This is an interesting FM (broadcast / receive) Antenna ... seems ok, but I'm a bit
puzzled over the longer lengths that could be used.
I'm more than a bit puzzled over ANY of the lengths he used.
His antenna is NOT 5/8 wave, and even a 5/8 wave folded dipole isn't going
to work particularly well. Yes, I'm sure it will pick up some RF, and perhaps
more so that a standard whip, but you might as well choose any other random
length in that case.
A folded dipole should be a half wavelength. Since 100 MHz = 3m wavelength,
this will be very close to 1.5m, and this value is probably adequate to cover the
band without any further adjustment.
Doubling the length and using a folded dipole on its second harmonics is NOT
a good idea: the currents are out of phase in the two wires, so it takes a
lot of total current to get any effective radiation.
If you want a longer antenna, then an Extended Double Zepp might be a good
choice: use regular wire for the radiator (not
a folded dipole). The
total length is about 1.25 * the wavelength, so 3.75m, or say 1.85m on
either side of the feedpoint. This will have more directivity, so it should
be installed broadside (at right angles to) the incoming signal.
Your current loop (assuming it is in the vertical plane rather than horizontal)
will outperform his recommended antenna. And probably more so for his
If you need more gain that that, there are several possibilities depending on
the space you have available: a 2-element quad, a yagi, various sorts of
colinear, broadside or end-fire arrays, or even a vee-beam or rhombic.