GB1424177A - Antenna circuits for use in portable transmitter/receivers - Google Patents

Abstract

1424177 Aerials STORNO AS 28 May 1974 [1 June 1973] 23494/74 Heading H4A The electrical length of a helical aerial 1, which may have capacitive top loading, is adjustable either by means of a ferromagnetic pin 4, Fig. 4, which is arranged in the lower end of the aerial, or by means of a variable capacitor 5, Fig. 5, which is shunted across a number of the lower end turns of the aerial. To enable operation in two separated frequency bands an additional tuning circuit is provided which may be switched either in parallel with a number of the lower end turns of the aerial, as shown in Figs. 4, 5, or, alternatively, in series with said turns, as shown in Fig. 7. The additional tuning circuit may comprise an inductor and a capacitor in series, either being variable. The switching may be effected electronically using a diode 13, Fig. 7, which may be rendered either conductive or non-conductive by means of a switch 14. In the series arrangement shown in Fig. 7, this results in either a short-circuit or an open-circuit being placed across the additional tuning circuit.