The AM Radio test

Reading around the posts I’ve seen this mentioned but what am I looking for? Away from my HiFi in an adjacent room I have my desk with an iMac on it, a NUC for Roon, a tp link router, and telephone underneath the desk there is a Draytek modem and a cornucopia of associated wall warts plugged into a random power strip. Given this is not in my listening room, does it matter? If it does what do I look for and what can I do to improve? Cheers.

The radio test is a convenient way to detect RFI from the ever increasing number of electrical appliances we use in our homes. Just turn on the radio, tune it so that no station is audible, and point the aerial at any electrical devices. Wall wart power supplies, phone chargers, LED and fluorescent light fittings are all potential culprits.

Many chargers have a ferrite clamp on the DC output lead, which is there to cut RFI that may be travelling down the cables, and manufacturers put them there to help devices meet RFI emission regulations.

The fact that a device emits RFI does not necessarily mean that it will find its way to your HiFi or other places where it might cause problems. If you find a noisy device, try tracing the noise along any cables connected to it. Chances are that most of the noise will die off as you move the aeriel away from the body of the device, indicating that it’s not really causing problems elsewhere. Nevertheless I tend to think of it as good housekeeping to minimise the problems at source rather than using isolating gadgets to reduce it. For example, many modern light fittings are very noisy, and I have managed to identify bulbs that are quiet and use them wherever I can.
Networking equipment can also be culprits, so I keep routers, servers, switches etc away from the HiFi where possible.


Yes. LED lighting is worth checking out.

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So I tried this earlier and the static noise goes much much higher when I go near the nest of cables and wall warts under the desk, also when I go near the iMac and the router, actually more like an old motorbike near the router! However it goes back to normal near the HiFi so I guess nothing to concern myself about.

It’s easy to get paranoid about this stuff, but if your HiFi and the cables behind the rack are silent it’s probably not worth worrying about.

As a test you could try turning off the offending devices and see if the sound changes. Chances are it won’t, or maybe it gets worse and you can take steps to mitigate it - or maybe the RFI will make your system sound subjectively better.



Can you give any examples of quiet bulbs? I find lots of my LED bulbs (or perhaps the mains unit) interfere with FM, DAB and/or Freeview.

The only completely silent LED bulbs I found were some of the filament type designed to replace traditional bulbs. Even then, not all the brands I tried were silent, but the Sylvania ones were. Readily available online, the last I bought were from Toolstation, £10 for a box of 4.

Thanks for that - I shall try some Sylvania bulbs - the ones I have are not the bayonet cap type (MR11? something like that) but maybe they do better with their equivalent.

They do screw fittings too, and a few different shapes and sizes.

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