How can a signal (e.g. an analog radio signal) be 'stretched' in time, so that the frequency is halved and the signal takes twice as much time? It's straightforward to do in a computer, but can it be done with analog components?
(This is different from what a heterodyne radio receiver does: it shifts a signal from a high to a lower frequency, but the signal still takes up the same amount of time.)
Recording and reading back at a slower speed would be one way to do this, but that would require slow mechanical components and not be able to deal with faster signals.
Background: I'm not building anything for which I need this, but I'm wondering if something like time division multiplexing could work in the pre-digital age or what it would take to create it. That is also why a method like recording to tape and slowed down playback would not work. If the multiplexed pieces of signal are short, the mechanical systems of a tape would not be able to keep up.
Edit The relation with time division multiplexing: I was thinking that tdm could be implemented with such a technique. Take two continuous signals, split them up into (say) microsecond intervals, squeeze each microsecond into half a microsecond (increasing the frequency), then interleave the squeezed segments of signal from both streams. To demodulate, reverse the process by stretching the odd or even intervals.