Does a lower frequency signal travel the same speed? 1hz? I suppose it would be the same because the tether would have immense mass over it's length. So even though I'm picturing an impractically long tether moving as one solid length to tap slow morse code, the mass would be unfathomably high and therefore inducing significant stretch. That's without getting into vibration kinetic energy being lost to heat along the way

I'm obviously not genuinely proposing this. It's just a brain exercise.