GB2503706A

GB2503706A - A self-terminating cable network splitter

Info

Publication number: GB2503706A
Application number: GB1211943.4A
Authority: GB
Inventors: Gerrit Boskaljon
Original assignee: Technetix BV
Current assignee: Technetix BV
Priority date: 2012-07-05
Filing date: 2012-07-05
Publication date: 2014-01-08
Also published as: GB201211943D0

Abstract

Each output port 24 of a device 20, such as a signal splitter, in a cable network is terminated locally by a 75 Ohm impedance in switch circuit 26 when the detection circuit 28 senses that downstream equipment has been disconnected from the port. The detector 28 may sense voltage or current. Radiation or ingress of RF signals at open ports is avoided, and ripple in the transfer characteristic of splitters and directional couplers is avoided.

Description

Title: Termination of Radio Frequency Connection Sites

Field of the invention

This invention relates to termination of radio frequency (RF) connection sites, such as RFports.

Background to the invention

In broadband cable networks, all RE connections between equipment, devices and other parts are made with coaxial connectors. To guarantee maximum energy a transfer, all RE ports must have the same characteristic impedance. When RE ports or other RF connection points are not used, they should be terminated with a characteristic impedance to ensure that stray RE signals are not pickcd up by thc port nor RF signals emitted by the port.

Summary of the invention

Tn accordance with one aspect of the present invention, there is provided a cable network device comprising one or more RE connection sites, for example RE ports, wherein each RE connection site is in communication with a switch means incorporating a termination, or resistive, element and each switch means is attached to a detection means or circuit, the switch means being operable in response to an output of the detection means so as to terminate the RE connection site when the detection means detects the port is unconnected to an external item.

In accordance with another aspect of thc present invention, there is provided a mcthod of terminating RE connection sites, for example RF ports, comprising: connecting a switch means incorporating a termination, or resistive, element to each RE connection site, connecting each switch means to a detection means and operating each switch means in response to an output from the detection means, thereby to ensure the RF connection site is terminated when the RE connection site is open and is unconnected to an extemal item.

I

Preferably the termination element has an impedance of 75 ohms as is generally required for cable networks. However, other characteristic impedances to match the impedance of a network incorporating the device may be used.

If required, a plurality of switch means may be attached to a common detection means, with the detection means controlling each switch means independently.

By providing automatic termination of an RE port as soon as the detection means detects the port is open and unconnected to any external or downstream item, the a device and method ensure that when items are disconnected from the RE port by a user, there is more or less instantaneous termination of the port and RE ingress or RE leakage cannot takc place.

Desirably the detection means is automatically operable to reverse the switch means on connection of an external item, so disconnecting the termination element as soon as an item is connected to the RF connection site.

The detection means may be responsive to detection of voltage or alternatively may be responsive to detection of current. Typically this will be done by way of a circuit that detects if there is a cunent or voltage. The outcome of the detection circuit is a vohage that will affect the state of the switch means and alter whether the RF connection site is terminated or not.

The termination clement may be integral with the switch means or may be provided as a separate element connected to the switch means. A preferred switch means with an integral termination element is an SPST Absorptive CATV UltraCMOS 75 ohm switch.

The invention will now be described, by way of example, and with reference to the accompanying drawings in which: Figure 1 is a schematic diagram showing an example RF device for explanatory purposes; and Figure 2 is a schematic diagram of a device in accordance with the present invention.

Description

RE devices 10 used in broadband cable networks and as shown in Figure 1 generally have a number of RE ports 12, 12' to which coaxial connectors can be attached, for example to establish a connection to an item of equipment owned by a subscriber. RF signals 14 are sent downstream from a network provider to device 10 and the signal fed through RF ports 12, 12' to a user device connected downstream of the port. If the RE port is unconnected to any user device and is left open, or un-terminated, as for port 12, it will act as an antenna picking up stray external RF signals and introducing these unwanted signals into the upstream signal path of the network. Similarly such a a non-terminated port receiving RE signals 14 from an upstream cable provider will radiate the RE signals. A simplified indication of the radiated or externally received RE' signal 16 is shown in Figure 1 by two-way signal 16. To avoid transmission or reception of RF signals by unconnected ports, ports are often terminated with a characteristic impedance or resistor 18 usually set to be 75 ohms, although the impedance value can be varied depending on the network requirements. The terminated port does not radiate RF signals nor does it receive unwanted RF signals.

In passive devices, like splitters and directional couplers, an open port causes a ripple in the transfer characteristics of the device. The more non-terminated ports the splitter or coupler has, the more ripple will arise so the effect becomes more extreme for increasing numbers of ports, such as for 3, 4, 6, 8, 12 way splitters.

Figure 2 shows a splitter 20 modified in accordance with the present invention, capable of receiving RF signals from a cable provider along input 22 and conveying RE signals downstream to user equipment or devices by way of ports 24. A two-way splitter is shown but splitters with 3, 4, 6, 8, 12 or more ports can be modified in a similar manner. Each output port 24 is associated with an automatic termination switch 26 connected in parallel to detection circuit 28. Switch 28 has an integral impedance, generally of 75 ohms. Detection circuit 28 is, in this instance, common to both ports, controlling the termination switch 26 for each port independently. If required a detection circuit can be provided for single or multiple ports. Detection circuit 28 detects if a port is connected to downstream equipment or a device and as long as the port is connected, circuit 28 leaves termination switch 26 in a non-terminated position and RE signals are free to pass downstream from splitter 20 to the port and thence to subscriber equipment, and conversely upstream signals are free to pass from subscriber equipment to splitter 20.

If external equipment is disconnected from any of the ports, detection circuit 28 detects this and activates termination switch 26 so terminating the disconnected port with thc impcdancc associatcd with thc switch. Detcction circuit 28 can bc rcsponsivc to either changes in voltage or current depending on the application.

a The detection circuit in combination with the termination switch ensures the RF ports terminate automatically when nothing is connected to the port, so preventing radiation of thc RE signal and cnsuring that no unwantcd RE signals arc pickcd up and introduced into the device or the network. The same principle of automatic termination can be applied to splifters with any number of ports, directional couplers and other RE devices with RF connection points.

Claims

Claims 1. A cable network device comprising one or more RF connection sites, wherein each RE connection site is in communication with a switch means incorporating a termination element and cach switch mcans is attachcd to a detcction means, thc switch mcans being opcrablc in response to an output of the detection means so as to terminate the RF connection site.
2. A cable network deyice according to claim 1, wherein the termination clement has an impedance of 75 ohms.
3. A cable network device according to claim I or claim 2, wherein a plurality of switch means are attached to a common detection means, with the detection means controlling each switch means independently.
4. A cable network device according to any of the preceding claims, wherein the detection means is automatically operable to reverse the switch means on connection of an external item to the RE connection site.
5. A cable network device according to any of the preceding claims, wherein the detection means is responsive to detection of voltage.
6. A cable network device according to any of claims Ito 4, wherein the detection means is responsive to detection of current.
7. A cable network device according to any of the prcceding claims, wherein thc termination element is intewal with the switch means.
8. A method ofterminating RF connection sites comprising: connecting a switch means incorporating a termination element to each RE connection site, connecting each switch means to a detection means and operating each switch means in response to an output from the detection means, thereby to ensure the RF connection site is terminated when the RF connection site is open and is unconnected to any external item.
9. A method of terminating RF connection sites according to c'aim 8, wherein the detection means detects automatically connection of an item to an RF connection site and operates the switch means to un-terminate the RF connection site.
10. A method of terminating RF connection sites according to claim 8 or claim 9, wherein io the detection means detects voltage to determine whether an RF connection site is unconnected.
11. A method of terminating RF connection sites according to claim 8 or claim 9, wherein the detection means detects current to determine whether an RE' connection site is unconnected.is
12. A cable network device and a method of terminating RE connection sites substantially as herein described with reference to and as illustrated by Figure 2.