I used to work in high-frequency trading. I had several tabs permanently open to the live weather radar feed for regions where we had microwave towers: the NE USA, the South of England, the Alps...
I used to be in an adjacent field and we used to joke about when the HFT guys were gonna get working on some neutrino detectors & sources to signal straight through the Earth. You could use them for science on the weekends!
Sounds awesome, to be able to send a signal directly through the whole earth from point to point. It also sounds like origin story of X-Men or a new cancer
I'm curious to know where your towers were. Do you know if they still exist? Were your microwave antennae co-located on other operators' towers (e.g. those for VHF radio), or did your company have towers all to itself?
Without going into anything confidential - we had some of our own hardware, but generally rented capacity from firms like [0]. Some towers were custom built for HFT, some were shared with other types of users.
A famous blog post investigating some of the towers as an outsider, at [1], will be of interest to you.
If you want to guess where they are, get a globe, find the datacentres where electronic exchanges operate (it's not a secret: Chicago, New Jersey, London, Tokyo, Frankfurt, Zurich...) and draw the straightest possible lines between pairs of them. Microwaves don't cross the ocean.
Traditional optical fiber has glass in the middle. The speed of light in glass is only about 66% of the speed in air, so microwave is always faster if you can get a reasonably straight path for both.
There now exists hollow-core fiber, where the light travels down an air gap in the middle, which is theoretically competitive with microwaves/lasers/etc. How much this is being used is a secret, but microwave transmission definitely hasn't gone away.
