1. A demodulator for demodulating radiofrequency signals, comprising:
a mixer, which downconverts the radiofrequency signal into an intermediate frequency range, the mixer generating an in-phase signal and also a quadrature signal,
a signal converter unit, which converts the in-phase signal and also the quadrature signal into an output signal of increased carrier frequency, the signal converter unit varying the sign of the output signal in a manner dependent on the product of the signs of the in-phase signal and of the quadrature signal, and
determining means for determining the period duration or the frequency of the output signal generated by the signal converter unit.
2. The demodulator as claimed in claim 1, wherein
the demodulator further comprises channel filters for the in-phase signal and the quadrature signal, which are connected downstream of the mixer and suppress, at least in part, frequencies outside the intermediate frequency range.
3. The demodulator as claimed in claim 2, wherein
the channel filters comprise complex bandpass filters.
4. The demodulator as claimed in claims 1, wherein
the signal converter unit comprises means for an XOR combination of the in-phase signal and of the quadrature signal.
5. The demodulator as claimed in claim 4, wherein
the in-phase signal and the quadrature signal are embodied as analog signals, and in that the means for the XOR combination of the in-phase signal and of the quadrature signal are embodied using analog technology.
6. The demodulator as claimed in claim 4, wherein
the signal converter unit comprises means for limiting and level matching of the in-phase signal and of the quadrature signal and in that the means for the XOR combination of the in-phase signal and of the quadrature signal are embodied using digital technology and combine the limited, level-matched signals.
7. The demodulator as claimed in claims 1, wherein
the signal converter unit comprises a multiplier stage for multiplying the in-phase signal and the quadrature signal, the in-phase signal and the quadrature signal being embodied as analog signals.
8. The demodulator as claimed in claim 1, wherein
the determining means for determining the period duration or the frequency comprises edge detectors for detecting the signal edges of the output signal of the signal converter unit.
9. The demodulator as claimed in claim 8, wherein
the determining means for determining the period duration or the frequency comprises edge detectors for detecting the rising signal edges and edge detectors and for detecting the falling signal edges.
10. The demodulator as claimed in claim 1, wherein
the determining means for determining the period duration or the frequency comprises at least one counting discriminator for detecting the time intervals between successive rising or falling signal edges.
11. The demodulator as claimed in claim 10, wherein
the at least one counting discriminator comprises a counter whose counter reading is counted up by a counting clock, the counter being read and reset with each pulse of the edge detector.
12. The demodulator as claimed in claim 1, wherein
the determining means for determining the period duration or the frequency comprises at least one integrator which integrates the output signal generated by the signal converter unit.
13. The demodulator as claimed in claim 1, wherein
the determining means for determining the period duration or the frequency comprises at least one conversion element, with which the detected period durations are converted into values proportional to the frequency.
14. A radio station, which comprises a demodulator as claimed in claim 1.
15. A method for demodulating radiofrequency signals, comprising:
a) downconverting the radiofrequency signal into an intermediate frequency range and generation of an in-phase signal and also of a quadrature signal;
b) converting the in-phase signal and of the quadrature signal into an output signal of increased carrier frequency, the sign of which is varied in a manner dependent on the product of the signs of the in-phase signal and of the quadrature signal; and
c) determining the period duration or of the frequency of the output signal.
16. The method as claimed in claim 15, wherein
the in-phase signal and the quadrature signal are converted into the output signal by means of an XOR combination.
17. The method as claimed in claim 15, wherein
the output signal is obtained by multiplication of the in-phase signal by the quadrature signal.
18. The method as claimed in claim 15, wherein
signal edges of the output signal are detected in order to determine the period duration or the frequency of the output signal.
19. The method as claimed in claim 18, wherein
the time intervals between successive rising or falling signal edges are detected in order to determine the period duration or the frequency of the output signal.
20. The method as claimed in claim 15, further comprising
integrating the output signal in order to determine the period duration or the frequency of the output signal.
21. The demodulator of claim 1, wherein the intermediate frequency range does not comprise the frequency of zero.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method of using a level meter employing the radar principle, serving to measure the fill level of a medium in a container and incorporating an electric conductor system for conducting an electromagnetic signal into the container and returning reflected components of the electromagnetic signal from the container, said electric conductor system terminating at a predefined fill level in the container, comprising utilizing a variation of the component of the electromagnetic signal that is reflected at the end of the electric conductor system as an indicator of whether the medium has reached said predefined level.
2. The method as in claim 1, including the step of configuring the electric conductor system as a dual-conductor assembly composed of the two conductors.
3. The method as in claim 2, including the step of providing the dual-conductor assembly with an open end.
4. The method as in claim 2 or 3, including the step of providing the ends of the two conductors with mutually different geometric configurations.
5. The method as in claim 4, including the step of extending the two conductors into the container to different depths.
6. The method as in claim 5, including the step of providing the dual-conductor assembly in the form of a coaxial cable, having a core conductor whose end protrudes or is recessed relative to the end of an outer conductor of the coaxial cable.
7. The method as in claim 1 or 2, including the step of utilizing for said variation a polarity reversal of said signal.