Linear monopole antennas are very easy to reason about.
Imagine (or actually draw) a sine wave graph, and then fit your antenna along the X axis of the graph. Now look at "signal" amplitude at the antenna's extremities. You'll notice that 1/4 wavelength antenna will give you the strongest signal, while 1/2 and full wavelength will apparently give no signal at all. The only reason that full-wavelength piece of wire picks up anything at all are build imperfections - wire length not perfectly matched to wavelength, not perfectly straight, not perfectly aligned with signal source, signal reflections hitting it from different angle, etc. Thats why olympus refers to performance of full-wavelength piece of wire as "random piece of wire"-kind of performance.
On the other hand, linear dipole would be 1/2-wavelength (or 2 times 1/4-wavelength), as it is just two 1/4-monopoles put together.
Imagine (or actually draw) a sine wave graph, and then fit your antenna along the X axis of the graph. Now look at "signal" amplitude at the antenna's extremities. You'll notice that 1/4 wavelength antenna will give you the strongest signal, while 1/2 and full wavelength will apparently give no signal at all. The only reason that full-wavelength piece of wire picks up anything at all are build imperfections - wire length not perfectly matched to wavelength, not perfectly straight, not perfectly aligned with signal source, signal reflections hitting it from different angle, etc. Thats why olympus refers to performance of full-wavelength piece of wire as "random piece of wire"-kind of performance.
On the other hand, linear dipole would be 1/2-wavelength (or 2 times 1/4-wavelength), as it is just two 1/4-monopoles put together.