[PRCo] Re: MetroRail Signalling

[Joshua Dunfield]

2009/6/29 Schneider Fred <fwschneider at comcast.net>:
> Russ Jackson called me this evening ... I finally had an opportunity
> to ask him to explain the Washington Metro signal / ATO / ATC system.
>
> His answer is simple.   It is fundamentally no different from the old
> Pennsylvania Railroad signals that I understood except that it uses a
> signal frequency in the audible range ... if amplified you would be
> able to hear it ... the frequency is in the 1000s of cycles per
> second instead of in the 100s of cycles per second.

I'm out of my depth here, but frequencies in the 100s of Hz are well
within audible range; a tuning fork produces 440 Hz, and the lowest
note on a piano is about 25 Hz, IIRC.  So that part of the explanation
doesn't seem quite right.

Digressingly,
-j.