🚀 go-pugleaf

Mercury delay lines, as used in EDSAC and UNIVAC I, I believe used
quartz transducers and pulses of RF propagating in the mercury.
Hence the binary data modulates (on/off) a radio-frequency signal.
It's detected at the receiving end and reconstituted into data, and
also re-introduced at the sending end so that the stream of bits
in the mercury recirculates forever.

Mercury delay lines were also used in radar and in distance
measuring equipment for air navigation.

Later there was a technology using solid wire as the delay medium,
with the data being represented as a torsional pulse in the wire.
This didn't use the RF carrier; the data bits went directly into
the wire.  I've seen this technology used in transistor computers:
Packard-Bell 250 and Royal Precision RPC something or other, I forget
the model number.  The transducers were magnetostrictive.

There were also some very high speed delay lines that used something
like a glass prism as the delay medium. Signal was introduced at one
face, traveled through the material to another face, where it was
reflected at an angle to another face, and so on through several more
reflections until it emerged from the output face.