Splitter for antenna for AM-FM, CB and method of conversion

• US 4,157,547 A
• Filed: 03/10/1977
• Issued: 06/05/1979
• Est. Priority Date: 03/10/1977
• Status: Expired due to Term

• Current Assignee: National Industries Incorporated
• Original Assignee: Tenna Corporation
• Inventors: Freimark, Ronald J., Isaacson, Robert E.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Masinick, Michael A.
• Application Number:
  US05/776,244
• Time in Patent Office: 817 Days
• Field of Search: 325/15, 325/20, 325/25, 325/381, 343/715, 343/745, 343/749, 343/750, 343/850, 343/858, 343/860, 343/180, 343/176
• US Class Current: 455/74
• CPC Class Codes: H03H 7/466 particularly adapted as input circuit for receivers

Abstract

An electrical circuit and method for providing electrical coupling from a CB antenna to both a CB (Citizen'"'"'s Band--Class D) transceiver and to an AM-FM receiver (amplitude modulation--frequency modulation) whereby only a single antenna need be used for both CB transceiver and AM-FM receiver.

Claims

1. In a system including a CB transceiver having a receiving CB input circuit and a transmitting CB output circuit for receiving an transmitting CB signals within a CB frequency range with the CB input and output circuits having a first impedance, and an AM/FM receiver having an AM input circuit having second input impedance for receiving AM signals within an AM frequency range and an FM input circuit having a third input impedance for receiving FM signals within an FM frequency range, the improvement comprising:

an antenna structure having an effective length approximately equal to 1/4 wavelength at approximately the center of the CB frequency range, and including a loading coil, said antenna structure being effective for receiving the FM signals over the FM frequency range, said antenna structure having an effective length for receiving the AM signals over the AM frequency range, splitter means for electrically connecting said antenna structure with the CB transceiver input and output circuits and the AM and FM input circuits and comprising splitter circuit means having a common splitter circuit for connectng all signals to and from said antenna structure and splitter AM/FM output circuit means for transmitting AM and FM signals to the AM and FM input circuits and substantially rejecting the CB signals and splitter CB circuit means for transmitting CB signals beween said antenna structure and the CB input and output circuits while substantially rejecting AM and FM signals, a first single connecting coaxial cable having one end electrically connected to said antenna structure and coil and an opposite end electrically connected to said common circuit, a second coaxial cable connected between said splitter AM/FM output circuit and the AM/FM input circuits, and a third coaxial cable connected between said splitter CB circuit and the CB input and output circuits, said first coaxial cable having a characteristic impedance providing an impedance match with the AM and FM input circuits and an impedance mismatch with the CB transceiver input and output circuits, said second coaxial cable having a characteristic impedance providing an impedance match with the AM/FM input circuits, and said third coaxial cable having a characteristic impedance providing an impedance match with the CB input and output circuits, said splitter CB circuit means comprising CB reactive circuit means having a reactance for blocking AM and FM signals and transmitting CB signals and having a preselected net reactance, said net reactance selected in conjunction with the characteristic impedance and length of said first coaxial cable, said antenna structure and said third coaxial cable to provide substantially an impedance match with the CB transceiver input and output circuits.

2. The system of claim 1 with said net reactance in conjunction with the characteristic impedance and length of said first coaxial cable, said antenna structure and said third coaxial cable providing a standing wave ratio proximate unity.

3. The system of claim 1 with said CB reactive circuit means comprising a non-resonant series L-C circuit with the magnitudes of L and C selected to provide a high impedance to the FM and AM signals, respectively, and with the magnitudes of L and C providing said net reactance.

4. The system of claim 1 with said antenna structure being predeterminedly non-resonant generally at the center of the CB range and with said net reactance compensating for such non-resonance to provide the impedance match with the CB transceiver input and output circuits.

5. The system of claim 1 with said splitter AM-FM output circuit means comprising AM-FM reactive circuit means having a reactance for blocking CB signals and transmitting AM-FM signals.

6. The system of claim 5 with said AM-FM reactive circuit means comprising a parallel resonant L-C circuit being resonant generally at the center of the CB range and providing a high impedance to CB signals.

7. The system of claim 6 with the desired magnitude of said net reactance selected to occur generally at the center of the CB frequency range.

8. The system of claim 6 with the AM-FM receiver having an AM portion and an FM portion and with the AM portion having a tuned circuit with a trimmer capacitor for peak tuning and with the improvement further comprising a padder capacitor serially connected with said L-C circuit for compensating for the capacitance of said antenna structure whereby the range of tuning of the trimmer capacitor is extended.

9. In a system including a CB transceiver having a receiving CB input circuit and a transmitting CB output circuit for receiving and transmitting CB signals within a CB frequency range with the CB input and output circuits having a first impedance, and an AM/FM receiver having an AM input circuit having a second input impedance for receiving AM signals within an AM frequency range and an FM input circuit having a third input impedance for receiving FM signals within an FM frequency range, an antenna structure including a loading coil and having an effective length approximately equal to one quarter wave length at approximately the center of the CB frequency range and having a length portion effective for receiving the FM signals over the FM frequency range, the antenna structure having an effective length for receiving the AM signals over the AM frequency range, splitter means for electrically connecting the antenna structure with the CB transceiver input and output circuits and the AM and FM input circuits and comprising splitter circuit means having a common circuit for connecting all signals to and from the antenna structure and a splitter AM/FM output circuit for transmitting AM and FM signals to the AM and FM input circuits and substantially rejecting CB signals and a splitter CB circuit for transmitting CB signals between the antenna structure and the CB input and output circuits while substantially rejecting AM and FM signals, a first common connecting coaxial cable having one end electrically connected to the antenna structure and loading coil and an opposite end connected to the common circuit, a second coaxial cable connected between the splitter AM/FM output circuit and the AM/FM input circuits, and a third coaxial cable connected between the splitter CB circuit and the CB input and output circuits, the method comprising:

providing a series L-C circuit in the splitter CB circuit and selecting the magnitudes of L and C to provide a high impedance to the FM and AM signals, respectively, and with the magnitudes of L and C providing a net reactance, determining the impedance of the antenna structure, and using the known characteristic impedance of the first common cable, selecting the height of the antenna structure, the length of the first common cable and the magnitude of the net reactance to provide an impedance match with the CB input and output circuits and a standing wave ratio approximately at unity.

10. In a system including a CB transceiver having a receiving CB input circuit and a transmitting CB output circuit for receiving and transmitting CB signals within a CB frequency range with the CB input and output circuits having a first impedance, and an AM-FM receiver having an AM input circuit having a second input impedance for receiving AM signals within an AM frequency range and an FM input circuit having a third input impedance for receiving FM signals within an FM frequency range, an antenna structure having a tip portion, a mast portion and a loading coil and having an effective length approximately equal to one quarter wave length at approximately the center of the CB frequency range, the mast portion having a length effective for receiving the FM signals over the FM frequency range, the antenna structure having an effective length for receiving the AM signals over the AM frequency range, splitter means for electrically connecting the antenna structure with the CB transceiver input and output circuits and the AM and FM input circuits and comprising splitter circuit means having a common circuit for connecting all signals to and from the antenna structure and a splitter AM-FM output circuit for transmitting AM and FM signals to the AM and FM input circuits and substantially rejecting CB signals and a splitter CB circuit for transmitting CB signals between the antenna structure and the CB input and output circuits while substantially rejecting AM and FM signals, a first common connecting coaxial cable having one end electrically connected to the antenna structure and an opposite end connected to the common circuit, a second coaxial cable connected between the splitter AM-FM output circuit and the AM-FM input circuits, and a third coaxial cable connected between the splitter CB circuit and the CB input and output circuits, the second comprising:

providing the first common cable to have an impedance substantially matching the AM and FM input impedances while mismatching the impedance of the CB input and output circuits, providing the second cable to have an impedance substantially matching the AM and FM input impedances, providing the third cable to have an impedance substantially matching the CB impedance of the CB input and output circuits, providing a series L-C circuit in the splitter CB circuit and selecting the magnitudes of L and C to provide a high impedance to the FM and AM signals, respectively, and with the magnitudes of L and C providing a net reactance generally at the center of the CB frequency range, determining the impedance of the antenna structure and the characteristic impedance of the first common cable, and selecting the height of the antenna structure, the length of the first common cable and the magnitude of the net reactance to provide substantially at the center of the CB frequency range an impedance match with the CB input and output circuits and a standing wave ratio approximately at unity.

11. The method of claim 10 further comprising selecting the mast portion to have a length in the range of 12 to 38 inches, and selecting the effective length of the common antenna structure to be out of resonance at the center of the CB frequency range.

12. In a system including a radio having a receiving input circuit and a transmitting output circuit for receiving and transmitting signals within a first frequency range with first input and output circuits having a first impedance, and a second radio having a second receiving input circuit having a second input impedance for receiving second signals within a second frequency range, the improvement comprising:

an antenna structure having an adjustable length and a loading coil for receiving signals at approximately the center of the first frequency range, said antenna structure being effective for receiving the second signals over the second frequency range, splitter means for electrically connecting said antenna structure with the first radio input and output circuits and the second input circuit and comprising first splitter circuit means having a common splitter circuit for connecting all signals to and from said antenna structure and second splitter circuit means for transmitting signals within the second frequency range between said antenna structure and the second receiving input circuit while substantially rejecting signals in the first frequency range, a first coaxial cable having one end electrically connected to said antenna structure and an opposite end electrically connected to said common splitter circuit, a second coaxial cable connected between said splitter circuit and the second receiving input circuit and a third coaxial cable connected between said splitter circuit and the first input and output circuits, said first coaxial cable having a characteristic impedance providing an impedance mismatch with the first input and output circuits, said splitter means further comprising reactive circuit means having a reactance for blocking the second signals and transmitting the first signals and having a preselected net reactance, said net reactance selected in conjunction with the characteristic impedance and length of said first coaxial cable, said antenna structure, and said third coaxial cable for providing substantially an impedance match with the first radio input and output circuits.

13. In an AM/FM receiver and CB transceiver combination:

an antenna designed for CB transceiving having a loading coil;

a first coaxial cable from the antenna, said first cable having an impedance designed for use with the AM/FM receiver;

a parallel LC circuit connected between said first cable and an AM/FM receiver, resonant for CB frequency and thus of a high impedance to CB frequencies and of a low impedance for AM/FM frequencies; and

a second coaxial cable connected to a CB transceiver and having an impedance designed for use with the CB transceiver;

a series LC circuit connected between said first cable and said second cable, said series LC circuit being nonresonant for CB frequencies and thus of low impedance to CB frequency signals and having an inductance that provides a high impedance to FM frequency signals and having a capacitance that provides a high impedance to AM frequency signals;

said series LC circuit having a net reactive component chosen to offset the impedance mismatch of the first cable with respect to the CB transceiver and of a magnitude that with the other circuit components matches the impedance of said second coaxial cable.