I was driving an ICE service from Frankfurt to Fulda and I was chasing another ICE all the way in. Naturally I was encountering red signals. Some of them did not have active 500 Hz magnets preceding them. This was maybe 30 km south of Fulda, before the tunnel. Is it normal for some red signals to not be protected with 500 Hz magnets?
Block signals are generally not protected by a 500hz magnet, so that's probably what you encountered.
If the thing that the signal is protecting is sufficiently far away from it, you don't need a 500 Hz magnet. If you're only protecting the train in front (instead of any junctions or whatever), it's considered sufficiently unlikely for one train to stop immediately after passing a signal and the following train to SPAD at the same time. (note that I'm not calling them block signals - in German nomenclature, a block signal can very much protect a junction and therefore require a 500 Hz magnet)
mkraehe#6051 that makes perfect sense! I was kinda heading in that direction logically. The signals at that point are pretty far apart, and the trains are really moving so it stands to reason that a rear end collision is extremely unlikely. Plus, should the driver fail to react to the yellow signal, the 1000Hz protection would intervene anyway.