[Question] Metal Sign on Railroad Says "790Hz" (thelemmy.club)

submitted 3 weeks ago by rudyharrelson@lemmy.radio to c/amateur_radio@lemmy.radio

9 comments fedilink hide all child comments

Dunno if this is actually radio related, but thought this community might know something about it.

I was walking down a stretch of railroad that I haven't explored before when I happened across this metal sign nailed down to the tracks.

It's pointing toward the nearest railroad crossing and says "790Hz". Is this a radio frequency one could listen on and hear when the train is passing by? Or something else? I don't know anything about trains

top 9 comments

sorted by: hot top new old

[-] sketchyenchantment@sh.itjust.works 13 points 3 weeks ago

You should check out this patent. When the train goes over a special section of track, it will trigger the signal at the nearby crossing

[-] in_my_honest_opinion@piefed.social 9 points 3 weeks ago

790hz is the switching signal, as the contacts corrode the resistance increases so they have to be tested on a schedule.

[-] rudyharrelson@lemmy.radio 3 points 3 weeks ago

Ahh, that makes sense. Thanks for the assist!

[-] vk6flab@lemmy.radio 3 points 2 weeks ago

The technology that's possibly in use on the railway is:

https://assets.new.siemens.com/siemens/assets/api/uuid:c9dbe06e-5daf-426d-97e8-c1a03562da91/sie-bro-pso4000.pdf

[-] TropicalDingdong@lemmy.world 2 points 3 weeks ago

Did you tune in?

[-] Evil_Shrubbery 2 points 2 weeks ago* (last edited 2 weeks ago)

Maybe a wiki/Balise?

But that looks passive & without electronics, just a plate bolted down?
Maybe it is just a simple sign about the signaling frequency (of some nearby wires) to the nearby crossing or station?

[-] The_Walkening@hexbear.net 1 points 3 weeks ago

If it's not something about signaling, it might be a resonance frequency - I could imagine sympathetic vibrations becoming problematic for the trackbed in spots due to the composition of the ground in some way, similar to earthquakes being able to liquefy soil.

[-] Multiplexer@discuss.tchncs.de 1 points 3 weeks ago

Definitely not an RF frequency, much, much too low.
Might be some wire based signalling for a railway switch or semaphore or so.
Perhaps ask in a train community?

[-] vk6flab@lemmy.radio 2 points 2 weeks ago

RF happens at plenty of lower frequencies:

https://en.wikipedia.org/wiki/Extremely_low_frequency

this post was submitted on 11 Apr 2026

28 points (100.0% liked)

Amateur Radio

2619 readers

7 users here now

General amateur radio (ham radio) chat, questions, and news

founded 2 years ago

MODERATORS

w0odl@lemmy.radio