(I promise there will be a question in this wall of text. I'm just giving context.)
I've been wanting to try my hand at building my own antenna system for the last few weeks and in doing research, a number of questions came up. In particular, matching transmitters, feed lines and antennas in order to create a fully balanced system.
This site, run by W5ALT, gives a great overview on why different systems need to be impedance matched in order to function properly, as well as consequences of improper impedance matching. I therefore understand why a balun would be used for coax feeding a balanced dipole, both for balance and impedance purposes.
I also went about researching different antennas for portable use. Stackexchange led me to the October 1984 QST article on a full-wave delta loop. One of these setups (see following image, part B) describes a 450-ohm ladderline going into a 100-ohm feed point on the loop.
On this site, the author says to NOT use a balun between the 50- or 75-ohm coax feedline and the 100-ohm feed point:
Don't use a Balun on this Antenna! On a horizontally oriented loop you can feed a corner, center of a side or anywhere it is unimportant.
I also have a folded dipole fed directly by ladderline (Cobra Ultralite Sr.) that functions quite well (I busted through a pileup for a Portuguese contest; it can't be that bad). It is fed by 50-ohm coax from a tuner into a 1:4 balun to the ladderline. From various sources on the internet, the typical impedance of a resonant dipole is roughly 73 ohms. A folded dipole will increase this impedance to the square of the number of parallel elements (for the ultralite sr. with 3 parallel elements, I calculate 9 * 73 = 657 ohms impedance). The feedline could very well be 600-ohm ladderline (I am not sure; the line is not marked with impedance).
So my question is this: in particular, why does the W1FB full-wave loop design not require some form of a transformer between the 450-ohm ladderline and the 100-ohm antenna? My research tells me it's obvious that having matched impedance would allow more efficient power transfer from the feedline to the antenna. Is it because ladderline is balanced? Is that kind of impedance mismatch allowable? Is it a rule that you don't need a balun for ladderline? Is it purely a choice by the designer? I'm familiar with the subject of electronics, but I'm certainly no electrical engineer, so the theory behind this just seems to contradict practical examples.
Thanks for any and all help. I've been trying to find a reason for this for days and nothing seems logical to me.