To receive shortwave stations well it is not enough to have a good antenna and a good receiver.
It is necessary that the coupling between the antenna and the receiver is good, and it depends not only on these two elements, but also on the frequency of the signal being received.
To adapt the coupling between the antenna and the receiver it is possible to use a pre-selector, which consists of a passive coupling circuit formed by coils and capacitors.
We describe in this article the assembly of one of them that can take advantage of variable capacitors taken from old tube receivers.
The circuit is shown in figure 1.
The assembly aspect, which also uses selector switches that can be leveraged from older devices is shown in figure 2.
The assembly can be installed in a plastic box for ease of use.
The coils consist of wire coils 28 or 30 with 10-turn turns.
The number of shots will depend on the number of key positions you can achieve for your project.
To use, simply tune to a station on your receiver and then adjust the key for better reception.
L1, L2 - Coils - see text
CV1, CV2 - variable capacitors - see text
Other Materials:
Ferrite rod, wires, welding, mounting box, etc.
