GB1320909A - Aerial arrangements - Google Patents

Abstract

1320909 Aerial coupling arrangements; transistor amplifying circuits PLESSEY CO Ltd 25 Aug 1970 [29 Aug 1969] 43031/69 Headings H3T and H4A An aerial whose effective length is shorter than one eighth wavelength at the highest operating frequency of the aerial arrangement is connected to amplifying means which is provided with a negative feedback circuit, and which is arranged to have an input impedance over the operating band that is greater than the effective source impedance of the aerial. As described, a short monopole aerial (e.g. one foot or less for the 10 kHz to 30 MHz band) is provided with a capacitive top, which effectively doubles its height, and is mounted on a buffer amplifier carried on a post extending from the ground (Fig. 1, not shown). Input from the aerial is coupled by a capacitor C 3 to one gate G 1 of a dual-gate MOST (metal oxide silicon transistor) M 1 , the other gate G 2 being biased by means of resistors R 4 , R 5 , and decoupled to the source electrode by a capacitor C 4 . A boot-strapping technique is used for biasing the gate G 1 , in which a resistor R 3 is connected at one end to said gate, and is connected at the other end to the output through a capacitor C 2 , and directly to the junction of two bias resistors R 1 , R 2 . The MOST M 1 is provided with a drain resistor R 6 from which output is taken to a bipolar transistor T 1 , the collector of said transistor T 1 being coupled to the source electrode of the MOST M 1 so as to complete a closed negative feedback path. The MOST M 1 and the transistor T 1 are biased by means of a third transistor T 2 , which is connected to form a direct current sink. Two relatively reversed paralleled diodes D 1 , D 2 are connected between the input and the output of the amplifier, to provide protection against high voltages due, for example, to static.