To understand this we need to tighten some physical things. This antenna is based on the electrical signal-field in the air.
We must realize that in the city, and in our homes, we live between incredibly strong electro-magnetic radiation from our (DECT) phone, computer, baby monitors, power supplies, fluorescent lamps, WiFi, and various other devices indoors. So we live in a fairly strong electromagnetic field radiation, which prevents other weak RF signals from outside, can not be received by the strong radiation field. They are there, but are ‘pushed’ by the stronger radiation inside our house. An amplifier does not make sense for these weak signals, because the strong interior radiation strengthens it, and make matters worse.
In other words, the strong radiation field in a house has a high noise value, and the weak RF signals that we want to receive a lower noise value. In this low noise RF amplifier is NOT above the strong noise indoors, so we will not hear the weak RF signals in our receiver. The only way to solve this is to find a solution to reduce the strong noise, until our receiver also will be able to receive the weak RF signals enough. Of these, a number of physical measurements have been made, with surprising results.
Most of them do know that there exist two types of antennas: one type (most window antennas) received best at the electric field in the air, and the other kind of antennas (usually loop-antennas), received on the best magnetic field in the air. Now bring the measurements somewhat surprisingly to light. Magnetic (loop) antenna, interior posted receives LOTS of interference inside the house, but can still somewhat works, because this antenna must be sharply tuned in (a capacitor) to a narrow frequency band. But that is not really suitable for HF broadband reception. Window antennas, have not these capacitors, and received interior the full distorsion over the entire HF band. But now it comes. In various measurements of magnetic and electric fields inside and outside, it has been found that the magnetic fields remain mostly within our homes, through the walls and the like, and that the electric fields are less affected by that. This means that we outsite, on a certain distance from our house, much better RF signals can be received, and the interference radiation from the house though it will reduce a lot. This makes the application of a window-antennas outside of a lot better. A wire, as well as window-antenna behaves primarily as a capacity on the lower frequencies. .
Now this science is known, this is also applicable to a “whip” antenna, both active or not. And it will also receive the electric field from the air. Now it is known, is one to look for other types of antenna.
It appeared that a small whip antenna works mostly capacitive. That gives temptation to replace the rod by a “capacity” or simply a (copper) surface. And it works! And so was born the Mini Whip antenna,
Although there of the “whip” not much is left. But the name Mini “Whip” remained.
A disadvantage could be that now the active part of the antenna, the copper surface is very small, so abbreviated.
So the signals were coming up here very, very small. And that’s actually true. However, we use a FET transistor which is very sensitive to small signals. And it works, as long as the interference radiation of the environment is small enough. Measurements have shown that the best best RF reception is approximately 100 meters from buildings. But that is absurd. Most of us will not get. However, it has already proved it is possible from a few meters of building HF reception ! How further the distance the better. Please note that the antenna should not be placed on the end of a metal tube.
In the construction set are no major problems. My first copy is made entirely of parts from the junkbox ! The antenna cable is 10 meters using 50 ohm (RG-58U) coaxial cable. Any other coax cable is fine.