Indoor unit of receiver for broadcasting satellite

• US 4,556,988 A
• Filed: 09/27/1983
• Issued: 12/03/1985
• Est. Priority Date: 09/27/1982
• Status: Expired due to Fees

• Current Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Yoshisato, Akiyuki
• Primary Examiner(s): NG, JIN FAY
• Application Number:
  US06/536,355
• Time in Patent Office: 798 Days
• Field of Search: 455/131, 455/182, 455/183, 455/189, 455/192, 455/207, 455/208, 455/209, 455/214, 455/260, 455/263, 455/314-316, 455/302, 329/122, 331/22, 358/188, 358/195.1
• US Class Current: 455/182.2
• CPC Class Codes: H03D 3/242 combined with means for controlling the frequency of a further oscillator, e.g. for negative frequency feedback or AFC
• CPC Class Codes: H03J 7/065 the counter or frequency divider being used in a phase locked loop

Abstract

Improved AFC performance is achieved in a satellite dish receiver by using an indoor unit having a first intermediate frequency (IF signal) which does not include an image frequency and by using a PLL-demodulator for controlling the AFC loop.

Claims

1. An indoor unit of a receiver which receives radio waves transmitted from a broadcasting satellite and group-converts the received radio waves into a first intermediate frequency signal which is then fed to said indoor unit for conversion into a second intermediate frequency signal;

the indoor unit having a single superheterodyne structure comprising;

a mixer for converting the first IF signal into the second IF signal;

a first VCO coupled to and driving the mixer;

an IF amplifier for coupling the second IF signal out from the mixer;

a PLL demodulator having a phase comparator, a loop filter and a second VCO, wherein a first portion of the VCO output is coupled to the phase comparator, and the input of said PLL demodulator is coupled to the IF amplifier output; and

an AFC circuit coupled to a second portion of the output of said second VCO and generating a control signal for controlling the frequency of the first VCO;

wherein the frequency of said second IF signal is selected sufficiently high so that an image frequency thereof is not included within the receiving range of the IF amplifier and a prescaler for dividing the second portion of the output of said second VCO, the prescaler being interposed between the output of the second VCO and the AFC circuit and supplying a divided-down signal to said AFC circuit.

2. An indoor unit of claim 1 wherein said AFC circuit comprises an FM detector, an integration circuit/amplifier coupled to the FM detector, and a reference signal oscillator coupled to the integration circuit/amplifier.

3. An indoor unit of a receiver which receives radio waves transmitted from a broadcasting satellite and group-converts the received radio waves into a first intermediate frequency signal which is then fed to said indoor unit for conversion into a second intermediate frequency signal;

the indoor unit having a single superheterodyne structure comprising;

a mixer for converting the first IF signal into the second IF signal;

a first VCO coupled to and driving the mixer;

an IF amplifier for coupling the second IF signal out from the mixer;

a PLL demodulator having a second VCO, where the input of said PLL demodulator is coupled to the IF amplifier output; and

an AFC circuit coupled to the output of said second VCO and generating a control signal for controlling the frequency of the first VCO;

wherein the frequency of said second IF signal is selected sufficiently high so that an image frequency thereof is not included within the receiving range of the IF amplifier;

the indoor unit further comprising a prescaler for dividing the output of said second VCO, the prescaler being interposed between the output of the second VCO and the AFC circuit and supplying a divided-down signal to said AFC circuit through an attenuator.