US 4,241,451 A · Single sideband signal demodulator

Abstract

A single sideband signal can be demodulated by using sampled data techniques. An intermediate frequency (IF) radio signal is split into two branches and is sampled by two sample and hold devices; each sample and hold device operates at a rate that is not only a submultiple of the carrier frequency, but is also at least twice the information bandwidth. Prior to, or during sampling of one branch (the quadrature branch), a Hilbert's transform is performed upon the IF signal which results in the output of the two sample and hold devices being in phase quadrature. A phase shift of 90.degree., using a baseband finite impulse response Hilbert's transform filter, is performed upon the output signal of the quadrature branch's sample and hold device. The sum of the inphase sampled signal and the filtered quadrature phase sampled signal produces the demodulated lower sideband while the difference between the two produces the demodulated upper sideband. There are two basic examples shown of single sideband demodulation through the use of sampled data techniques; in addition, there are several examples of implementing the Hilbert's Transformer.

Claims13

Dependent claims

A demodulator for demodulating a received signal that can be represented by the equation Y(t)=X(t) cos (.omega..sub.c t+.phi.).+-.X(t) sin (.omega..sub.c t+.phi.) where .omega..sub.c is the carrier frequency and .phi. is a constant phase shift, comprising:

means for converting the received signal y(t) into a first baseband signal Y(nt.sub.s) where n is an integer variable and t.sub.s is a sampling period;
means for converting the received signal Y(t) into a second baseband signal Y(nt.sub.s);
where n is an integer variable and t.sub.s is a sampling period;
means for performing a Hilbert's transform on the second baseband signal Y(nt.sub.s) to obtain a quadrature second baseband signal Y(nt.sub.s);
means for adding the first baseband signal Y(nt.sub.s) to the quadrature second baseband signal Y(nt.sub.s) to obtain a lower sideband signal;
and
means for subtracting the quadrature second baseband signal Y(nt.sub.s) from the first baseband signal Y(nt.sub.s) to obtain an upper sideband signal.

4 more elements

In combination, a single sideband radio receiver for receiving a signal that can be represented by the equation Y(t)=X(t) cos (.omega..sub.c t+.phi.).-+.X(t) sin (.omega..sub.c t+.phi.) where .omega..sub.c is the carrier frequency and .phi. is a constant phase shift including, in cascade arrangement, an antenna, a filter and RF amplifier means, a mixer means, IF filter and amplifier means, a single sideband demodulator means, and a local oscillator means connected to said mixer means, wherein said single sideband demodulator means, comprises:

means for converting the received signal Y(t) into a first baseband signal Y(nt.sub.s) where n is an integer variable and t.sub.s is an sampling period;
means for converting the received signal Y(t) into a second baseband signal Y(nt.sub.s);
where n is an integer variable and t.sub.s is an sampling period;
means for performing a Hilbert's transform on the second baseband signal Y(nt.sub.s) to obtain a quadrature second baseband signal Y(nt.sub.s);
means for adding the first baseband signal Y(nt.sub.s) to the quadrature second baseband signal Y(nt.sub.s) to obtain an lower sideband signal;
and
means for subtracting the quadrature second baseband signal Y(nt.sub.s) from the first baseband signal Y(nt.sub.s) to obtain an upper sideband signal.

4 more elements

Dependencies are inferred from the claim text.

Single sideband signal demodulator

Life of this patent

Single sideband signal demodulator

Life of this patent

Abstract

Claims13