power supply interference with radio broadcast

Renton Maclachlan · July 10th, 2011, 05:10 PM

Thanks Greg,

I don't know anything about electrics and electronics and so there is no way I could build something (even though I am more than a tinkerer and make stuff all the time!).

I've just had a long talk to a helpful guy in a local electronics store exploring an idea suggested to me of using a computer psu (which I have) which he says will have the metal cage its in, earthed and so removing the RF. Just need to get a connector from the psu to usb to enable me to try this.

Firstly however I will try powering the ipod through my laptop to see if I'm going in the right direction.

Greg Miller · July 10th, 2011, 05:48 PM

I certainly don't want to discourage your experiments there, and I encourage you to do on in some direction... don't give up because a solution is possible.

I would just mention that as soon as the wires exit the computer supply's individual metal box, they can act as antennas. If the circuitry is generating any RF noise, it can sneak out on those wires, and radiate from there.

This normally isn't too much of a problem, because all the wiring is normally enclosed within another big metal box... the case of the computer itself.

But if you are going to have those wires hanging out, connected to a USB connector, you might need to put ferrite beads on some or all of those wires to reduce the RF radiation.

Also, a computer supply generates several different voltages: +5, +12, -12 at the minimum. I have heard (though have not discovered on my own) that the supply needs some finite electrical load on each of those buses, or else it may not operate correctly. The last thing you want is for the supply to lose its regulation, "run wild," and put out the wrong voltage (which might damage your iThing).

Again, not trying to discourage you, just keeping you abreast of the various possible things that might happen, in an effort to prevent some bad outcome to the experiment.

But... carry on!

Renton Maclachlan · July 10th, 2011, 06:55 PM

Well...I've run the ipod through a laptop and the interference was not evident at all...so this suggests we're on the right track...

Jim Andrada · July 10th, 2011, 07:44 PM

Dumb question - could you ALWAYS run it through the laptop? Or plugged into a PC that's always on? Using a PC as a power supply may sound strange, but if it works...

Chris Harding · July 10th, 2011, 08:21 PM

Hi Guys

Renton is also communicating via another forum and the RF disappears if the Ipod is power via the USB from a laptop (running off mains supply) So the problem definately comes from the PSU he is using!!!

More than likely a decent switched PSU will solve all the issues and, as already mentioned, it is critical that it's voltage regulated!! I very much doubt whether the Ipod would like the standard "Christmas Tree Lights" style of adapter even if it states "5 volts" ...I'm pretty sure the Ipod would disappear in a puff of smoke very quickly!!!

Chris

Renton Maclachlan · July 10th, 2011, 10:29 PM

Jim..

I'm now looking at running it through a laptop full time. Thus I am in search of a real cheap one on an auction site here.

Chris

A super elcheapo laptop it seems to me now to be the easiest way to go...Nice and small and easy to put with the transmitter etc. Should be able to get a suitable one for a few $'s. With such a laptop it seems to me that I get what you're suggesting in a tidy package...

PS: and yes I confess to having put feelers out in a number of places, so as to get an answer as quick as I can. Thanks to all those who have responded...

Renton

Greg Miller · July 11th, 2011, 02:38 AM

Do I understand correctly that you're going to use a laptop instead of a $10 power supply?

Do you not consider this a "tidy package"??

I was going to buy a new couch for the living room, but on second thought I'll buy a car. Of course I'll need to cut a hole in the wall to get the car into the living room, but then I can just sit in the back seat of the car, and I won't have to shop for a proper couch. Yeah, that's the ticket...

Renton Maclachlan · July 11th, 2011, 03:11 AM

I hear what you say...but I'm hoping to get a laptop for $10... :-) ...which has the power supply and the usb port, and all I need to do is plug the things in an I'm under way...and I know it works! Don't even need to turn the computer on. Just switch the power to it on...

Greg Miller · July 11th, 2011, 08:28 AM

Ah... I find that interesting. It never occured to me that a laptop's USB ports would have any voltage available, unless the laptop is turned on. Perhaps you've stumbled onto an interesting scientific discovery... ;-)

Renton Maclachlan · July 11th, 2011, 01:32 PM

Actually I was wrong re the computer not needing to be 'on'. I tried it on a laptop last night and an ipod did not start charging until the computer was turned on. Bother...

Jay Massengill · July 12th, 2011, 07:39 AM

I believe it depends on the computer and the operating system. My recent notebook computer with Windows 7 brings up a power setting dialogue when something is plugged into a USB port. I haven't fully explored what the options are, but I think the USB ports can still put out power when the computer is in sleep mode at least.

Renton Maclachlan · July 12th, 2011, 01:35 PM

Thanks Jay, I'll check that out.

Doubt I'll get a win7 computer for $10 :-(

Greg Miller · July 12th, 2011, 08:44 PM

You could get a linear regulated "wal wart" for $10.00. But for some reason you seem to keep fighting the simplest and most obvious solution. 8-|

Renton Maclachlan · July 12th, 2011, 11:28 PM

Greg...not so.

I went to the local Dick Smith (NZ doesn't have Walmart) today to check out your suggestion and they don't have linear power supplies that put out 5v. 4.5v and 6v yes, but not 5v. I will pursue this because as you say it would be the simplest solution. They won't come with usb plugs (I'm told) so a modification will need to be done...

Greg Miller · July 13th, 2011, 07:45 AM

Once you make the analogy to WalMart, I see why you're having a hard time of it. I would never look for something like that at WalMart. If I asked them for a power supply, I'd have to walk over to the display and point at it, so they knew what I meant. They're good for cat food and toilet paper, but that's about as specialized as they get.

What happened to your "knowledgeable" local electronics store? (Or was that Dick Smith?) Can't they get you a linear regulated "wall wart"? Or can't any of the employees recommend a mail-order vendor that could supply one?

I would look for a dealer specializing in only electronics. Here we have numerous good mail order places: Jameco, Digi-Key, MCM, Parts Express, Newark, ad infinitum. That's the sort of place that will have what you want.

A quick look in a few of those catalogs convinced me that the sort of thing you want does exist. But the difficulty is, these are US dealers, and the linear regulated supplies they sell all have 125V, 60Hz mains input. (If I had seen one with 50Hz input, I would have pointed you at the link.) So I guess you need to find a NZ/AU/UK dealer who has them with 50Hz input at your local voltage.

Don't you know anyone who's an amateur radio operator? Or someone who teaches electronics at the local high school? People like that can probably recommend the right kind of vendor. Really, we have identified exactly what you need to solve your problem. But I know nothing about electronics vendors in NZ. Surely you have some resources locally who can name some vendors, or hand you a catalog, or somehow point you in the right direction.

I really do wish you luck!

July 10th, 2011, 05:10 PM	#16
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Thanks Greg, I don't know anything about electrics and electronics and so there is no way I could build something (even though I am more than a tinkerer and make stuff all the time!). I've just had a long talk to a helpful guy in a local electronics store exploring an idea suggested to me of using a computer psu (which I have) which he says will have the metal cage its in, earthed and so removing the RF. Just need to get a connector from the psu to usb to enable me to try this. Firstly however I will try powering the ipod through my laptop to see if I'm going in the right direction.

July 10th, 2011, 05:48 PM	#17
Greg Miller Trustee Join Date: Jan 2011 Location: Pennsylvania Posts: 1,786	Re: power supply interference with radio broadcast I certainly don't want to discourage your experiments there, and I encourage you to do on in some direction... don't give up because a solution is possible. I would just mention that as soon as the wires exit the computer supply's individual metal box, they can act as antennas. If the circuitry is generating any RF noise, it can sneak out on those wires, and radiate from there. This normally isn't too much of a problem, because all the wiring is normally enclosed within another big metal box... the case of the computer itself. But if you are going to have those wires hanging out, connected to a USB connector, you might need to put ferrite beads on some or all of those wires to reduce the RF radiation. Also, a computer supply generates several different voltages: +5, +12, -12 at the minimum. I have heard (though have not discovered on my own) that the supply needs some finite electrical load on each of those buses, or else it may not operate correctly. The last thing you want is for the supply to lose its regulation, "run wild," and put out the wrong voltage (which might damage your iThing). Again, not trying to discourage you, just keeping you abreast of the various possible things that might happen, in an effort to prevent some bad outcome to the experiment. But... carry on!

July 10th, 2011, 06:55 PM	#18
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Well...I've run the ipod through a laptop and the interference was not evident at all...so this suggests we're on the right track...

July 10th, 2011, 07:44 PM	#19
Jim Andrada Inner Circle Join Date: Feb 2007 Location: Tucson AZ Posts: 2,211	Re: power supply interference with radio broadcast Dumb question - could you ALWAYS run it through the laptop? Or plugged into a PC that's always on? Using a PC as a power supply may sound strange, but if it works...

July 10th, 2011, 08:21 PM	#20
Chris Harding Inner Circle Join Date: Jul 2009 Location: Perth, Western Australia Posts: 8,441	Re: power supply interference with radio broadcast Hi Guys Renton is also communicating via another forum and the RF disappears if the Ipod is power via the USB from a laptop (running off mains supply) So the problem definately comes from the PSU he is using!!! More than likely a decent switched PSU will solve all the issues and, as already mentioned, it is critical that it's voltage regulated!! I very much doubt whether the Ipod would like the standard "Christmas Tree Lights" style of adapter even if it states "5 volts" ...I'm pretty sure the Ipod would disappear in a puff of smoke very quickly!!! Chris

July 10th, 2011, 10:29 PM	#21
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Jim.. I'm now looking at running it through a laptop full time. Thus I am in search of a real cheap one on an auction site here. Chris A super elcheapo laptop it seems to me now to be the easiest way to go...Nice and small and easy to put with the transmitter etc. Should be able to get a suitable one for a few $'s. With such a laptop it seems to me that I get what you're suggesting in a tidy package... PS: and yes I confess to having put feelers out in a number of places, so as to get an answer as quick as I can. Thanks to all those who have responded... Renton

July 11th, 2011, 02:38 AM	#22
Greg Miller Trustee Join Date: Jan 2011 Location: Pennsylvania Posts: 1,786	Re: power supply interference with radio broadcast Do I understand correctly that you're going to use a laptop instead of a $10 power supply? Do you not consider this a "tidy package"?? I was going to buy a new couch for the living room, but on second thought I'll buy a car. Of course I'll need to cut a hole in the wall to get the car into the living room, but then I can just sit in the back seat of the car, and I won't have to shop for a proper couch. Yeah, that's the ticket... Attached Images

July 11th, 2011, 03:11 AM	#23
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast I hear what you say...but I'm hoping to get a laptop for $10... :-) ...which has the power supply and the usb port, and all I need to do is plug the things in an I'm under way...and I know it works! Don't even need to turn the computer on. Just switch the power to it on...

July 11th, 2011, 08:28 AM	#24
Greg Miller Trustee Join Date: Jan 2011 Location: Pennsylvania Posts: 1,786	Re: power supply interference with radio broadcast Ah... I find that interesting. It never occured to me that a laptop's USB ports would have any voltage available, unless the laptop is turned on. Perhaps you've stumbled onto an interesting scientific discovery... ;-)

July 11th, 2011, 01:32 PM	#25
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Actually I was wrong re the computer not needing to be 'on'. I tried it on a laptop last night and an ipod did not start charging until the computer was turned on. Bother...

July 12th, 2011, 07:39 AM	#26
Jay Massengill Trustee Join Date: Jul 2003 Location: Burlington Posts: 1,976	Re: power supply interference with radio broadcast I believe it depends on the computer and the operating system. My recent notebook computer with Windows 7 brings up a power setting dialogue when something is plugged into a USB port. I haven't fully explored what the options are, but I think the USB ports can still put out power when the computer is in sleep mode at least.

July 12th, 2011, 01:35 PM	#27
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Thanks Jay, I'll check that out. Doubt I'll get a win7 computer for $10 :-(

July 12th, 2011, 08:44 PM	#28
Greg Miller Trustee Join Date: Jan 2011 Location: Pennsylvania Posts: 1,786	Re: power supply interference with radio broadcast You could get a linear regulated "wal wart" for $10.00. But for some reason you seem to keep fighting the simplest and most obvious solution. 8-\|

July 12th, 2011, 11:28 PM	#29
Renton Maclachlan Trustee Join Date: Jul 2007 Location: New Zealand Posts: 1,180	Re: power supply interference with radio broadcast Greg...not so. I went to the local Dick Smith (NZ doesn't have Walmart) today to check out your suggestion and they don't have linear power supplies that put out 5v. 4.5v and 6v yes, but not 5v. I will pursue this because as you say it would be the simplest solution. They won't come with usb plugs (I'm told) so a modification will need to be done...

July 13th, 2011, 07:45 AM	#30
Greg Miller Trustee Join Date: Jan 2011 Location: Pennsylvania Posts: 1,786	Re: power supply interference with radio broadcast Once you make the analogy to WalMart, I see why you're having a hard time of it. I would never look for something like that at WalMart. If I asked them for a power supply, I'd have to walk over to the display and point at it, so they knew what I meant. They're good for cat food and toilet paper, but that's about as specialized as they get. What happened to your "knowledgeable" local electronics store? (Or was that Dick Smith?) Can't they get you a linear regulated "wall wart"? Or can't any of the employees recommend a mail-order vendor that could supply one? I would look for a dealer specializing in only electronics. Here we have numerous good mail order places: Jameco, Digi-Key, MCM, Parts Express, Newark, ad infinitum. That's the sort of place that will have what you want. A quick look in a few of those catalogs convinced me that the sort of thing you want does exist. But the difficulty is, these are US dealers, and the linear regulated supplies they sell all have 125V, 60Hz mains input. (If I had seen one with 50Hz input, I would have pointed you at the link.) So I guess you need to find a NZ/AU/UK dealer who has them with 50Hz input at your local voltage. Don't you know anyone who's an amateur radio operator? Or someone who teaches electronics at the local high school? People like that can probably recommend the right kind of vendor. Really, we have identified exactly what you need to solve your problem. But I know nothing about electronics vendors in NZ. Surely you have some resources locally who can name some vendors, or hand you a catalog, or somehow point you in the right direction. I really do wish you luck!