Robert E Kroll

US Patent:

44701489, Sep 4, 1984

Filed:

Oct 30, 1981

Appl. No.:

6/316716

Inventors:

Richard C. Mott - Gaithersburg MD
Robert T. Kroll - Middletown MD
Tsvi F. Assal - Bethesda MD

Assignee:

Communications Satellite Corporation - Washington DC

International Classification:

H04L 700

US Classification:

375113

Abstract:

A burst duration and guard space monitor circuit which produces burst duration and guards space signals which are substantially unaffected by nulls or near nulls in a received QPSK signal. The received QPSK signal is compared with a fixed threshold voltage. The comparison output is sampled at twice the symbol rate of the QPSK signal and the samples are first clocked into a three-bit burst duration shift register. The outputs of each of the cells of the burst duration shift register are OR'ed to produce the burst duration signal. The burst duration signal is inverted and then clocked into a four-bit guard space shift register, the outputs of which are OR'ed to produce the guard space signal. A clock signal is produced for operating the flip-flops, burst duration shift register and guard space shift register which has a frequency of twice the clock frequency of the QPSK signal. This clock signal is adjusted in phase so that the sampling times of the detected QPSK signal occur at times removed from nulls or near nulls therein.