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An antenna of 50 cm usable on 7MHz, inside or in little cleared zone?

The effectiveness of such an antenna is obviously definitely lower than a dipole correctly deployed and released in outside.

By taking the example of a dwelling not allowing the installation of antennas on the roof, it is nevertheless a means of making qso on HF band.

Several web sites approach already the theoretical aspect and one finds sufficient contradictory explanations on the subject.
Here thus a simple description of a realization practises which wants to be centered on the experimentation.