CA1164965A - Wide band directional coupler - Google Patents

Wide band directional coupler

Info

Publication number
CA1164965A
CA1164965A CA000379487A CA379487A CA1164965A CA 1164965 A CA1164965 A CA 1164965A CA 000379487 A CA000379487 A CA 000379487A CA 379487 A CA379487 A CA 379487A CA 1164965 A CA1164965 A CA 1164965A
Authority
CA
Canada
Prior art keywords
transformer
coupler
output
winding
line
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000379487A
Other languages
French (fr)
Inventor
Prabhakara Reddy
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eagle Comtronics Inc
Original Assignee
Eagle Comtronics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eagle Comtronics Inc filed Critical Eagle Comtronics Inc
Priority to CA000379487A priority Critical patent/CA1164965A/en
Application granted granted Critical
Publication of CA1164965A publication Critical patent/CA1164965A/en
Expired legal-status Critical Current

Links

Abstract

ABSTRACT OF THE DISCLOSURE

A directional coupler to be inserted into a line for transmitting wide band signals. The line has a central conductor and a grounded outer conductor. The coupler has an input terminal and an output terminal to be electri-cally connected to the central conductor of the line. A
first series transformer has a primary winding and a secon-dary winding, with one side of the primary winding con-nected to the output terminal of the coupler. A second shunt transformer has a single winding connected between the other side of the primary winding and ground. The single winding has a first intermediate tap connected to the input terminal of the coupler and a second intermediate tap connected to an output tap point. The secondary winding of the first transformer is connected between the output tap point and ground. Sample signals applied to the output tap point by each transformer are in phase when the transformers are energized by wide band signals travelling along the line in a direction from the input terminal toward the output terminal of the coupler and are out of phase when energized by reflected signals travelling in the opposite direction. This invention increases the usable length of CATV transmission line without increasing the output level of the line amplifier. It provides a direc-tional coupler having a relatively low tap value coupled with improved input to output impedance matching; low insertion loss; good directivity and good frequency response.

Description

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describes a typical cable arrangement in which an amplifier is used to transmit a wide band signal over a speciEied length of cable. Seven directional couplers are situated at intervals of about 150 Eeet. As noted by Rheinfelder, insertion losses and line loss are experienced as the signal moves further away from the ampli~ier. As a result, the tap value of the couplers is reduced periodi-cally in order to maintain the signal level at the subscriber's set at a level required for good reception.
The nominal tap loss of the coupler becomes compressed the further the coupler is located from the amplifier.
Normally~ the tap value of the coupler is generally not allowed to drop below 12 dB because the reflection losses at these low values are typically high.
Some added disadvantages of conventional direc-tional taps having low values are poor frequency response, high insertion losses and reduced isolation.
The present invention seeks to increase the usable length of a CATV transmission line without increasing the output level of the line amplifier.
Accordingly the invention is a directional coupler that is adapted to be inserted into a line for transmitting wide band signals, said line having a central conductor and a grounded outer conductor, the coupler comprising an input terminal and an output terminal that are capable of being electrically connected to the central conductor o:E -the line, a first series transformer having a primary winding and a secondary winding, one side of said primary winding being connected to the ou-tput terminal of the coupler, a second shunt transformer having a single winding connected between the other side of said primary winding and ground, said single winding having a first intermediate tap connected to the input terminal of the coupler and a second intermediate tap connected to an out-put -tap point, said secondary winding of the first trans-former being connected between the output tap point and gxound so that sample signals applied to the output tap point by each transformer are in phase when the transEor-mers are energized by wide band signals travelling along the line in a direction from the input terminal toward the output terminal of the coupler and are out of phase when energized by reflected signals travelling in the opposite direction.
The invention provides a directional coupler having a shunt transformer for providing a voltage sample of a wide band television signal moving in a preselected direction along a coaxial transmission cable and a series transformer for providing a current sample of the wide band signal. The two sample signals are applied to a common output tap point from where it can be split and forwarded : 25 onto one or more subscriber terminals. The two transfor-mers are wound to provide the coupler with a relatively low , ,.

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nominal tap value whereby the coupler is suitable for use at an extended distance from the line amplifier. The win-dings of the shunt transformer are arranged to boost the internal impedance of the coupler at the input to the series transformer to a value that is greater than the charac-teristic line impedance thereby maximiæing the return loss and directivity of the device.
For a better understanding of the present inven-tion, reference is had to the following detailed descrip-tion of the invention which is to be read in conjunctionwith the accompanying drawings, wherein:
Figure 1 is a schematic diagram of a typical transmission line employing a directional coupler embodying the 3a , ,' '' '.. ' . ' :

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1lB4~ 5 particular arranyement the autotransfo:rmer, which was shown in the shunt position in Figure 2, is replaced by a more conventional transformer 40 having a primary section 41 and a secondary section 43. The primary section of the shunt transformer is provided with an intermediate tap 45 that is connected directly to the input terminal of the coupler. A
single turn 42 of the primary windings is positioned bet-ween the input terminal 21 of the coupler and the primary section 30 of the series transformer 26~ Here again the added internal impedance serves to minimize return losses thus permitting the device to operate at low tap values.
The secondary 43 of the shunt transformer is con-nected between ground and resistor 33 to develop the required voltage sample signal at the output -tap point 16.
The windings of the two -transformers are arranged so that the sample signals at the output tap point are additive when the broadcast signals are travelling along the cable in the direction of the arrow and cancel each other when reflected signals are moving back along the cable in the : 20 opposite direction.
The present invention provides a directional coupler having a relatively low tap value combined with improved input to output impedance matching charac-teristlcs, low insertion loss, and a good frequency response~
While this invention has been described with : '` ~``, reference to the disclosure set forth above, it is not necessarily limited to this par-ticular embodiment and this application is intended to cover any modifications or changes as may come within the scope of the presen-t inven-~ion.

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Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A directional coupler that is adapted to be inserted into a line for transmitting wide band signals, said line having a central conductor and a grounded outer conductor, the coupler comprising:
an input terminal and an output terminal that are capable of being electrically connected to the central con-ductor of the line, a first series transformer having a primary winding and a secondary winding, one side of said primary winding being connected to the output terminal of the coupler, a second shunt transformer having a single winding connected between the other side of said primary winding and ground, said single winding having a first intermediate tap connected to the input terminal of the coupler and a second intermediate tap connected to an out put tap point, said secondary winding of the first transformer being connected between the output tap point and ground so that sample signals applied to the output tap point by each transformer are in phase when the transformers are energized by wide band signals travelling along the line in a direction from the input terminal toward the output ter-minal of the coupler and are out of phase when energized by reflected signals travelling in the opposite direction.
2. The directional coupler of claim 1 wherein one turn of said single winding is placed between the input terminal of the coupler and the primary winding of the first transformer.
3. The directional coupler of claim 1 further comprising a resistor in series between the second inter-mediate tap and the output tap point of the coupler.
4. A directional coupler for insertion into a line for transmitting wide band signals that has a center conductor and a grounded outer conductor comprising:
an input terminal and an output terminal for con-necting the coupler in series with the center conductor of the transmission line, an output tap point, a shunt transformer and a series transformer each having a primary winding and a secondary winding, the primary winding of said shunt transformer being connected between ground and one side of the primary of said series transformer and the other side of the pri-mary of said series transformer being connected to the out-put terminal of the coupler, the secondary winding of the series transformer being connected to ground on one side and to said output tap point on the other side, an intermediate tap on the windings of the pri-mary winding of the shunt transformer that is connected to the input terminal of the coupler whereby a portion of said windings is positioned between the intermediate tap and the primary winding of the series transformer whereby the impe-dance at the input to the series transformer is greater than the characteristic impedance of the transmission line, and the secondary of said shunt transformer being connected to ground on one side and to said output tap point on the other side whereby a pair of in phase sample signals is applied to the output tap point when the trans-formers are energized by the wide band signals transmitted along the line in a direction from the input terminal of the coupler towards the output terminal.
5. The directional coupler of claim 4 wherein a single turn of the primary winding of said shunt trans-former is placed between the input terminal of the coupler and the input to the series transformer.
6. The directional coupler of claim 4 further comprising a resistor positioned between the output sides of the two secondary windings.
7. A directional coupler for insertion into a line for transmitting wide band signals that has a center conductor and a grounded outer conductor comprising:
an input terminal and an output terminal for con-necting said coupler in series with the center conductor of the transmission line, an output tap point, a first transformer having an input winding, an intermediate tap connected to said input terminal which divides said input winding into a first section of N1 turns and a second section of N2 turns, said second section being connected to said outer conductor, and an output means con-nected to said output tap point for supplying output signals corresponding to signals passing through said first transformer input winding to said output tap point, and a second transformer having an input winding con-nected in series between the first section of said first transformer input winding and said output terminal for raising the impedance at the input to said second trans-former to a level greater than the characteristics impe-dance of the transmission line, and an output means connected to said output tap point for supplying output signals corresponding to signals passing through said second transformer input winding to said output tap point.
8. The directional coupler of claim 7 wherein said first transformer is an autotransformer.
9. The directional coupler of claim 7 wherein said first transformer contains a primary and a secondary section.
10. The directional coupler of claim 7 wherein N1 is a single turn.
CA000379487A 1981-06-10 1981-06-10 Wide band directional coupler Expired CA1164965A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA000379487A CA1164965A (en) 1981-06-10 1981-06-10 Wide band directional coupler

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA000379487A CA1164965A (en) 1981-06-10 1981-06-10 Wide band directional coupler

Publications (1)

Publication Number Publication Date
CA1164965A true CA1164965A (en) 1984-04-03

Family

ID=4120200

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000379487A Expired CA1164965A (en) 1981-06-10 1981-06-10 Wide band directional coupler

Country Status (1)

Country Link
CA (1) CA1164965A (en)

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