Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Patent
1998-06-11
2000-12-12
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
331176, 331 10, 455260, H04B 106
Patent
active
061610038
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to the field of radio signal transmission characterized by coherent demodulation, and specifically to a process and device for automatic local oscillator frequency stabilization in radio receivers employing a wide-band tunable local dielectric-resonator oscillator.
Coherent demodulation is used in a large part of both public and private professional transmission systems, among which an important place is reserved certainly for microwave radio links and satellite communications systems.
FIG. 1 shows a typical block diagram for a transmitter and a receiver connected to the same antenna and which find use in the above mentioned professional systems. The diagramming is quite general and can represent any system, whether analog or digital, characterized by coherent demodulation.
With reference to FIG. 1 there is seen a block 1 at whose input arrives a base band signal S.sub.T to be transmitted. The signal S.sub.T is in most cases a complex signal obtained by appropriately multiplexing multiple elementary signals coming e.g. from multiple telephone channels. To maintain greater generality in the discussion, in FIG. 1 a multiplexing block for these channels is not shown. The block 1 comprises circuits which perform on the signal S.sub.T known operations such as, for example, filtering and which are preliminary to the modulation operations of a carrier, frequency conversion and subsequent transmission. The signal from block 1 reaches a first input of a modulator 2 which uses the input signal as a modulating signal for an intermediate frequency oscillation f.sub.i present at a second input of this block. The modulated signal from block 2 reaches in turn an input of a frequency converter 3 (up-converter) to which arrives also a frequency oscillation f.sub.olt generated by a local transmission oscillator 4. The block 3 converts this modulated signal into a radiofrequency transmission signal. The signal from block 3 is amplified by a linear radiofrequency power amplifier, represented by block 5, and then coupled to a first gate of a directional coupler represented by block 6. A second gate of the directional coupler 6 is coupled to an antenna 7 while a third gate thereof is coupled to a radiofrequency receiving amplifier 8 characterized by low noise-figure value. On the paths from block 5 to block 6 and therefrom to block 8 are respectively inserted a band-pass transmission filter and a band-pass receiving filter, not shown in the figure, generally with different center-band frequencies.
The directional coupler 6 and the respective filters (duplexers) allow radiation by the antenna 7 of the transmission signal without disturbing the reception path and simultaneous correct routing of a receiving signal received by the antenna 7 toward the amplifier 8. The signal from the amplifier 8 reaches an input of a second frequency converter 9 (down-converter) to which also arrives a frequency oscillation f.sub.olr generated by a local receiving oscillator 10. The block 9 converts to intermediate frequency f.sub.i the radiofrequency receiving signal present at its own input. The signal from block 9 reaches a demodulator 11 which returns it to base band, utilizing for this purposes an intermediate frequency carrier reconstructed locally starting from the carrier data contained in the signal from the converter 9, after appropriate intermediate frequency filtering by a filter not shown in FIG. 1.
The base-band signal at the output of the demodulator 11 reaches a block 12 which performs on the signal known operations designed to restore a received signal S.sub.R which is a faithful copy of the signal S.sub.T originally transmitted. By analogy with the above remarks concerning the signal S.sub.T, the signal S.sub.R must be demultiplexed into the individual component signals. Again in this case, to maintain greater generality in discussion, a demultiplexing block for these signals is not shown, while for the sake of simplicity a processing block which keeps the operation of the various blocks
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De Marzi Giuseppe
Dimonte Giuseppe
Lo Curto Michelangelo
Eisenzopf Reinhard J.
Italtel SpA
Mehrpour N.
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