Receiver impedance matching circuit - uses transformer with tappings corresp. to different antenna impedances for corresp. frequency ranges

摘要

The receiver has an antenna covering at least two different frequency ranges, e.g. 0.15 to 1.605 MHz and 5.9 to 26.1 MHz. An impedance matching circuit used to match the antenna resistance to the wave resistance of a coupling line (A) comprises a transformer (U) with the same number of tap-off points, (1,2,3) as the number of different antenna impedances corresp. to the different frequency ranges. The different tappings (1,2,3) are coupled together and to the coupling line (A) via a selection network. The latter pref. comprises a capacitor (C1) for the highest frequency range and a coil (L1) for the lowest frequency range, with the adjacent arms exhibiting a resonance frequency between the two frequency ranges. The impedance matching circuit is simple and cheap.