Abstract: A dual stage filter providing a relatively deep notch whose attenuation versus frequency curve is asymmetrical. The filter consists of a helical transmission line one end of which is connected to electrical ground. The opposite end is connected to a variable piston capacitor whose remaining end is also connected to ground. The ungrounded junction of these two components is connected to an input connector through a series capacitor. An identical circuit is arranged and connected to the output connector. These two circuits are isolated from each other by a conductive partition and housing. A series inductor connects the input and output connector. A matching capacitor is connected in parallel across a portion of the series inductor.

Abstract: A window-mounted antenna assembly has a capacitive connection through the window glass, one plate of the capacitive connection being formed as an area of a printed circuit board which is connected to a coaxial feed by soldering or the like. A shunt inductive circuit is printed on the printed circuit board and matches the coaxial feed to active elements of relatively long electrical length.

Abstract: A half-wave length communications antenna assembly especially adapted to be mounted on non-conductive surfaces, such as on a window of a vehicle. The antenna assembly desirably includes an electrically shortened half-wave inductively loaded radiating whip loaded at its base end by a loading capacitor plate to be fixed to a non-conductive surface. The whip is coupled through the non-conductive surface to a transmission line internally of the vehicle by a coupling capacitor plate which, with the loading capacitor plate, forms a coupling capacitor. A tuned circuit which is tuned to the nominal resonant frequency of the whip is connected to the coupling capacitor plate and serves as an impedance matching circuit between the half-wave whip and the transmission line. The tuned circuit also affects the radiation pattern of the whip to produce a pattern more typical of a five-eighths wave length antenna to provide somewhat greater gain.