WO1996037929A1

WO1996037929A1 - Switching coax jack with amplified monitor

Info

Publication number: WO1996037929A1
Application number: PCT/US1996/006611
Authority: WO
Inventors: Dominic J. Louwagie; Steven L. Carolus; John M. Field; Daniel J. Murphy; Jeffrey O. Brown; James D. Dewey
Original assignee: Adc Telecommunications, Inc.
Priority date: 1995-05-22
Filing date: 1996-05-09
Publication date: 1996-11-28
Also published as: AU5737796A

Abstract

A switching coax jack (100) includes a first central conductor (120) connected to a monitor conductor (123) across an amplification circuit (124). The jack further includes conductors (222, 224) for providing power from an external source of electrical power to the amplification circuit.

Description

SWITCHING COAX JACK WITH AMPLIFIED MONITOR

I. BACKGROUND QF THE INVENTION

1. Field of the Invention

This invention pertains to switching coax jacks having a monitor port. More particularly, this invention pertains to such a jack having an amplified monitor port.

2. Description of the prior Art

Switching coax jacks are well known. An example of such is shown in U.S. Patent No. 4,749,968 to Burroughs. Such jacks may be housed in modular housings such as shown in U. S. Patent No. 4,815,104 to Williams et al. Jacks, such as those shown in U.S. Patent No. 4,749,968, may be provided with a monitor port as shown in Figure 1 of that patent as item number 36. The monitor port is connected to a central conductor of a jack across a resistor such that only a portion of the signal along the output central conductor of the jack is directed to the monitor port. This permits a signal along the output conductor to be monitored without interrupting the signal. Alternatively, such jacks have a switching function such that placement of a plug within the port of the jack associated with the output conductor can open the normal through circuit of the jack permitting a signal to be drawn off the jack for testing or redirection. In certain industries, such as the video transmission industry, signals are directed from a source along a coaxial cable. For example, in the cable TV industry, video signals may be collected at a facility by satellite receivers. The signals will be transmitted across coax cables at a base band level. From time to time, it is desirable to monitor the signals in order to set power levels. In fact, industry and government regulations require that certain power levels be maintained in cable TV signals.

In order to test the power level of cable TV signals coming from a source, the signal must be routed to test equipment. Such equipment requires that the signal coming into the test equipment is at the same power level as the signal coming from the source equipment. A reduction in the power of the signal coming into the test equipment will result in unreliable testing of the signal by the test equipment.

Prior art switching coax jacks with monitors were not adequate for permitting access to the signal for testing purposes. For example, with a prior art switching coax jack, a signal could not be drawn off a monitor port and then tested at the test equipment since the signal at the monitor port is reduced in power relative to the signal coming into the jack. As a result, reliable testing off the monitor port was not possible. With switching coax jacks of the prior art, a plug could be inserted into the OUT port of the jack to divert the entire signal to the test equipment. However, such a system would require interrupting service to a customer. In present CATV installations, when it is desired to test the power level of a signal, the entire signal is commonly diverted to the test equipment. This results in interrupting the service to a customer. Accordingly, testing of power in CATV installations is typically done during off-peak hours (such as 2 a.m.) . This requires having testing technicians available on site outside of normal business hours for the purpose of testing signals. In addition to being disruptive to the scheduling of technicians, such requirements may also be expensive since they may require payment of premium wages to technicians to work during such off-peak hours. II. SUMMARY OF THE INVENTION A switching coax jack is disclosed having a jack module housing containing at least a first central conductor and a monitor conductor. The housing further contains a power conductor connected to an external source of electric power. The monitor circuit is connected to the first central conductor across a resistive load selected to draw only a portion of a main signal off of the central conductor without substantial reduction in a power level of the main signal on the first central conductor. The monitor circuit includes an amplifier for receiving the portion drawn off of the main signal and amplifying the portion to a desired output level. The amplifier is connected to the power conductor as a source of power.

III. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation of a CATV installation with test equipment for monitoring power of a signal with a prior art testing set-up;

Fig. 2 is a schematic of the CATV system of Fig. 1 with an alternative prior art testing set-up;

Fig. 3 is a schematic representation of the present invention incorporated into the system of Fig. 2;

Fig. 4 is a schematic representation of a prior art switching jack having resistive monitoring;

Fig. 5 is a schematic representation of a prior art switching jack having inductive monitoring; Fig. 6 is a schematic representation of a jack according to the present invention with amplified monitoring;

Fig. 7 is a front, right side and top perspective view of the jack of Fig. 6; Fig. 8 is a top plan view of the jack of Fig.

7 with a cover removed;

Fig. 9 is an exploded view of the jack of Fig. 7; and Fig. 10 is an electrical schematic view of an amplification circuit for use in the present invention.

IV. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the several drawing figures in which identical elements are numbered identically throughout, a description of the preferred embodiment of the present invention will now be provided.

With initial reference to Fig. 1, a prior art CATV installation is shown which draws signals from a plurality of sources 10_lf10₂ through 10_n (such as satellite receivers or the like) . The signals from the sources 10-_L-IO- are sent along individual coaxial cables 11-_L-ll- to individual test equipment 12-_L-12-. The signal from the test equipment is then sent along coaxial cables ISi-lS-i to further equipment for distribution to CATV subscribers.

With the installation as shown in Fig. 1, the test equipment 12₁-12_n can continuously monitor the power of the signals on the cables 11_J.-11- to ensure that the power of the CATV signal is at a desired or minimum level. This monitoring is done without interruption of service to any customer. However, the test equipment 12_x- 12_n is very expensive. Commonly, such equipment may cost $28,000 per test equipment.

Since a typical CATV installation may have as many as 200 to 300 channels, providing a separate piece of test equipment such as equipment 12_X-12- for each line or channel would be prohibitively expensive. Therefore, CATV installations do not provide continuous monitoring of power levels as would be available in the schematic of Fig. 1. Instead, when it is desired to monitor a signal, the signal is routed away from the subscriber and to a single piece of test equipment. Fig. 2 shows an alternative prior art test system. In Fig. 2, the individual test equipments 12_x- 12_n of Fig. 1 have been replaced with individual switching jacks 12'₁-12'_n such as jacks 20 in the aforementioned U.S. Patent No. 4,747,968 to Burroughs, incorporated herein by reference. With reference to the specifications and drawings (including reference numerals) of U.S. Patent No. 4,749,968, cables 11-_L-II- may be connected to a rear connector of the jacks 12 '-_- 12 '_n for connection to so-called "OUT" conductors (shown and numbered as item 149 in Fig. 2 of the '968 patent) .

Similarly, cables 13_3.-13-, may be connected to a rear connector of jacks 12'₁-12'_n for connection to so-called "IN" conductors (shown and numbered as item 157 in Fig. 2 of the '968 patent) . In the absence of a jack plug inserted into port 50 (shown in Fig. 2 of the present application and similarly shown and numbered in Fig. 2 of the '968 patent) , the signal on cables 11-_L-II- flow unimpeded through jacks 12'₁-12'_n to cables 13_J.-13...

When it is desired to test a power level on one of cables 11-_.-11- (e.g. to test a power level on cable 11₂) , a patch cord 13" (having one end connected to test equipment 15 and a second end terminated at a jack plug not shown) is provided with its jack plug inserted within port 50. Port 50 is associated with a switching circuit (not shown in the present application but shown and discussed as element 156 in U.S. Patent No. 4,749,968) . Upon insertion of the jack plug into port 50, normal connection of cables 11₂ and 13₂ through jack 12 '₂ is broken and cable 13₂ is connected to electrical ground. Simultaneously, the switch circuit redirects signal flow from cable 11₂ to patch cord 13" and test equipment 15. When it is desired to test power on a different one of cables 11-_.-11- (e.g.. cable ll- , the jack plug of patch cord 13" is removed from port 50 of jack 12'₂ and inserted into port 50 of jack 12'-_. This action reestablishes electrical connection between cables 11₂ and 13₂ but breaks electrical connection between cables ll_: and 13-_..

The system of Fig. 2 permits testing of signals on any one of lines 11-_.-11- using only one test equipment 15. However, in testing any cable, the cable must be taken off-line with resulting interruption to a customer.

In order to avoid dissatisfied customers, the disruption of the service occurs during off-peak hours such as early morning hours when subscribers are typically not using their CATV service. While testing on selected equipment during off-peak hours does not result in substantially dissatisfied customers, it does require technicians and the like to be available at the installation during such abnormal hours. Such scheduling of employee hours is both an inconvenience and expensive. Also, it is desirable to avoid any disruption of customer service. In Fig. 2, jacks 12'₁-12'_n are shown with monitor ports 36 corresponding to port 36 in Fig. 12 of U.S. Patent No. 4,749,968. Insertion of a plug in port 36 permits connection to an OUT conductor associated with port 50. The connection is across a resistor to permit monitoring of the signal on cables lln-ll-, without interruption of signal flow to cables 13-_L-13_J..

However, for reasons that will be described, resistive monitoring jacks such as jacks 12^-12'_n (identical to those shown in U.S. Patent No. 4,749,968) are not suitable for testing cables 11-.-11- in CATV applications.

Fig. 3 illustrates a desired testing installation where the test equipment 12₁-12_n of Fig. 1 and modules 12'₁-12'_n of Fig. 2 are replaced by low cost jack modules lOO -100-. A single piece of test equipment 15 (as in Fig. 2) is provided to test the power on each of the coaxial cables ll-_^-ll-.

When it is desired to route from the modules 100-_L-lOO_u to the test equipment 15, a patch cord 13" or the like may be connected to test equipment 15 and individually attached to each of the modules

However, unlike the system of Fig. 2, the patch cord 13" is not connected to a switched port (i.e. , such as port 50 in Fig. 2) but to a monitoring port (such as port 36 in Fig. 2) .

Previously, it was indicated that connection of equipment 15 to the monitor ports 36 of jacks 12₁-12_n in Fig. 2 was undesirable. However, with a novel jack construction, applicants can connect a single test equipment 15 to a monitor port of a jack 100. This has the advantage of permitting testing of signals on cables ll -11- without breaking connection of the signals to cables 13_J.-13.,.

Before proceeding to a detailed discussion of the novel features of jack 100, a more thorough discussion of prior art jacks (such as jacks 12'₁-12'_n) will be provided to assist in an understanding of the present invention.

The prior art includes jacks for coaxial cables which permit monitoring of the signal without interrupting the signal. However, such jacks typically provide a substantial reduction in power by reason of the monitoring. For example, current telecommunications jacks which have a monitoring function commonly produce a -20 dB power loss across a resistor to the monitor port of the jack. Jacks 12'₁-12'_n (i.e. _r a jack shown in U.S. Patent No. 4,749,968) are examples of such a jack. Such a power loss is unacceptable since such a reduced power signal cannot be reliably placed in the test equipment 15 for purposes of. testing a CATV signal.

Fig. 4 illustrates in schematic form a prior art switching coax jack 12' such as jacks 12'₁-12'_n (i.e.. the jack and monitor of U.S. Patent No.

4,749,968) . In Fig. 4 the jack 12' is shown with a front monitor 36 and a rear monitor 36a. U.S. Patent No. 4,749,986 does not show a rear monitor but such are common. Jack 12' includes a first (or OUT) central conductor 20' and a second (or IN) central conductor 21' connected by a switching circuit 22' . Signal flow passes from conductor 20' to conductor 21' through switching circuit 22' . Attachment of a plug to either of conductors 20',21' results in activating the switching circuit 22' and breaking the electrical connection between conductors 20' and 21'. Monitor conductors 23',23a' (associated with ports 36,36a) are connected to conductor 20' across resistors 24',24a'. The resistors 24',24a' (typically about 464 ohms each) permit a portion of the signal on conductor 20' to be passed to the monitor conductors 23',23a' which permits monitoring of the signal on conductor 20'. However, due to the resistive nature of the monitoring, there is a substantial power drop between monitor conductors 23',23a' and the main signal conductor 20'.

Fig. 5 illustrates a further example of a prior art schematic for monitoring coax jacks. In the jack 12" of Fig. 5, the OUT conductor 20" is connected to IN conductor 21" across a conventional switching circuit 22". Conductor 20" is provided with an inline inductor 24". Monitor conductors 23",23a" are also provided with an inductor 24a" which is inductively coupled to inductor 24". Unlike the resistive monitoring of Fig. 4, the jack 12" of Fig. 5 provides for inductive monitoring. Such a jack is disclosed in U.S. Patent No. 5,348,491. However, there is still a substantial power loss from conductor 20" to monitor conductors 23",23a" across the inductive coupling of inductors 24",24a" .

The present invention is for an amplified switching coax jack 100 schematically shown in Fig. 6. In the amplified jack 100, a first (or OUT) central conductor 120 is electrically connected to a second (or IN) central conductor 121 across a conventional switching circuit 122. A monitor central conductor 123 is electrically connected to central conductor 120 across an amplification circuit 124. Amplification circuit 124 is connected to a conductor 120 across a very high resistance resistor 125 so that the portion of signal drawn off conductor 120 does not significantly result in decreased power on conductor 120. A power conductor 127 is provided to power the amplification circuit 124 and is connected to an external source of electrical power.

Through selection of the amplification circuit 124, the power differential between conductors 123,120 may be selected to be any desired power differential. In the preferred example for use of the jack for testing CATV signals, it is desirable that there be a zero power differential between conductors 123,120. With reference to Figs. 7-9, the present invention is illustrated as a switching coax jack 100 having a housing and configuration similar to that shown as jack 10 in Fig. 3 of commonly assigned and copending U.S. Patent application Serial No. 08/252,067 (also shown in related International Application

PCT/US92/05880, International Publication No. WO93/20600 published October 14, 1993) and as jack 10 in U.S. Patent No. 5,413,494, both incorporated herein by reference. The jack 100 includes an electrically conductive diecast housing 200 having a cover 202 for enclosing the housing 200. Cover 202 is secured to housing 200 by screws 203. The housing 200 presents three forward ports including a monitor port 204, an OUT port 206 and an IN port 208. Clips 201 are provided to secure the housing 200 in a chassis (not shown) containing a plurality of jacks 100.

A dielectric support 210 is provided to be placed within the housing 200. The dielectric support 210 maintains various electrical components in proper alignment within the housing 200 but in spaced alignment relative to the housing 200 which is electrically grounded.

Carried on the support 210 are a monitor conductor 123, an OUT conductor 120 (shown schematically in Fig. 6 as conductor 120 and in Figs. 8 and 9 as consisting of front and rear segments 214a,214b joined by inductor 214c) and an IN conductor 121 (shown schematically in Fig. 6 as conductor 121 and in Figs. 8 and 9 as consisting of front and rear segments 216a,216b joined by inductor 216c) . The conductors 123,120 and 121 are aligned with the monitor, OUT and IN ports 204,206,208, respectively. Rear segments 214b,216b are disposed within connectors 218,220 exposed on the rear of the housing 200. Insulative supports 219,221 support conductors 214b,216b within connectors 218,220.

The support 210 also contains two conductors 222,224 exposed through the rear of the housing for electrical connection to an external source of power

(not shown) . The jack 100 further includes a switching circuit (shown schematically in Fig. 6 as 122) including normal springs 226,228 for having normal electrical contact with the OUT and IN conductors' forward segments 214a,216a and with the normal springs 226,228 electrically connected by an inductor 230. The inductor 230 and normal springs 226,228 are selected for the jack 100 to have a desired impedance as is taught in the aforementioned International Publication No. WO93/20600 and U.S. Patent No. 5,413,494.

Cams 232,234 are provided pivotally mounted within the housing 200 on a pivot pin 233 and aligned with ground springs 238,240. Ground springs 238,240 are connected across resistors 242,246 to the electrically grounded housing 200. Insertion of a plug into the OUT port 206 causes the cam 232 to act against the ground spring 238 to engage and push the normal spring 226 out of electrical connection with the OUT conductor 214a and into grounded contact with the spring 238. Similarly, insertion of a plug into the IN port 208 causes the cam 234 to rotate urging the spring 228 away from the IN conductor 216a. A ground clip 241 spans ports 204,206,208 to ground the external surface of a plug inserted within the ports. It will be appreciated that the structure thus described forms no part of this invention per se and is illustrated solely for the purposes of providing an understanding of the present invention. Jacks having conductors and switching circuits thus described are disclosed in the aforementioned commonly assigned International Publication No. WO93/20600. In that document, pins similar to conductors 222,224 (i.e. , pins 62,53 in Fig. 3 of International Publication No.

W093/20600) are shown to complete a tracing circuit when a jack plug is inserted in a monitor port. Similar pins are shown in Fig. 3 of U.S. Patent No. 5,413,494 as items 70,72. The present invention further includes an amplification circuit 124 on circuit board 246 supported by the support 210 and contained within the housing 200. A screw 243 passes through board 246 and is received in bore 245 of housing 200 to provide an electrical ground for the circuit on board 246. Alternatively (or in addition) , a ground clip 244 received within pocket 247 is provided to permit optional connection of a wire (not shown) from the printed circuit board 246 to the housing 200 to establish a ground path between the circuit board 246 and the housing 200.

The amplification circuit 124 is shown in electrical schematic in Fig. 10 and is connected to the OUT conductor 214a across a resistor 125. Further, the monitor conductor 212 is connected to the amplification circuit 124 as are the power conductors 222,224.

The resistor 125 is selected for a combined impedance of circuit 124 and resistor 125 to have an insubstantial draw of signal from the OUT conductor 214a so that power across the OUT conductor from connector 218 to the OUT port 206 is not substantially reduced by reason of the amplification circuit 124. By insubstantial, it is meant a power drop of less than -10 illi dB. In a preferred embodiment, the resistor 125 is selected to be 500 ohms. Power is supplied to the amplification circuit

124 via current flow paths 127a, 127b, and 127c. In the preferred embodiment, current flow path 127a (connected to conductor pin 222) provides +5 volts dc to an operational amplifier Ul through fuse FI, current flow path 127b (connected to conductor pin 224) provides -5 volts dc to the operational amplifier Ul through fuse F2, and current flow path 127c is grounded (i.e. , by connection to ground screw 243) . The incoming power on signal flow paths 127a and 127b is fused by the fuses FI and F2, preferably at 0.2 Amps. The signal flow path 127a is connected to ground through filtering capacitors C3 and C4 and signal flow path 127b is connected to ground through filtering capacitors Cl and C2. The capacitors Cl through C4 and the resistance of the fuses FI and F2 filter the power carried by signal flow paths 127a and 127b. In the preferred embodiment, capacitors Cl and C3 are 2.2μF, forming a low pass filter, and capacitors C2 and C4 are O.OlμF for high frequency decoupling. It will be apparent to those in the art that any type of power source can be used to provide power to the amplification circuit 124, such as, for example, wall outlets or a 48 volt battery power supply, provided a power converter converts the power to the appropriate +/- 5 volts.

The operational amplifier Ul is configured as a non-inverting gain stage, which is known in the art. In the preferred embodiment, the operational amplifier Ul is product number AD818, manufactured by Analog

Devices, Inc. located in Norwood, Massachusetts. The input signal drawn from the conductor 214a (on wire 125a in Fig. 8) through resistor 125 flows through a signal flow path 128 to a noninverting input 129 of the amplifier Ul. A pair of diodes Dl and D2 are connected between the power signal flow paths 127a and 127b and the input signal flow path 128. The diodes Dl and D2 protect the amplification circuit 124 from over voltage, which is understood in the art. An inverting input 130 of the amplifier Ul is connected to a feedback network 132. The feedback network 132 connects the inverting input 130 to ground through resistor R2 and to an amplifier output 131 of amplifier Ul through capacitor C5 and resistor Rl. At low frequencies, the configuration of the operational amplifier Ul and the resistors Rl and R2 results in a gain of 2 when the resistors Rl and R2 are equal in value. In the preferred embodiment the resistors Rl and R2 are 1000 ohms, but other resistive values could be effectively used. The gain may vary by a small amount depending upon the resistors. The capacitor C5 in the feedback network 132 is used to flatten the gain curve and increase stability, such that the circuit does not oscillate. Finally, the operational amplifier output 131 is connected to output signal flow path 133 (connected to monitor conductor 123) through resistors R3 and R4 connected in series. In the preferred embodiment, the resistors R3 and R4 provide 74.8 ohms output impedance to match a 75 ohm coax cable. The resistors R3 and R4 in series operate as a voltage divider, and thus the output gain of 2 from the operational amplifier Ul is divided by 2. Therefore, the desired result in the preferred embodiment, zero dB, is attained. The amplification and the bandwidth of the system can be modified by changing the resistive ratio of the values of the resistors Rl and R2 in the feedback network 132. Thus, other dB values can be attained. While the foregoing description of amplification circuit 124 describes a preferred embodiment, it will be appreciated that the design of such circuit 124 is within the skill of the art. Modifications to the design can be made to achieve a desired dB and, more specifically, a zero dB jack 100.

With the structure thus described, each of the jacks lOOi-100- in Fig. 3 may be a jack 100 such as that described above. The cables llx-ll- may be connected to connector 218 such that the signals from the cables 11-.- ll_n are passed on the OUT conductors 214a of the jacks

100_x-100_n. The cables lSi-13- are connected to connectors 220. Accordingly, with the absence of a plug in either of the OUT or IN ports 206,208, a signal flows through the jack 100 from coax cable ll-_^-ll- to coax cable lSi-13- without interruption and without reduction in power.

A minute portion of the signal on OUT conductor 214a is drawn off to the amplification circuit 124 of each jack. The amplification circuit 124 receives power from conductors 222,224. The amplification circuit 124, in the preferred embodiment, amplifies the drawn off portion to a power level equal to a signal power level on the OUT conductor. When it is desired to test the power level of the signal on any of conductors ll -11- (e.g. , conductor 11₂) , a plug end of a patch cord 13" may be placed within the monitor port of jack 100₂ and connected to the test equipment 15. The test equipment 15 is now being provided with the CATV signal at a power level identical to the power level on conductors 11₂,13₂. During the entire testing of the signal, there is no interruption of the signal being provided to the subscriber.

With the present invention, a single piece of test equipment 15 can provide power testing of the cable TV signals without the need to provide any service interruption to customers. Also, the testing can be done at any time and need not be limited to off-peak hours. Further, were it to be desired, the entire signal on cables lli-11- can be routed from cables 13₃.-13- by inserting plug ends of patch cords into the OUT ports 206 of jacks IOO_J^-IOO-. Also, a new signal source can be readily connected to cables 13-_L-13- by connecting the source via a patch cord to the IN ports 208 of jacks

The present invention has been described in a preferred embodiment where the amplification circuit is selected to have a 0 dB loss from the OUT connector to the monitor conductor. However, it will be appreciated for different applications it may be desirable to have a selected dB loss. It will be recognized that by changing the amplification circuit and its characteristic components, any desired dB loss can be provided. Further, the signal can be amplified to a power level greater than that on the OUT conductor. For example, in the embodiment of Fig. 3, the amplification circuit 124 is selected for the jack 100 to have a zero dB loss between the monitor conductor 212 and the OUT conductor's forward segment 214a. The selection of a zero dB is made with the assumption that there is an insignificant loss of power on patch cord 13' ' . This assumption is acceptable for short patch cords (i.e.. less than about 50 feet) . For longer patch cords (i.e. , greater than 50 feet) , the power loss over the patch cord is sufficient to impair the reliability of the testing on test equipment 15. However, with a known length patch cord 13' ' , the power loss is determinable and the amplification circuit may be modified to compensate for the loss. For example, for a coax cable patch cord 13'' having a length of about 100 feet, the amplification circuit 124 is selected to have a 10 dB gain between monitor conductor 212 and OUT forward segment 214a to compensate for a calculated 10 dB loss on patch cord 13' ' . Such a modification to the amplification circuit 124 is well within the skill of the art for a person having the benefits of the teachings of the present invention. Having described the present invention in a preferred embodiment, it will be recognized by those skilled in the art that the present invention may be subject to modifications and equivalents which will be apparent to one skilled in the art having the benefits of the teachings of the present invention. It is intended that the present invention shall not be limited to the specific embodiment disclosed but shall include modifications and equivalents.

Claims

WHAT IS CLAIMED IS:

1. A coax jack comprising: a jack module housing; at least a first central conductor disposed within said housing and having means for connection of opposite first and second ends of said first central conductor to external coax conductors with said first central conductor carrying a main signal having a power level between said opposite ends, said means including at least a first port formed through said housing for receiving a jack plug at said first end and said means further including a coax connector at said second end; a monitor conductor disposed within said housing with means for connection of said monitor conductor to an external coax conductor; a monitor circuit for connecting said monitor conductor to said first central conductor at a point intermediate said opposite ends; at least one power conductor contained within said housing with means for connection of said power conductor to an external source of electric power; said monitor circuit connected to said first central conductor across a resistive load selected to draw a portion of said main signal on said first central conductor to said monitor circuit without substantial reduction in said power level of said main signal on said first central conductor; said monitor circuit including amplifying means for receiving said portion of said main signal and amplifying said portion to an amplified signal and delivering said amplified signal to said monitor conductor, said amplifying means connected to said power conductor.

2. A jack according to claim 1 wherein said amplifying circuit is selected for said amplified signal to have a power substantially the same as said power of said main signal.

3. A coax jack according to claim 1 further comprising a second central conductor contained within said housing and having means at a first end thereof for connection to an external coax conductor; a switching circuit contained within said housing with switch means for establishing an electrical connection between said first and second central conductors in an absence of said plug within said port and for opening said electrical connection upon insertion of said plug within said port.

4. A coax jack according to claim 1 wherein said resistive load is selected for a voltage drop from said connector to said port is less than a predetermined tolerance of telecommunication test equipment.

5. A coax jack according to claim 2 wherein said amplifying circuit is selected for a voltage on said monitor conductor to equal a voltage on said first central conductor at said port.

6. A coax jack according to claim 2 wherein said amplifying circuit is selected for a power ratio between said monitor conductor and said first central conductor at said port is 0 dB.

7. A coax jack according to claim 1 comprising grounding means for providing a grounded coax shield for said first central conductor, said amplifying circuit connected to said grounding means across circuit components.