Interference on AM.

[lightning]

Can make it impossible to listen to AM
l had my 1937 Marconi on Radio 5 today
and suddenly the station faded in a hash of noise and static.

Oh no the old girl has broken down already l thought, but no, it was my missus turning on the bathroom light (5 LED down lighters)

l was wondering. Does this interference come via the mains, or over the air? l was only thinking that if it was mains borne then a mains suppression extension lead might cure it?

Otherwise, it's no bathroom lights while the radio is on! These lights are two rooms away, which is why l wondered if it was coming via the mains.

There's a lamp on top of the radio with a fluorescent energy saving lamp in it, and that doesn't cause any interference at all.

[Andrew2]

Some LED lights are very noisy, as they use internal switch-mode drivers which are not fitted with suppression/filter components. So all the switching noise is pumped out into the mains wiring which acts as a nice big antenna, radiating the noise all over your home.
In other words, although the noise is generated by the devices themselves, it is arriving at your radio by the 'normal' means, via the airwaves just like any radio station.
Did you fit these yourself? Are they wired directly to the light switch or is there a 'transformer' hidden in the ceiling?

[lightning]

They were fitted by the builders, they are mains GU10 style lamps so the PSU must be the size of a sugar cube.

Fortunately the other LED lamps in the house don't seem to radiate so much interference. But AM is generally pretty bad for loud buzzing and other interference. lt's much better at night when all the lights are off and l occasionally sit up in bed with a pocket radio listening to various AM stations.

[emeritus]

When we stayed at Warners the year before last our bedside lamps used Chinese-manufactured Osram LED bulbs. No interference detectable on my transistor radio on AM until it was within about 2" of the bulb, and even then it was only low level background noise.

[agardiner]

I receive a number of AM stations at home, all nice and clear except for Smooth. This is the strongest signal yet has a fairly heavy hum on it. Sounds like 50Hz and I have not been able to track down the interference source at all.

I have to avoid Smooth when first powering up a repaired set, otherwise I think the main cap is about to pop!

[Graham G3ZVT]

I was plagued with that, but I eventually found the cause; in this case it was the landing light. The 2-way switch wiring seems to form a loop aerial.
The problem was there even if the light was off, but a different make of bulb helped.

[winston_1]

Originally Posted by lightning

They were fitted by the builders, they are mains GU10 style lamps so the PSU must be the size of a sugar cube.

Call the builders back and tell them they have fitted products that don't comply with the wireless telegraphy acts or whatever and ask them to replace them at their expense.

[PaulR]

I have found that a class x capacitor across live and neutral inside a plug is useful for reducing modulation hum. It can be moved around the house to get the best effect.

At one point my pantry transmitter became almost unusable because of modulation hum and a class x cap in a plug helped greatly. Whatever was causing it eventually stopped as now I can use the transmitter without using the plugs. They don't work for LW interference, though.

[lightning]

Sorry for my lack of knowledge, but what's a class X capacitor?

[PaulR]

Class X capacitors are constructed so as to make them safe to be connected across the mains. There is a lot about them on the internet. They are available from the likes of Ebay. I have found that there is just enough room inside a 13A plug to fit one connected between live and neutral. It may or may not help but thay are fairly cheap and would be worth trying.

In view of the amount of mains borne interference about I am starting to fit them in radios I restore now. This was common in the past but the capacitors used tend to break down after so many years and the usual advice is to cut them out. I certainly wouldn't keep an original one in place but I think that replacing them is a good idea.

**If you do this be aware that the capacitor in the plug will remain charged when you unplug it and could give you a nip if you touch the pins. Not a good idea if there are children about or someone who doesn't understand this.**

[Ian - G4JQT]

Google is your friend!

https://www.allaboutcircuits.com/tec...-y-capacitors/

[Craig Sawyers]

If the rubbish is getting through the mains, rather than over the air, the other solution is a large common mode choke and filter https://gm3sek.com/2019/10/11/clean-up-your-shack-2019/

Craig