bobvan13

Thanks for noticing this post. It covers many of the questions that arose in the comments on my Part I post. It also details two more shortwave trading sites around Chicago.

Good point, a one-time pad is not needed.

Either way, the likelihood of loss between TX and RX means that you can't advance the cipher as bits arrive. I'm thinking you'd have to advance based on GPS-sync'd clocks. Given that each bit is at least 10's of microseconds, GPS sync is plenty good.

Listening is the easy part. But the sender would be foolish not to strongly encrypt what they send. Are you really "listening" if all you get after decoding is pseudo-random bits?

A one-time pad is the right idea. I would send it on fiber at night before the markets open and then use bits from it as the market trades. A few MB per day would be plenty, given the dialup-like speeds of shortwave. That would go through a 10 gbps fiber in milliseconds.

The actual encryption of each bit just require an XOR on each end of the link. That's about half a nanosecond on a Xeon or one clock cycle on your FPGA.

A jammer wants to be close to the receiving antenna so he can use less power. Yet he wants to be far away so he's less likely to be caught. Willfully interfering with any any radio service is illegal in any regulatory domain AFAIK.

There is some latency savings because the radio path is far straighter than the fiber path, even considering the ricochetting off the ionosphere and the earth. But the bulk of the latency savings comes from the fact that radio waves move at the full speed of light while photons through fiber only move at about 2/3 of that speed. So yeah, it works out to about a 10 ms savings on shortwave compared to fiber.

The license applications list a range of frequencies where operation is allowed. Indeed, many SWLers have documented such transmissions, e.g. https://www.youtube.com/watch?v=ySzpz8LWrjA The trouble is that when you do listen, you either hear test signals as recorded on YouTube, or you just get pseudorandom noise because it's encrypted.

Yup, it stands alone well. I give it a strong recommendation for accuracy and storytelling.

Right. A shortwave link would be used in addition to a fiber link, not as a replacement for it. Assuming ACKs aren't latency sensitive, they could flow back over the fiber.

Yes, it has to bounce, but the number of times it bounces is dictated by the takeoff angle, as is the path length of each bounce relative to ground traversed. You aim for takeoff angles around 12 degrees. Since cos(12 degrees) ~= 0.98, there's not much path length added by the bouncing. So you still end up WAY ahead of fiber. I'll detail a stacked-curtain, log-periodic antenna used at another Chicago-area site in a forthcoming post.

Yes, well said. I think you're making an important distinction. Shortwave is old technology, but combined with SDR, this is a novel application of it AFAIK.