That's an interesting one. Maybe complicating instructions might take too long to encode, but making it a simple buy/sell trigger for one particular security could work? But also going over too long a distance means the stock markets are closed in that part of the world.

There is also a satellite company LeoSat that was trying to build a low latency long distance network of low flying satellites with laser links between them. Guessing that's a "tad" :-) (few billion) more expensive than a pair of shortwave transceivers. But if money is not an issue they say they can do 1.5x faster than terrestrial speed:

http://leosat.com/media/1115/leosat-finance.pdf

100ms NY to Tokyo, for example. Not bad.

> Why aren't HFT firms using short wave radio (DXing)?

They are. See mshook's response, with nice reference links downthread: https://news.ycombinator.com/item?id=16196339

Those are microwave which basically need line of sight? I was thinking of lower frequencies which can sometimes go hundreds of kilometers without repeaters.

Bandiwdth, mostly.

The lower you go in frequency, the less bandwidth is available.

The entire "HF" spectrum is ~30 MHz. My Wi-Fi at home uses a wider channel than that.

The lower frequencies -- that will travel across the ocean, unaided -- don't have anywhere near the bandwidth necessary (to support the throughput that they need).

You want your severs as close as possible to an exchange. Even 2 miles is a noticeable increase in latency.

One reason may be that the FCC is touchy about encryption.

The throughput probably isn't high enough.

Maybe the throughput could be increased using a bunch of MIMO antennas?

No, the throughput available at these frequencies is measured in bits per second.

PSK31 is 31 bps, but that's with ~100 Hz between channels. DXing is common in the 14 MHz band, so you could probably get to the megabits-per-second range before Physics (or the FCC) stops you.