I would like to know whether a loading coil antenna can be used for receiving HF signals, especially for the SW broadcast?
Usually, any HF resonant antenna would be too long but can a shorter whip antenna with a loading coil be used for HF reception?
I want to connect that loading coil antenna with the whip anyenna of the radio using an alligator clip.
Yes, it can be used, but the picture you depicted misses a few key points.
For a receive antenna, there is little advantage in using a loading coil. That does not enhance the ability to catch weak signals.
The advantage of using an external antenna is that you can put the antenna outside your house, where the signal is stronger. A part of this advantage is that the antenna is farther from noise sources, like your home's power lines in your walls and all sorts of devices (switching power supplies, inverters, LED lights, etc.).
In HF, the ability to receive weak signals is largely determined by the ratio of the signal power to the ambient noise power.
So, the loading coil would influence the signal and noise power to the receiver equally. That is why it is not worth the effort. The best place to use effort is to place the antenna away from the noise sources and in places with a better view of the sky near the horizon.
Another missing piece is the radial or counterpoise. You'll need a radial wire where the antenna connects to the coax. I would not connect it to the building structure or wiring/piping used for other purposes, as it is likely to pick up more noise.
Instead of a whip, you could use a wire of any reasonable length.
If your radio receiver has insufficient sensitivity, you could get an active (amplified) antenna.
Another missing piece is the coax braid on your radio side. Even if you use a coax, if the braid is not connected to the radio receiver's RF ground, it does not function as a coax; it's just a wire. So, the "coax" will serve as the antenna, picking up the nearby noise. You don't want that. If your radio does not have a proper antenna input connector, you may have to figure out where you can connect the coax most effectively.
