Antenna system using antenna base impedance transforming means
First Claim
1. In combination with an AM and FM broadcast receiver having a common antenna, said antenna having a relatively high capacitance reactance as a source at AM broadcast frequencies and having a relatively low impedance as a source at FM broadcast frequencies, said antenna being connected with said receiver for both AM and FM signals, impedance transforming means having an input connected with said antenna and having an output connected with the receiver said impedance transforming means comprising a field effect transistor amplifying device connected in a common drain configuration thereby applying an output voltage thereof as a negative feedback voltage to said input, and a capacitor effectively connected across said output to produce a feedback voltage substantially 180°
- out of phase with the voltage in the antenna at AM broadcast frequencies whereby substantially 100% degeneration is produced.
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Abstract
An antenna system is disclosed for plural band radio receivers having a common antenna. The system is especially adapted for AM/FM automobile broadcast receivers and may be used with a CB transceiver with a tri-band antenna. An impedance transforming means is provided at the base of the antenna and a single transmission line or lead-in cable extends from the impedance transforming means to the AM/FM receiver. The impedance transforming means has a high input impedance for the AM and FM bands and a relatively low output impedance to minimize the signal loss in transmission from the antenna to the receiver. The impedance transforming means includes a field effect transistor in a common source configuration and means are provided to produce substantially 100% voltage degeneration for both AM and FM signals. The impedance transforming means is also useful for automobile AM broadcast receivers to avoid the need for alignment of the antenna trimmer after installation of the antenna and lead-in cable on the automobile.
31 Citations
12 Claims
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1. In combination with an AM and FM broadcast receiver having a common antenna, said antenna having a relatively high capacitance reactance as a source at AM broadcast frequencies and having a relatively low impedance as a source at FM broadcast frequencies, said antenna being connected with said receiver for both AM and FM signals, impedance transforming means having an input connected with said antenna and having an output connected with the receiver said impedance transforming means comprising a field effect transistor amplifying device connected in a common drain configuration thereby applying an output voltage thereof as a negative feedback voltage to said input, and a capacitor effectively connected across said output to produce a feedback voltage substantially 180°
- out of phase with the voltage in the antenna at AM broadcast frequencies whereby substantially 100% degeneration is produced.
- View Dependent Claims (2, 3, 9, 10)
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4. In combination with a receiver adapted for reception of a given frequency band, an antenna having a capacitive reactance at said frequency band, an impedance transforming means having an input connected to the antenna and having an output connected to the receiver, said impedance transforming means comprising an amplifying device having an output voltage and connected in a configuration having a common electrode circuit arranged so the output voltage is applied as a negative feedback voltage to the input of the device, and phase shift means in the output of said impedance transforming means for producing a feedback voltage substantially 180°
- out of phase with the voltage induced in the antenna at frequencies in said given frequency band to produce approximately 100% degeneration.
- View Dependent Claims (5, 6, 7, 8, 11, 12)
Specification