2011, 06:39   #1
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Picking Up Some RF Noise from ASUS Netbook Charger

I've got one of those little ASUS IEEE netbooks. It works fine for my purpose but since I use it to control my SSB (ICOM M710-RT) I noticed that when I plug it in either to AC or DC then my SSB starts picking up quite some noise (even in the case the netbook is not wired to the radio at all).

I even tried to power it with a DC plug using a totally separate battery bank but I keep picking up the same noise which is not there when I run it on its internall battery only.

It must be the AC transformer (when I charge it from AC) or the DC converter when I plug it into the lighter socket. When the power cord is not connected to the netbook the radio picks up no RF noise but I would think it stands to reason since neither transformer/converter have any load connected.
As soon as I plug it in into the netbook then there it is!

Any idea? Also the stereo is picking up some of the noise.
How can I try to reduce it?

Thanks
Scud
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Old 14-03-2011, 06:49   #2
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Re: picking up some RF noise from ASUS netbook charger

I have similar problem. Have found that the converter must be turned off when uploading weatherfax or email or for using the SSB at all. It produces lots of RF interference. I have a small pure sine wave converter just large enough to recharge computers, plotters, and things with wall-warts. I know very little about radio electronics and would be interested in hearing from people who know more about how to remedy this. Is it possible to put RF filters on the converter? Some sort of housing shield? The filters on all the SSB cables do not keep this signal out.
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Old 14-03-2011, 07:41   #3
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Re: picking up some RF noise from ASUS netbook charger

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Originally Posted by smurphny View Post
I have similar problem. Have found that the converter must be turned off when uploading weatherfax or email or for using the SSB at all. It produces lots of RF interference. I have a small pure sine wave converter just large enough to recharge computers, plotters, and things with wall-warts. I know very little about radio electronics and would be interested in hearing from people who know more about how to remedy this. Is it possible to put RF filters on the converter? Some sort of housing shield? The filters on all the SSB cables do not keep this signal out.
Actually I don't even try using the sine-wave converter. I pick up the noise even running on AC shore power or using the charger that I bought at bestbuy that plugs directly into DC power outlet.

Scud
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Old 14-03-2011, 08:47   #4
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Re: picking up some RF noise from ASUS netbook charger

Would be nice to hear from some people with some technical experience with these issues. I know that RF interference can come from all kinds of sources. Have done some music recording and have often picked up signals from weird places. It seems that anything can act as an "antenna" and pick up frequencies from remote radios, tools, appliances, and anything that puts electronic wavelengths into the air. Once had a track mysteriously pick up Japanese speaking short wave signals coming in through an electronic keyboard! There are probably hundreds of possible interference sources around a busy dock. The interference I get on the SSB/Pactor/computer does not come in through power cords because when charge cords are disconnected, as soon as I turn the converter on, the signal becomes essentially unreadable. Interference is either airborne or coming in through house battery side(to which the converter and SSB are both attached).
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Old 14-03-2011, 10:01   #5
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Re: picking up some RF noise from ASUS netbook charger

It is probably the DC-DC switching convertor inside the eeePC generating the RFI, and any cables attached to the computer may act as antennas to transmit that RFI. Since your boat's antenna is so close to your operating position, that is probably where you are picking up the interference.

You might see about getting some mix 31 ferrites to put on those cables as close to the computer as possible. Get a size that will let you put several wraps of cable through the ferrite - effectiveness increases as the square of the number of wraps. It may be you will need to isolate the positive power lead and wrap it alone through the ferrite to get proper suppression. You can only try!
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Old 14-03-2011, 12:46   #6
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Re: Picking Up Some RF Noise from ASUS Netbook Charger

Hmm. I have one of these as well. Will have to see if this is an issue, which it may not be because the tuner will be behind a steel bulkhead and the ASUS will be Velcro'd down as a plotter in the steel sided pilothouse.
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Old 15-03-2011, 07:15   #7
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Re: picking up some RF noise from ASUS netbook charger

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Originally Posted by SoonerSailor View Post
It is probably the DC-DC switching convertor inside the eeePC generating the RFI, and any cables attached to the computer may act as antennas to transmit that RFI. Since your boat's antenna is so close to your operating position, that is probably where you are picking up the interference.

You might see about getting some mix 31 ferrites to put on those cables as close to the computer as possible. Get a size that will let you put several wraps of cable through the ferrite - effectiveness increases as the square of the number of wraps. It may be you will need to isolate the positive power lead and wrap it alone through the ferrite to get proper suppression. You can only try!
Thank you! I'll try the mix 31 ferrite. I actually made your same guess.
I hope that working on the power cord may ease the issue.

Scud
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Old 15-03-2011, 08:26   #8
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Re: Picking Up Some RF Noise from ASUS Netbook Charger

You should isolate the source of the noise.
Both powersuplies, DC/DC and Shore have high current oscillators at about 1 MHz inside.
Give a try to put the converter into a box out of tin/iron.
That will shield the magnetic and electric field.

When you work with the intenal battery (no external converters) and the noise is still there, then its the internal DC converter inside the notebook.
Ferrite in the cable might help, I am afraid not.
Its the radiation of the internal oscillator emitting directly to the air and antenna.

Or try if another notebook with a shielding metal case (aluminium) is producing also noise.
If thats the case, have a look at your radio equipment grounding.
Wilhelm
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