Below is a superimposed version of the plot of SWR for a series of 44 frequencies (that I keep in a file for frequent use) to cover the ham band frequencies. The dots on the plot are the discrete frequencies where model calculations are done. The pink plot shows the SWR results for a 300-ohm source connected to one corner of the loop. The blue plot represents a 450-ohm source. Click on the plot to expand the view.
The combined plot shows that the 300-ohm source gives slightly lower SWR on the lower bands (80 and 40 m) while the 450-ohm source gives slightly better SWR on the high bands. (60 m is, of course, the odd-ball.) The differences in SWR are not too significant and either case should be manageable by a decent antenna tuner.
Additional analysis can include a selected length of feedline from the loop to the source (transmitter). The impedance seen at the transmitter end will likely be transformed to a value different from what is seen at the loop's feed point. We know that odd multiples of 1/4 wavelength will transform impedance from low to high or vice versa, while even multiples will present an unchanged impedance at the transmitter. Other lengths will present some other impedance. With some care in feedline length selection we will (hopefully) avoid extreme values of impedance at the transmitter end.
