Unun vs. Balun

I think you could make a palindrome starting with with "Un balun y un unun..."  I don't think I'm the right man for that task. But I can tell you what they are and what they are for. balun is a difficult word to research being both a surname, an engineering term, a city,  and a slang word in Spanish meaning  balloon. They are both types of transformers and sometime I'll have to write a post about those as well.

• Balun [bal-uhn] noun

A device that allows a symmetrical antenna to feed an asymmetrical line. It is balancing an unbalanced input. It's a portmanteau word combining balanced and unbalanced. In it's early use it was almost always called a "balun transformer." We have largely dropped "transformer" from it's paired use. Balun already intimates transformer.  I hae fourd it used in catalogs from 1950, and it appears to have come into use in the decade prior.  The earliest use I found was in a 1947 catalog and was describing a "Balun bazooka" then described it as "a device for transforming from BALanced Line to UNbalanced."  [Their own capitalization] the timing leads me to believe that the contraction is military in origin. Here are a couple confirmed early uses:

Very High-Frequency Techniques, Vol. 1 - Harvard U. - 1947
"For a fixed position of the balun short-circuiting bar, the induced voltage E tends to increase with the frequency"

Hewlett-Packard Journal , Volumes 1-13 - H.P. Company  - 1949
"When this condition exists, there is theoretically no phase error introduced by deviations in balun legnth."

Radio Engineering - Terman, Frederick- Mcgraw-Hill - 1947
"At the same time, the balun does not introduce an unbalanced load to the balanced system, since the impedance across 2-3 approaches infinity..."

• Unun [uhn-uhn] noun

A device that allows an unbalanced antenna to couple with an unbalanced feed line. It's also a portmanteau word combining Unbalanced with Unbalanced. It's a less common device and more than likely a pun based on balun. This term has a much more recent vintage. I can't find it in any texts before about 1995. The earliest reference I found was in Issue 72 of the ARRL handbook for the radio amateur.

The humble toroid

I was asked months ago how a toroid removes noise from an audio cable. This is absurdly complicated so if the technical stuff eludes you, come back tomorrow. I'll avoid equations, but there is going to be some math.

In short, a toroid is a ferrite doughnut. Sometimes they are made of maganese-zinc alloy, or nickel-zinc. I can't really stop there because that wouldn't be interesting or arcane. So hold on to that doughnut idea. I'll come back to it. First we have to visit the 1800s long before Krispy Kreme.
In 1820 Hans Oersted discovered that electric currents can create magnetic fields in conductive material. Seems simple now, but this was hot news then. Andres Ampere got very excited about this. He began determining the relationship of electric currents to magnetic fields. Ampere went on to write a fundamental law of electromagnetism, Ampere's law states that the magnetic field around an electrical element is proportional to the electrical current that is it's source. This was groundbreaking and also happened to be wrong. He wasn't totally wrong, more incomplete. But he was wrong enough that there also exists an equation referred to by the catchy name of "Maxwell's correction to Ampere's law."

So in any circuit the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop. The magnetic field depends only on the amount of current enclosed by the loop and not on how that current is distributed. In other words, the magnetic field outside the wire depends on the amount of current, not on the diameter of the wire.

Regardless the equation governs the properties of a magnetic field in a solenoid (coil of wire) a straight wire, the field inside the wire and yes even the humble toroid. Yes, we're back to the doughnut now. It is a ring of ferrite, aka iron with wire coiled around it making an inductor. This is a resonant circuit because of its self-capacitance.

This inductor acts as though it includes a parallel capacitor, because of its closely spaced windings. These adjacent windings have different electrical potential, but also lie in each others magnetic fiends. These different potential behave like the plates in a capacitor and storing charge. (Storing charge makes it like a capacitor. ) In twisted pair cable the two currents, in the toroid are equal and opposite and therefore null themselves so no radiation takes place at the cable. The two wires are thus balanced. It becomes a balun. This is how it reduces RFI.