I can add a little information that might be helpful.

When considering a receiving antenna, the single thing you need to be
concerned about is signal to noise ratio. Unless your antenna is
exceptionally poor and/or your receiver exceptionally noisy, making what
you receive louder is just a matter of turning up the volume, or adding
an audio amplifier if it's not loud enough. But it won't help you hear a
station, because it and the noise will get louder in the same proportion.

Quite a bit of what you'll read about antennas deals with improving
antenna efficiency. That's because it's important when the antenna is
used for transmitting. But when you use it for HF receiving, efficiency
doesn't matter unless it gets to be bad enough that your receiver's
noise becomes greater than the atmospheric noise it's receiving. A quick
test for this condition is to disconnect the antenna. If the noise
decreases, it means that atmospheric noise is greater than receiver
noise -- the usual case -- and efficiency improvements won't help any.
They'll just increase both the signal and noise by the same amount,
which won't help you a bit in hearing any signals.

To improve reception, you have to improve the signal to noise ratio. If
there's noise coming from a local source, for example a light dimmer or
an arcing power line, you can often reduce the noise by using a
horizontal antenna, putting the antenna away from the house and power
line conductors, and making sure the feedline is decoupled so it isn't
part of the antenna. If noise is mostly coming from a single direction,
either local or distant, an antenna with a sharp null such as a small
rotatable loop often helps. And, other rotatable antennas with a
directional pattern such as Yagis and log periodics, will help if the
signal and at least some of the noise are coming from different
directions. If a fixed antenna is on the order of a half wave or longer,
you might get lucky and have a null pointed at a noise source. The null
will usually change direction with frequency, though, so it'll likely
only do the trick over a narrow range of frequencies. This can actually
be a bad thing, because when somebody gets lucky like this, he'll often
tout the antenna as being nearly miraculous in its performance, but no
one else will be able to duplicate the results.

Enjoy your shortwave listening. It's how I and probably most amateurs
got started in this fascinating hobby.

Roy Lewallen, W7EL