Cardiff Central - possible interference from OLE on PA?

[anamyd]

Standing on platform 3 of Cardiff Central just now I noticed that when manual announcements were being made, there was a high-pitched buzz from the speakers that I recognised as being a noise related to the OLE, as I've also heard it from some EMUs. I'm just wondering how normal this is, or if it's some oversight or grounding issue since the electrification or something?

(Overhead Line Equipment)
(Public Address [System])
(Electric Multiple Units)

 

[Birmingham]

Could be anything surely. I’ve heard noise in PA announcements at stations which have no OLE for miles.

 

[anamyd]

Thing is though, it sounded exactly the sound I've heard coming from EMUs. Like, it was exactly that. Specifically that high-pitched buzzing/ringing. I wouldn't have posted or thought it was interference from the OLE if it had just been a 50Hz(/harmonics) ground buzz.

 

[Llanigraham]

LED light units can cause the exact same interference.

 

[dosxuk]

Thing is though, it sounded exactly the sound I've heard coming from EMUs. Like, it was exactly that. Specifically that high-pitched buzzing/ringing. I wouldn't have posted or thought it was interference from the OLE if it had just been a 50Hz(/harmonics) ground buzz.

The OLE runs at 50Hz too though, so if it was inducing a buzz into the PA it would be 50Hz. Higher pitched buzzes can come from all sorts of nearby equipment - basically anything with a power supply or doing some sort of power switching will cause harmonics that can become audible. Fluorescent lights used to be particularly bad for this, but they pale in comparison to some of the switched mode power supplies. On a modern EMU, the motor drive electronics will be a substantial cause of electrical noise - not the presence of the OLE.

 

[satisnek]

If it's only on manual announcements then that suggests interference getting into the microphone preamplifier, possibly something that has been installed alongside it?

 

[Dai Corner]

Did it get worse when an electric train was taking power? If not it probably wasn't the 25kV.

I concur that it's probably some cheap and nasty piece of equipment like a phone charger near the microphone.