Superheterodyne SCA receiver and method for the manufacture thereof

• US 5,023,933 A
• Filed: 10/13/1988
• Issued: 06/11/1991
• Est. Priority Date: 10/13/1988
• Status: Expired due to Fees

• Current Assignee: Frank P. Jr. Karkota
• Original Assignee: Frank P. Jr. Karkota
• Inventors: Karkota, Frank P. Jr.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): URBAN, EDWARD F
• Application Number:
  US07/257,512
• Time in Patent Office: 971 Days
• Field of Search: 455/45, 455/206, 455/214, 455/200, 455/266, 455/339, 455/307, 333/178, 370/110.4
• US Class Current: 455/45
• CPC Class Codes: H04B 1/1646 adapted for the reception of stereophonic signals
• CPC Class Codes: H04H 20/34 using an out-of-band subcarrier signal
• CPC Class Codes: H04H 40/18 Arrangements characterised by circuits or components specially adapted for receiving

Abstract

An SCA receiver is provided which has a close to ideal passband characteristic which greatly improves frequency response to produce a brighter sound due to the use of ceramic resonator elements. The use of ceramic resonator elements and a superheterodyne approach also provides a receiver which can be rapidly aligned and which has improved noise protection, lower distortion, increased stability, less residual subcarrier in the audio, and more consistent performance from one unit to the next. In one embodiment the superheterodynes circuit operates at 455 kHz which up-converts the usual 67 kHz signal by mixing it with the output of a ceramic resonator controlled local oscillator/mixer. The ceramic resonator and ceramic filter along with the local oscillator/mixer I.C. provides low group delay, improved impulse noise rejection, while most importantly achieving at least an order of magnitude better audio response over the signal bandwidth. Moreover, in the manufacturing process, complicated alignment is eliminated which decreases the alignment time from as much as two hours to typically under two minutes.

Claims

1. A superheterodyne subcarrier FM receiver operating in the 53-100 KHz SCA band for receiving music and voice transmission comprising:

means for detecting a signal having a carrier and an FM-modulated subcarrier, said subcarrier having a first predetermined frequency;

input filter means tuned to said subcarrier having a first predetermined frequency;

an oscillator providing a fixed frequency output signal having a second predetermined frequency, said oscillator including a ceramic resonator;

means for heterodyning said filtered subcarrier signal with said output signal so as to produce a resultant signal having a third predetermined frequency;

ceramic bandpass filter means having a bandwidth commensurate with said music and voice transmission, said filter means tuned to said third predetermined frequency and coupled to the output of said heterodyning means for producing a filtered output signal; and

,

FM demodulating means coupled to the output of said bandpass filter for demodulating said last-mentioned output signal to retrieve the audio components thereof such that the use of said ceramic resonator and said ceramic bandpass filter provides a receiver bandpass characteristic for low group delay, improved impulse noise rejection and improved high-end audio frequency response due to a resulting flat receiver bandpass response over the signal bandwidth.

2. An SCA FM receiver comprising:

means for heterodyning a received signal with a fixed frequency signal;

a local oscillator for generating said fixed frequency signal including a ceramic resonator controlled oscillator;

a ceramic bandpass filter coupled to said heterodyning means to provide the receiver with a passband commensurate with music and voice transmission and,

demodulation means coupled to said ceramic bandpass filter such that the use of said ceramic bandpass filter and said ceramic resonator in the receiving circuitry provides said receiver with a passband characteristic for improved sound quality, low group delay, improved impulse noise rejection and improved high-end audio frequency response due to a resulting flat receiver bandpass response over the signal bandwidth.

3. The receiver of claim 2 wherein said passband characteristic includes a flat passband response within the bandwidth of the SCA signal and rapid roll off of greater than 30 dB within 5 kHz.

4. The SCA receiver of claim 2 wherein the heterodyning circuitry includes no LC-tuned frequency-conversion or bandpass circuits.

5. An SCA FM receiver for receiving music and voice transmission and having a fixed frequency heterodyning circuit including frequency-conversion and bandpass filter circuits, said frequency conversion circuit having only a ceramic resonator as a frequency determining element and said bandpass filter circuit having only a ceramic resonator as a frequency determining element, with said ceramic resonators providing a bandpass characteristic for low group delay, improved impulse noise rejection and improved high-end audio frequency response due to a resulting flat receiver bandpass response over the signal bandwidth commensurate with SCA music and voice transmission.

6. The receiver of claim 5 wherein said bandpass filter circuit has a maximum ratio of bandwidth to center frequency of less than 4% due to the use of said ceramic resonators.

7. The SCA receiver of claim 6 wherein said receiver is substantially prealigned due to the use of said ceramic resonators.

8. A pretuned SCA FM receiver comprising:

a heterodyne circuit for receiving a signal and including a ceramic resonator controlled fixed frequency oscillator;

a ceramic bandpass filter coupled to the output of said heterodyne circuit and having a bandwidth commensurate with music and voice transmission; and

,

demodulation means coupled to the output of said bandpass filter, whereby said receiver is pretuned through the utilization of said ceramic bandpass filter and said ceramic resonator, with said ceramic bandpass filter and said ceramic resonator providing a receiver bandpass characteristic for low group delay, improved impulse noise rejection and improved high-end audio frequency response due to a resulting flat receiver bandpass response over the signal bandwidth.

9. A superheterodyne SCA FM receiver for receiving music and voice transmission comprising:

means for detecting a signal having a carrier and an FM-modulated subcarrier, said subcarrier having a first predetermined frequency;

a fixed frequency oscillator providing an output signal having a second predetermined frequency, said oscillator including a ceramic resonator;

means for heterodyning said detected subcarrier signal with said oscillator output signal so as to produce a resultant signal having a third predetermined frequency;

ceramic bandpass filter means tuned to said third predetermined frequency and coupled to the output of said heterodyning means for producing a filtered output signal; and

,

FM demodulating means coupled to said filtered output signal to retrieve the audio components thereof such that the use of said ceramic bandpass filter and said ceramic resonator provides a receiver bandpass characteristic for low group delay, improved impulse noise rejection and improved high-end audio frequency response due to a resulting flat receiver bandpass response over the signal bandwidth.