Combined handset and POTS filter

Details Combined handset and POTS filter Combined handset and POTS filter

1997-09-18

2001-10-09

Kuntz, Curtis (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Testing of subscriber loop or terminal

C379S027010, C379S093060

Reexamination Certificate

active

06301337

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to telephone handsets, and more particularly to an improved telephone handset for use in testing lines carrying both POTS and xDSL communications.
2. Discussion of the Related Art
In recent years telephone communication systems have expanded from traditional plain old telephone system (POTS) communications to include high-speed data communications as well. As is known, POTS communications includes not only the transmission of voice information, but also PSTN (public switched telephone network) modem information, control signals, and other information that is transmitted in the POTS bandwidth, which extends from approximately DC to approximately 3.4 kilohertz.
New, high-speed data communications provided over digital subscriber lines, such as Asymmetric Digital Subscriber Line (ADSL), Rate Adaptive Digital Subscriber Line (RADSL), etc. (more broadly denoted as xDSL) provide for high speed data transmissions, as is commonly used in communicating over the Internet. As is known, the bandwidth for xDSL transmissions is generally defined by a lower cutoff frequency of approximately 30 kilohertz, and a higher cutoff frequency which varies depending upon the particular technology. Since the POTS and xDSL signals are defined by isolated frequency bands, both signals may be transmitted over the same two-wire loop.
A POTS splitter is typically provided at each end of a transmission system communicating both POTS and xDSL information. As is known, a POTS splitter circuit consists of a high-pass filter and a low-pass filter, which are used to separate the two signals (the POTS signal from the xDSL signal). Normally, the high-pass filter is built into the xDSL transceiver, whereas the low-pass filter (commonly referred to as a POTS filter) normally provided as a separate unit. In operation, the POTS filter operates to filter the high frequency xDSL signals in order to protect the POTS (e.g., telephone) circuitry. At the same time the POTS filter provides filtering and protection for higher frequency noise signals that are often associated with a ring signal, or the switching circuitry of a central office.
It has been found, however, that troubleshooting line problems on local loops carrying both POTS and xDSL communications is frequently more difficult than troubleshooting a POTS only local loop. Years ago, the service provider (phone company) installed telephone lines from the central office, all the way to the telephone. Thus, the service provider was responsible for the integrity of the line all the way to the termination point (at the telephone). However, in recent years, it has become the custom for the service provider to run the local loop only to a junction box at the customer premises (whether the customer premises is a business, personal residence, etc.). Therefore, when performing testing on the local loop, the service provider is responsible only for insuring the integrity of the local loop between the central office and the junction box at the customer premises.
Typically, testing of a line is performed by a service technician using a testing handset to test the line. Alternatively, testing may be performed using more elaborate and specialized test equipment such as a transmission impairment measurement system (TIMS). The technician will plug the testing handset into a junction of the line to test the quality of the communications at that junction, and thus verifying the integrity of the line between the junction and the central office. Usually, the junction tested is the junction provided at the customer premises. In short, this form of testing is performed “by ear”, wherein the field technician evaluates the line quality by listening to the quality of the sound/signal at the testing handset.
It has been found that a problem in this manner of testing often arises when there are shared communications on the same local loop. For example, when the customer not only has POTS service, but also subscribes to an xDSL service, technicians testing the line quality often detect noise signals within the POTS frequency band, when testing the line at the junction box, which noise signals are not audibly present on POTS telephones inside the customer premises.
Accordingly, it is desired to provide an improved method or apparatus for testing local loops that overcomes the shortcomings and disadvantages noted above.
SUMMARY OF THE INVENTION
In researching the shortcomings of the manner of testing line quality and in the testing handsets used in the prior art, it was determined that many of the perceived line problems were actually the result of intermodulation products. Testing handsets, as with other common telephone handsets, include internal circuitry that generates intermodulation products when receiving high frequency signals; the intermodulation product being a signal having a frequency defined by the differential of two higher frequency, received signals. When xDSL communications are occurring at the same time the technician is testing the line, intermodulation products generated by the handset from the high-frequency xDSL transmissions often generate noise in the audible frequency band, which interferes with the proper evaluation of the line test conducted by the technician. Since POTS filters are disposed between the junction box and the POTS telephones at the customer premises (for those customer premises having a xDSL communication service), such intermodulation noise signals are not present at the POTS telephones.
When a field technician is dispatched to test a local loop at a customer premises, the technician does not necessarily know whether that customer premise includes a xDSL service. Even if the service technician is made aware that the customer premises includes an xDSL service, the technician will still not know whether a device within the customer premise is transmitting information within the xDSL frequency band at any given time.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to a telephone handset for testing the transmission quality of a local loop. In accordance with one aspect of the invention, the telephone handset includes a connector configured to connect to the local loop at, for example, a junction box. The invention also includes a low-pass filter circuit electrically interposed between the connector and operational circuitry of the telephone handset. In operation, the low-pass filter is designed to pass (substantially undisturbed) electrical signals within the POTS frequency band from the connector to the operational circuitry. In the same way, the low-pass filter is designed to substantially block the passage of electrical signals above the POTS frequency range. In this way, the low-pass filter blocks the introduction of high frequency signals, which may otherwise generate intermodulation products within the audible range, from reaching the operational circuitry of the testing handset.
In accordance with the preferred embodiment of the present invention, the low-pass filter circuit is defined by a cutoff frequency ranging from approximately 3.4 kilohertz to approximately 10 kilohertz. In addition, means are further included for bypassing the low-pass filter. Preferably, this “bypass” means includes a manually-operated switch, such as a double-pole, double throw switch. Such a switch allows the service technician to switch the low-pass filter into and out of the circuitry, when desired. Alternatively, the “bypass” means may be automatically implemented. In this regard, circuitry may be pr

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