Where did you see those quotes? I know there are a few odd statements in Baluns and UN-UNs, but where did that come from??
I don't think we can say the core 100% conveys power is ANY transformer with interleaved windings. But where there is core magnetization, we must pay attention to core flux density and core loss tangent.
In other words when we need a core in a system, we have to be careful what we use no matter what the system.
Are those quotes from UnUns and Baluns??
Those quotes are not from UnUns and Baluns; they are from a publicly available tutorial on the web. The third quote was contained in a private eMail from the author to me:
The beauty of impedance transformation by series/parallel wiring of common mode chokes (the Guanella balun) is that they do NOT put differential flux in the core like a voltage balun.
The author appears not to frequent this forum, so I'm trying to be fair and preserve his anonymity; although at least one reader has already worked it out! My purpose in posting originally was not to embarrass the author - rather it was to test my own ideas in a wider forum at a point where he no longer wished to discuss the issue until I had "studied the fundamentals".
Here's my simplistic "take" on that last quote: I wind three identical common mode chokes - same wire, same turns, same cores - and I use two of them in a 4:1 Current Balun and the other one in a 4:1 Voltage Balun. Fig 1 and Fig 2 here:http://www.karinya.net/g3txq/temp/4%20to%201%20current%20balun%207.jpg
The core flux and losses are related directly to the common-mode voltages Vcm1, Vcm2 & Vcm3. Then, trying different load-balance conditions:
Load floating: Vcm1 = Vcm2 = Vin/2, Vcm3 = Vin
Balanced load (point C ground): Vcm1 = 0, Vcm2 = Vin, Vcm3 = Vin
Unbalanced load (point A ground): Vcm1 = -Vin, Vcm2 = 2.Vin, Vcm3: N/A Balun Input short-circuited
Unbalanced load (point B ground): Vcm1 = Vin, Vcm2 = 0, Vcm3: N/A choke output short-circuited
So, taking as a reference the losses in the voltage balun with a floating load or balanced load, the losses in the current balun might be anywhere from half to 5 times that, depending on the load configuration. I realise that those extreme load configurations are unlikely to be encountered in practice, but I believe they serve to illustrate the principle.
Please don't think I'm advocating the use of a voltage balun over a current balun - I'm not! There are good reasons to choose the 4:1 current balun over the 4:1 voltage balun in many situations, but that quote is not one of them!