I have been watching some videos recently, and noticed a very weird car alarm in the background. Well, I realized at some point that it wasn't an alarm, it was actually the traction sound of the train. This seems be a noise across all Siemens trains, older and newer. You can hear it here for example. Has anyone else noticed this? Any idea where it comes from? I only heard it from Siemens trains so far, both AC and DC units, but nowhere else
The Flying Saucer noise? In the early 1990s British Rail put some quite onerous restrictions on the amount of interference that VVVF AC motored trains can put out on the UK network, especially on the DC network which didn't have AC Filtering because up to that point the DC motored stock didn't generate interference. I remember Eurostar sets changing signals as the fields they were generating were inducing currents in signal cabling. There were a few solutions, either notch out the problem frequencies, like 323s with their many many jumps as the Inverters avoid problematic harmonics - I think Siemens chose to oscillate to avoid causing issues at any particular frequency. As their first order was a DC design they carried the mitigation over to the AC versions. At least up until the 700/707 which have their Inverters run different profiles depending on whether they are on AC or DC. Also long term there has been a lot of work on the NR side to upgrade the signalling to be immune to AC Traction's interference. The GWML was redone prior to electrification, but the ECML had major issues with the 800s blasting it with high power interference.
Just like the class 700, unmistakable sound, I always know I've missed the train when I hear this as I run down the stairs!
