Stereophonic fm receivers having decoders employing field effect transistors

Claim 2

In an FM receiver adapted to receive a composite signal containing a monophonic signal (L + R), a pilot carrier and the sideband frequencies of a carrier suppressed carrier amplitude modulated by an L - R signal, said suppressed carrier being of a frequency harmonically related to the frequency of said pilot carrier, and to separate L and R audio frequency signals from said composite signal, a decoder adapted to switch automatically from a monaural operating condition to a stereophonic operating condition when a signal containing said pilot carrier and of a minimUm predetermined strength is being supplied thereto and also adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal containing said pilot carrier and of a strength lower than a minimum predetermined strength is being supplied thereto, said decoder also being adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal that is without said pilot carrier is being supplied thereto, said decoder comprising means responsive to said receiver receiving said composite signal at a strength above a minimum predetermined strength for providing a switching signal at a frequency corresponding to an integral multiple of the frequency of said pilot carrier, two junction field effect transistors each have gate, input and output electrodes, means connecting capacitors in circuit between said means for providing said switching signal and said gate electrodes for charging of said capacitors by said switching signal, resistors connected in shunt with said capacitors, and means for applying said composite signal to said input electrodes of said field effect transistors when said composite signal is received by said receiver at a strength above a minimum predetermined strength, said receiver including right and left audio signal output terminals, means connecting said output electrode of one of said transistors and one of said output terminals and means connecting said output electrode of the other of said transistors and the other of said terminals.

Claim 3

The invention according to claim 1, wherein said means for providing said switching signal includes a sub-carrier regeneration system having a transformer with a secondary winding across which said switching signal is developed.

Claim 4

The invention according to claim 2, wherein said winding has first and second terminals and a center tap therebetween, one of said capacitors being connected between said first terminal and said gate electrode of one of said transistors and the other of said capacitors being connected between said second terminal and the other of said transistors.

Claim 5

The invention according to claim 3 including means grounding said center tap.

Claim 6

The invention according to claim 3 including means for applying to said center a DC potential for reverse biasing said transistors.

Claim 7

The invention according to claim 2, wherein said sub-carrier regeneration system is a frequency doubler.

Claim 8

The invention according to claim 1, wherein said means for applying said composite signal to said input electrodes comprises an amplifier having a high output impedance and wherein said resistors have a high impedance.

Claim 9

In an FM receiver adapted to receive a composite signal containing a monophonic signal (L + R), a pilot carrier and the sideband frequencies of a carrier suppressed carrier amplitude modulated by an L - R signal, said suppressed carrier being of a frequency harmonically related to the frequency of said pilot carrier, and to separate L an R audio frequency signals from said composite signal, a decoder adapted to switch automatically from a monaural operating condition to a stereophonic operating condition when a signal containing said pilot carrier and of a minimum predetermined strength is being supplied thereto and also adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal containing said pilot carrier and of a strength lower than a minimum predetermined strength is being supplied thereto, said decoder also being adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal that is without said pilot carrier is being supplied thereto, said decoder comprising means responsive to said receiver receiving said composite signal at a strength above a minimum predetermined strength for providing a switching signal at a frequency corresponding to an integral multiple of the frequency of said pilot carrier, said means for providing said switching signal including a sub-carrier regeneration system having a transformer with a secondary winding across which said switching signal is developed, said secondary winding having a center tap, two junction field effect transistors each having gate, input and output electrodes, means connecting a capacitor in circuit with said center tap for charging of said capacitor by said switching signal, a resistor connected in shunt with said capacitor, means connecting said secondary winding and said gate electrodes, and means for applying said composite signal to said input electrodes of said field effect transistors when said composite signal is received by said receiver at a strength above a minimum predetermined strength, said receiver including right and left audio signal output terminals, means connecting said output electrode of one of said transistors and one of said output terminals and means connecting said output electrode of the other of said transistors and the other of said terminals.

Claim 10

In an FM receiver adapted to receive a composite signal containing a monophonic signal (L + R), a pilot carrier and the sideband frequencies of a carrier suppressed carrier amplitude modulated by an L - R signal, said suppressed carrier being of a frequency harmonically related to the frequency of said pilot carrier, and to separate L an R audio frequency signals from said composite signal, a decoder adapted to switch automatically from a monaural operating condition to a stereophonic operating condition when a signal containing said pilot carrier and of a minimum predetermined strength is being supplied thereto and also adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal containing said pilot carrier and of a strength lower than a minimum predetermined strength is being supplied thereto, said decoder also being adapted to switch automatically from said stereophonic operating condition to said monaural operating condition when a signal that is without said pilot carrier is being supplied thereto, said decoder comprising means responsive to said receiver receiving said composite signal at a strength above a minimum predetermined strength for providing a switching signal at a frequency corresponding to an integral multiple of the frequency of said pilot carrier, said means for providing said switching signal including a sub-carrier regeneration system having a transformer with a secondary winding across which said switching signal is developed, said secondary winding having a center tap, two junction field effect transistors each having gate, input and output electrodes, means connecting a capacitor in circuit with said center tap for charging of said capacitor by said switching signal, a resistor connected in shunt with said capacitor, means connecting said secondary winding and said gate electrodes, and means for applying said composite signal to said input electrodes of said field effect transistors when said composite signal is received by said receiver at a strength above a minimum predetermined strength, said receiver including right and left audio signal output terminals, means connecting said output electrode of one of said transistors and one of said output terminals and means connecting said output electrode of the other of said transistors and the other of said terminals.

Claim 11

The invention according to claim 8 wherein said capacitor is connected between said center tap and a grounded terminal.

Claim 12

The invention according to claim 8 wherein said capacitor is connected between said center tap and a terminal at a DC potential that reverse biases said transistors.