Patterns in radio

One feature I find important about patterns is that often their limitations break the illusion of abstraction, and the underlying “reality” leaks through and you learn something new - this is a tiny example of that I’ve been meaning to document somewhere.

We use tiny radio transmitter/receivers for our woven maypole dancing robots which requires that every robot has a unique id number. These numbers are put at the beginning of every message broadcast as an address so the robot knows when it is being sent a message. However it is not recommended to simply use numbers like 1,2,3 etc for these addresses, from the documentation:

Addresses where the level shifts only one time (that is, 000FFFFFFF) can often be detected in
noise and can give a false detection, which may give a raised Packet Error Rate.

What they are suggesting is that in order get the best out of the system (i.e. most messages get through) you need to use numbers where the binary signal when transmitted over the air can’t be confused with background noise, so they need to be a little bit more complicated than that example 000FFFFFFF (in hexadecimal), which in binary looks like “0000 0000 0000 1111 1111 1111 1111 1111 1111 1111”.

The underlying analogue radio signal uses something called “Gaussian Frequency Shift Keying” which basically means it has one pitch for 0 and another for 1 and does a little pitch bend between them to reduce interference, so with 000FFFFFFF you’d just get one pitch then a slide to another.

Most of their examples use large numbers from repeated sequences with lots of alternating patterns with lots of A’s in them (in binary: 1010) - e.g. A7A7A7A708 - which looks like: “1010 0111 1010 0111 1010 0111 1010 0111 0000 1000”.

Basically they are saying that numbers that sound wobbly are better.

Lots more radio patterns can be found (and listened to) on this website.

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