Magnetojector (INS047E)

The circuit shown generates a signal which is applied to a coil, from which it can be radiated to a test circuit.

The signal creates a low frequency field that can be picked up by transducers and inductive components without connection such as pickup coils, recorder heads, microphones and others, as shown in Figure 1.

Figure 1 - Applying the signal

How it works

The circuit consists of a simple audio oscillator with complementary transistors where the frequency is determined by the setting of P1 and the value of the capacitor C1.

The circuit load is not a loudspeaker, but a coil that can be wound on a nail or a screw with thin wire (28 to 32).

They are wound from 50 to 100 turns of the indicated wire.

The signal generated is rich in harmonics, which can excite both audio and RF circuits.

This allows tests on several circuits to be made, with direct pickup in cases of receivers or other more sensitive circuits.

Circuit power can be supplied with 2 or 4 small batteries.

Assembly

In Figure 2, we give the complete diagram of the injector.

Figure 2 - Circuit diagram of the magnetojector

As it is a very simple assembly, even an assembly on a terminal strip, as shown in Figure 3, is possible.

Figure 3 - Terminal strip assembly

For a more elaborate assembly we have a printed circuit board which is shown in Figure 4.

Figure 4 - Printed Circuit Board

Observe the positions of the transistors in the assembly.

In Figure 5, we have details of the construction of the transducer.

Figure 5 - The transducer

The resistors are 1/8 W and the capacitor can be ceramic or polyester.

A power supply for the circuit.

Figure 6 - A power source for the injector

To test, simply connect and approach the injection coil of an AM radio tuned out of station.