Auto-heterodyne receiver

1. A receiver circuit comprising a first signal input for a first input signal, a second signal input for a second input signal, a first signal output for a first output signal and a second signal output for a second output signal, characterized by a local oscillator, a quadrature modulator, a first mixer and a second mixer, wherein a first input of the quadrature modulator is connected to the first signal input and a second input of the quadrature modulator is connected to the local oscillator, wherein a first input of the first mixer is connected to the first signal input, a second input of the first mixer is connected to an output of the quadrature modulator and an output of the first mixer is connected to the first signal output, and wherein a first input of the second mixer is connected to the second signal input, a second input of the second mixer is connected to the output of the quadrature modulator and an output of the second mixer is connected to the second signal output.

2. The receiver circuit according to claim 1 further comprising a first analog-digital converter connected to the first signal output and a second analog-digital converter connected to the second signal output.

3. The receiver circuit according to claim 1 , wherein the local oscillator is designed to generate an oscillation having a frequency of less than 50 kHz, preferably of less than 25 kHz.

4. The receiver circuit according to claim 1 further comprising a control loop wherein the control loop is designed to adjust the frequency of the local oscillator.

5. The receiver circuit according to claim 1 further comprising an amplitude normalization unit either connected between the first signal input and the quadrature modulator or connected between the quadrature modulator and the second inputs of the first and second mixers and designed to output an input signal having an unknown input amplitude as an output signal having a predetermined output amplitude.

6. The receiver circuit according to claim 1 further comprising a transducer arranged upstream of the first and second signal inputs and designed to decouple a respective signal component of signals that are present at a first input and a second input of the transducer and to output said signal component to the first and second signal inputs of the receiver circuit.

7. The receiver circuit according to claim 6 , wherein the transducer is a directional coupler and designed to put a forward wave on a selected signal input of the first or the second signal input of the receiver circuit and to put a backward wave on a remaining signal input of the first or the second signal input of the receiver circuit.

8. The receiver circuit according to claim 1 , wherein a current transformer is arranged upstream of a selected signal input of the first or the second signal input of the receiver circuit, said current transformer being designed to transform a current into a voltage.

9. The receiver circuit according to claim 1 , wherein at least one of the first and second mixers has a low-pass filter at the output side.

10. A measuring device for measuring a phase shift between a first HF signal and a second HF signal, characterized by a receiver circuit according to any one of the preceding claims and a phase measurement unit that is connected to the first and the second signal output of the receiver circuit, said phase measurement unit being designed to determine a phase shift between a first AF signal at the first signal output and a second AF signal at the second signal output.