power supply interference with radio broadcast
 

This thread is 'All things audio' meaning audio with video...but I thought someone here may be able to help with a radio issue I have...

I've been running a couple of low powered radio stations for about ten years here in NZ. I use a pre-recorded program. It has gone well...only I have a hiccup...

Until recently I used to run my program from a DVD in a DVD player but wanted to go solid state to avoid mechanical breadkdowns, so have been running for a while from a 16gb Ipod.

However when the ipod driving one of my stations is running on a usb power adapter plugged into mains supply, it causes a lot of interference on some short wave bands within the house I'm transmitting from. I haven't heard it has caused any issue for neighbours.

Pull the usb power supply to the ipod and the interference goes away. Plug it back it and there it is.

I need to do something quick as the ipod won't run for ever on batteries!

Does anyone have any ideas as to how I could power the ipod without getting the interference?

Re: power supply interference with radio broadcast
 

How long does it need to run for? One of these fully charged, plugged in to an iPod will keep it going for quite a while.

I bought one for my iPhone 3 because the battery life was dismal, and bought a second when I thought I'd lost it. The price has come down geatly, and the kit includes its own charger which might be cleaner on the RF interference front than the one you are using.

Or you could just try the Heath Robinson trick of covering the iPod, its charger and as much of the connecting leads as possible with aluminium foil and grounding it :-)

Re: power supply interference with radio broadcast
 

I often do theatre shows and have found that Mac laptop computers almost always give problems when running on mains, where as a windows based one doesn't... why I don't know.

My suggestions might start with the aluminum foil around the power supply, or use an isolation transformer on the audio connection... or try 240v - 240v (or 110 - 110v if applicable) isolation transformer on the mains side.
Is the mains power on the same circuit for both player unit and transmitter? If not this might minimise problems.

Re: power supply interference with radio broadcast
 

It needs to run 24 / 7 / 52...unattended...

Re: power supply interference with radio broadcast
 

Both transmitter and ipod are on the same circuit...

I have a UPS. Would that help? I haven't tried it yet.

Re: power supply interference with radio broadcast
 

Have you tried different mains-to-USB-power-adapters? There are lots and lots of them on the market, as well as USB-to-iPod cables from various manufacturers.

I'm not sure it would help, but a stereo isolation transformer like an Ebtech Hum Eliminator between the iPod and your audio system could be a good idea.

Re: power supply interference with radio broadcast
 

Not enough details/examples to narrow down the possible cause. It sounds like it might be related to the switch-mode power supply (SMPS) which operates at near-RF frequencies. Alas, the old-technology linear power supplies (with a heavy iron transformer operating at mains frequency, 50Hz) are all being replaced by more modern (and inexpensive) SMPS.

You could find an old-fashioned linear 5V wall-wart (they tend to be significantly heavier and larger) and wire it into the proper cable for your iPod.

Or you could try some ferrite devices that are used to filter out this kind of noise. You see some USB cables that have big lumps around one or both ends of the cable. And electronics vendors sell ferrite in various shapes that you can clip around a cable or thread a cable through. I have seen some extreme cases where a large doughnut-shape ferrite torroid had the offending cable looped through several times to fully attenuate the offending noise.

ferrite core - Google Search

Re: power supply interference with radio broadcast
 

I was going to say exactly the same thing Richard said.

Plug in the power adapter, without the iPhud connected to it, and see if the adapter itself is the source... I would bet it is. Then, yes, find an old linear regulated adapter and that should cause no problems.

Re: power supply interference with radio broadcast
 

Thanks all...

I've now tried magnets on the cable and wrapping the Usb power supply in many layers of aluminium foil but there was no change.

With the Ipod running on batteries - unconnected to the power supply but with the power supply plugged in and the power on, there is no interference. As soon as the ipod is connected to the power supply the interference starts...

I am going to try a computer PS directly powering a usb plug and see if that makes a difference.

Re: power supply interference with radio broadcast
 

Aluminum foil is a joke for this kind of problem.
Nobody suggested "magnets" because that won't work either.
Since you have not tried ferrite inductors, we don't know if that is the solution or not.

Re: power supply interference with radio broadcast
 

'Aluminum foil is a joke for this kind of problem.
Nobody suggested "magnets" because that won't work either.
Since you have not tried ferrite inductors, we don't know if that is the solution or not. '

Opp's...not magnets - ferrite inductors from a reputable electronics store...
Re Aluminium foil...I'm just trying what some have suggested. It certainly didn't do anything...and neither did the ferrite inductors...

Re: power supply interference with radio broadcast
 

Yes, I suggested that but the :-) at the end is the giveaway - it was a joke, but not entirely irrelevant. The earthed/grounded foil would form a "Faraday cage" - but only if it enclosed the entire system, which it wouldn't because of the mains and audio wiring sticking out. The theory of the Faraday Cage does work when correctly designed as the foil screening fitted inside many electronic iappliances will testify.

Sorry if I have misled anyone in this discussion. Surely it can't be that hard to find an RF clean power supply?

Re: power supply interference with radio broadcast
 

You say you're going to try a computer power supply, wired to a USB connector.

Be aware that almost all computer power supplies (with the exception of a few 286-era supplies that I can recall) are switching supplies. They, too, will most likely generate RF interference to some degree. True, they may be a bit cleaner than the no-name "wall wart" that caused your original problem, but they won't be 100% clean.

If you are really interested in an RF-free solution, you really need to get a supply with a linear regulator inside, nothing with high-frequency switched mode regulation (as was suggested earlier).

Re: power supply interference with radio broadcast
 

'If you are really interested in an RF-free solution, you really need to get a supply with a linear regulator inside, nothing with high-frequency switched mode regulation (as was suggested earlier).'

Thanks Greg. I certainly want to beat this. Do you have any suggestions as to a power supply that you think may be suitable?

Re: power supply interference with radio broadcast
 

Hi Renton,

As an amateur radio operator, and a sometimes FM-broadcast DXer, I am certainly aware of RF noise issues. Even the dreaded "CFL" or Compact Fluorescent Lamp puts out a lot of RF noise! The world is getting noisier and noisier.

I'm sorry to tell you that I can't suggest a specific make or model supply, especially one that is easily available to you.

But here's the deal. When we say a "linear regulator" what we mean is this. You start with a mains step-down transformer running at your mains frequency (50 or 60 Hz as may be), and step down the voltage to something in the right ballpark... perhaps around 6 or 7 volts. You rectify the output, and filter that... the result will be around 9 or 10 volts DC. Then you run that through an inefficient old-time regulator with a zener diode and some transistors to get your desired 5 volts. Wasteful of power... runs rather warm.

The newer "switching" supplies directly rectify the mains voltage and filter it (here in the US, 125VAC gives you roughly 175VDC). Then you switch that high-voltage DC on and off at a very high frequency. The resulting square wave goes through the step-down transformer and is rectified and filtered again to produce the desired 5 volts. More efficient... usually runs cooler. Higher frequency means you need less iron in the transformer, and less capacitance in the filter caps. That means smaller size and lower price... that's why switchers are popular.

The RF noise problem is caused by the high frequency square waves which can put out harmonics all over the RF spectrum. Very hard to control unless the entire circuit is inside a grounded metal case, the wiring goes through a ferrite choke immediately upon leaving said case, etc. etc.

Switched mode supplies need much less iron in the transformer. So when shopping for a new "wall wart," heft it in your hand. If it feels as light as your old, noisy one, it is probably another "switcher." If it's bigger and heavier, that probably means the transformer has a lot more iron (to operate at mains frequency) so it is not a switcher.

Another thing... switched mode supplies typically will accept a very wide range of input mains voltages, perhaps even 100 - 240 VAC. Linear regulators will probably be a narrower range, perhaps 110 - 125 VAC or something similar. Switched mode supplies most likely accept 50-60 Hz mains input. Some linear supplies are also dual-frequency, but some are single-frequency. If you find a supply that is narrow voltage range and only one frequency, it's almost surely a linear regulator.

If you're buying from a really legitimate, and somewhat commercial vendor, their product description might even specifically tell you whether or not it's a switcher. If you're buying from the neighborhood battery shop or music store, they may not know what they're selling.

I also note that switchers are becoming more and more common; older linear regulated supplies are becoming "old hat."

AND REMEMBER: There are also unregulated supplies out there. Those will probably blow up your iThing. So be 100% certain the supply you buy is regulated!

Of course you could build one yourself, if you're a tinkerer. ;)

Good luck, and let me know how you make out.

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.

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!

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...

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...

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

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

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...

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...

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... ;-)

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...

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.

Re: power supply interference with radio broadcast
 

Thanks Jay, I'll check that out.

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

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-|

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...

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!

Re: power supply interference with radio broadcast
 

Apologies Greg, I read 'wal wart' as 'wal mart'. I assumed Walmart may have had an electronics dept that supplied these sort of things.

At present I am trying all sorts of avenues. I now know more specifically what to ask for and will ring another shop today...

Thanks for your help...:-)

Re: power supply interference with radio broadcast
 

Renton:

Dang, I'm sorry for the confusion. I didn't notice the typo until you mentioned it just now. "Wall wart" is our nickname for those fat little power supplies that plug into a wall outlet.

I share your frustration and I really wish I knew the name of some appropriate vendors in NZ. I don't even know anyone who's ever been in NZ, so I have no idea where to start from here.

And believe me, if I could find one online with a 50Hz input, I would send you the link.

Actually, while we're on that train of thought, what is your line voltage there? Wikipedia says 230V, 50Hz, but they're not always correct.

Re: power supply interference with radio broadcast
 

'Don't even know anyone who's ever been in NZ.' Man you've never lived! Pocket wonder world. Successive guments have been progressively wreaking the place (as seems to be happening just about everywhere in the West), but the land is something else...

Yep we're 230v...never thought about Hz.

Probably the best supplier around here is jaycar.co.nz followed by Dick Smith dse.co.nz

Re: power supply interference with radio broadcast
 

I'll second the comments about NZ - it's really lovely. When I worked out of Tokyo flogging IBM's storage products in Asia/Pacific I had at least one trip a month to NZ and absolutely loved it. I even took my nephew there for his 11th birthday. Did the farm stay thing near Christchurch for a week.Happiest sheep I've ever seen (particularly compared to the poor sheep who have to eke out an existence in the deserts of Oz)

Re: power supply interference with radio broadcast
 

Jim.

Unfortunately Christchurch has been shattered by a number of servere earthquakes over the past year and it is not the delightful city it was...people have left in droves, and sections of the CDB are in ruins...something like 5000 houses are to be demolished...many of the beautiful stone churches, including the iconic Cathedral have effectively been destroyed...every new big shake has liquifaction flooding some suburbs...cry...

Re: power supply interference with radio broadcast
 

Yes, I know what a mess it is. It must still be heartbreaking even after all this time.

These things quickly fade from the international news, but are still very real for all those affected.

I lived in Japan for quite a few years and my wife is Japanese and we watch NHK every day. From what we see here in the US, the earthquake/tsunami is "old news" but it still takes up about 20% of NHK airtime. Fortunately her family is from Southern Japan, but, just as I've spent time in Christchurch, my wife and I frequently vacationed in some of the towns that were demolished and many of those ghastly scenes were from places we knew.

Maybe the moral of the story is that wherever I go, bad luck follows!

Re: power supply interference with radio broadcast
 

Renton,

Thanks for providing those names.

I just scanned Jaycar's online catalog. There are numerous 5V power supplies, but, by damn, they all seem to be switchmode! So I fired off an EMail to their customer service department, asking if they have any linear supplies hidden away.

If that draws a blank, I'll try Dick Smith next time.

Re: power supply interference with radio broadcast
 

Hi Renton..................

Didn't really understand your reference to a "USB Power Supply" plugged into you Ipod, so didn't really get too excited.

However, as this is rumbling on, may I suggest something?

Still not entirely sure of the "what is plugged into what" chain with this, but here goes:

Dive into Jaycar (they're cheaper than DSE usually) and buy a couple of ferrite torroids that are appropriately sized for the cable(s) being used, such that you can pass the appropriate power cable (s) through the torroid at least 4 - 5 times, wound tightly to the torroid ring.

That should kill any HF noise passing down the power cable, though it can be a pretty moveable feast.

I've tried running a battery fed CB system off a linear power supply of my own build (a damn good one too) and even that couldn't keep the bloody stuff out of the transmitter.

A few more details about cables and connectivity may give me a better insight into the problem.


CS

Re: power supply interference with radio broadcast
 

Thanks Chris

I got a couple of ferrite rings from Jaycar last saturday. I wound the cable through them as many times as I could get the usb plug through the hole and...there was not the slightest scrap of difference. So...they don't seem to work...

Soo...it's seems to be either a linear supply or an elcheapo laptop serving as a power supply...

Renton

Re: power supply interference with radio broadcast
 

Uhhhhh .. or you could ditch the iPod completely and use a real, purpose-built audio recorder ..... Seems like you're going to a lot of trouble and expense to use what would ultimately be a marginal solution even if everything worked perfectly.