Modulation analyzer and level measurement device

A method is provided for determining a modulation of a CATV channel, the modulation being one of a digital modulation and an analog modulation. The method includes passing at least a portion of a tuner output from a tuner to a RF detector, and passing a RF detector output from the RF detector to a sync detector. The method further includes attenuating at least a portion of a sync detector output to create a remaining portion of the sync detector output, and passing the remaining portion of the sync detector output to a peak detector. The method further includes passing an output of the peak detector to a subsequent device, the output of the peak detector indicating whether the modulation of the CATV channel.

FIELD OF THE INVENTION

The present invention relates generally to level measurement and comparison devices for use in community antenna television (“CATV”) systems, and in particular to level measurement and comparison devices for use in CATV systems including content being passed using an analog modulation and content being passed using a digital modulation.

BACKGROUND OF THE INVENTION

The use of a CATV system to provide internet, voice over internet protocol (“VOIP”) telephone, television, security, and music services is well known in the art. In providing these services, a downstream bandwidth (i.e., radio frequency (“RF”) signals, digital signals, and/or optical signals) is passed from a supplier of the services to a user, and an upstream bandwidth (i.e., radio frequency (“RF”) signals, digital signals, and/or optical signals) is passed from the user to the supplier. For much of the distance between the supplier and the user, the downstream bandwidth and the upstream bandwidth make up a total bandwidth that is passed via a signal transmission line, such as a coaxial cable. The downstream bandwidth is, for example, signals that are relatively higher in frequency within the total bandwidth of the CATV system while the upstream bandwidth is, for example, signals that are relatively lower in frequency.

Traditionally, the CATV system includes a head end facility, where the downstream bandwidth is initiated into a main CATV distribution system, which typically includes a plurality of trunk lines, each serving at least one local distribution network. In turn, the downstream bandwidth is passed to a relatively small number (e.g., approximately 100 to 500) of users associated with a particular local distribution network. Devices, such as high-pass filters, are positioned at various points within the CATV system to ensure the orderly flow of downstream bandwidth from the head end facility, through the trunk lines, through the local distribution networks, and ultimately to the users.

At various locations between the head end facility and the user, there are amplifiers and slope adjustment devices for the purpose of maintaining the quality of the downstream bandwidth. This statement introduces three terms (i.e., quality, amplifiers, and slope adjustment devices) that are important to the remaining discussion. These will be discussed broadly below.

The quality of the downstream bandwidth is often a measure of: (i) a signal level of a particular channel within the downstream bandwidth, the signal level referred to merely as “level;” and (ii) a general consistency of levels across all of the channels in the downstream bandwidth, the general consistency referred to as “slope.” These objective measurements are often used by technicians to evaluate CATV system performance during operation and to troubleshoot customer complaints.

The level of each channel should fall within a specific range that has been determined to provide satisfactory video, sound and information transfer rates for users. The specific requirements for each channel are not of importance to the present discussion, but it is helpful to understand that there are specific targets for the level of each channel. Note that this is a simplistic definition to explain “level,” and note that this definition does not include other variances such as between analog and digital.

Slope is a measurement used to assess the amount of loss experienced due in large part to cable length. While all channels experience some loss, channels transmitted using higher frequencies within the downstream bandwidth experience more loss than those transmitted using lower frequencies. Accordingly, when the levels for all of the channels within the downstream bandwidth are graphed such that they are arranged in order according to the frequency of the channel, there may be a significant visual downward slope in the graph from the lowest frequency channel to highest frequency channel. This downward slope becomes more prominent as the length of signal cable increases. Note that this is a simplistic definition to explain the consistency of levels across all of the channels and the “slope” that is created by losses occurring in the signal cables. Also note that this definition does not include other variances such as between analog and digital.

For at least the forgoing reasons, a need is apparent for a device, which can accurately measure the level of channels present in the downstream bandwidth and accurately compare these measurements to determine whether amplification is required and whether slope adjustment is required.

SUMMARY OF THE INVENTION

The present invention helps to increase the quality of the downstream bandwidth. Increasing the quality of the downstream bandwidth improves customer satisfaction and reduces expenditures relating to customer complaints.

In accordance with one embodiment of the present invention, a modulation analyzer and level measurement device is provided for use with a CATV system. The device includes, a tuner, a band pass filter connected electrically downstream the tuner, and an RF detector connected electrically downstream the band pass filter. The device further includes a sync detector connected electrically downstream the RF detector, and a peak detector connected electrically downstream the sync detector.

In accordance with one embodiment of the present invention, a method is provided for determining a modulation of a CATV channel. The modulation being one of a digital modulation and an analog modulation. The method includes passing at least a portion of a tuner output from a tuner to a RF detector, and passing a RF detector output from the RF detector to a sync detector. The method further includes attenuating at least a portion of a sync detector output to create a remaining portion of the sync detector output, and passing the remaining portion of the sync detector output to a peak detector. The method further includes passing an output of the peak detector to a subsequent device, the output of the peak detector indicating whether the modulation of the CATV channel.

DETAILED DESCRIPTION

Referring toFIG. 1, a measurement device100may include an RF connector110, which may be any of the connectors used in the art for connecting a signal cable to a device. For example, the RF connector110may be a traditional “F-type” connector.

The term “connected” is used throughout to mean optically or electrically positioned such that current, voltages, and/or light are passed between the connected components. It should be understood that the term “connected” does not exclude the possibility of intervening components or devices between the connected components. For example, the tuner130is connected to the RF connector110even though a fixed signal level adjustment device140is shown to be positioned in an intervening relation between the tuner130and the RF connector110.

The fixed signal level adjustment device140may be positioned between the RF connector110and the tuner130. The fixed signal level adjustment device140may be used to prevent the RF connector110from drawing too much power from a connected source. Further, the fixed signal level adjustment device110may be sized to provide the tuner130with the coupled downstream bandwidth having an appropriate amount of power for the tuner130and subsequent devices. Accordingly, one skilled in the art would understand, based on the present disclosure, whether the fixed signal level adjustment device140is required and what size of the fixed signal level adjustment device140is required for any particular RF connector110and tuner130combinations.

The tuner130is a traditional tuner device that can be “tuned” to selected channels based on an input from a microprocessor120. In particular the tuner130used in the present embodiment is provided with a target index number (Index #) that corresponds with CATV channels, as shown below in Table 1. The purpose for pointing out these index numbers is to show that CATV channels have not been introduced in an orderly fashion. For example, CATV channel 95 (Index # 5) is lower in frequency than CATV channel 14 (Index #10). Accordingly, the present microprocessor120controls the tuner130based on an index number that increments in ascending order along with the frequencies that the index number represents. If a more powerful microprocessor and/or a more complex software control are used, the index of channels, shown below, may not be necessary.

The term “microprocessor” used throughout should be understood to include all active circuits capable of performing the functions discussed herein. For example, the microprocessor120may be replaced with a microcontroller, a system specific digital controller, or a complex analog circuit.

The output voltage stream from the tuner130is typical of tuners in that the voltage stream is a single channel output spectrum voltage stream, which in the case of NTSC is 6 MHz. If the output voltage stream from the tuner415is an analog modulation, the spectrum will likely appear as shown inFIG. 2, which will be described in further detail below. If the output voltage stream from the tuner415is a digital modulation, the modulation will likely appear as shown inFIG. 3.

ReferringFIG. 2, an analog modulation spectrum270includes, in relevant part, a sound subcarrier272(“SOX272”), a color subcarrier274(“CLX274”), and a picture subcarrier276(“PIX276”). Note that other parts or subcarriers may be present or may be missing from the single channel output spectrum voltage stream, as various signal formats are different in accordance with differing standards. As is shown inFIG. 2, a total integrated power in the analog modulation spectrum270is not evenly distributed. Rather, the PIX276represents approximately 50% of the total power in the analog modulation spectrum270. Further, the integrated power between the PIX276and the CLX274varies with the content of any picture being output from the tuner130. However, a vertical synchronization portion278(“vertical sync278”) and a horizontal synchronization portion280(“horizontal sync280”) of the analog modulation spectrum270are located very near the PIX276and remain at a nearly constant power level. The SOX272, typically transmitted at −15 dBc (decibels below carrier) also remains at a nearly constant power level because it is frequency modulated. The lowest powered subcarrier is the CLX274, typically transmitted at −20 dBc, also remains at a nearly constant power level because it is phase modulated. Based on these ratios, the CLX274represents approximately 1% of the total power, and the SOX represents approximately 4.5% of the total power.

Referring now toFIG. 4, a digital modulation spectrum282has an evenly distributed integrated power transmitted at −10 dBc from an equivalent analog modulated carrier.

Referring back toFIG. 1, a relatively narrow band-pass filter150may be electrically connected to an output of the tuner130. The band-pass filter150removes extraneous signals above and below desired frequencies, which in the present embodiment is the PIX276(FIG. 2) provided by the tuner130. Alternatively, the band-pass filter150may be replaced by a narrow low-pass filter, as the vertical synchronization frequency is modulated low within the range of frequencies in accordance with NTSC. Similarly, the band-pass filter150may be replaced by a high-pass filter that removes extraneous signals below other desired frequencies provided by the tuner, such as the horizontal synchronization frequency. It should be understood that differing frequencies may need to be selected depending on the analog modulation scheme expected. A resulting frequency domain voltage stream is then passed to an RF detector160.

A resulting frequency domain voltage stream284(“analog voltage stream284”) (FIG. 4) is expected to pass from the band-pass filter150when the analog modulation spectrum270is provided by the tuner130, and a resulting frequency domain voltage stream286(“digital voltage stream286”) (FIG. 5) is expected to pass from the band-pass filter150when the digital modulation spectrum282is provided by the tuner130. While there is a significant power difference between the analog voltage stream284and the digital voltage stream286, this difference may not be sufficient to accurately discriminate between the analog voltage stream284and digital voltage stream286, especially because the incoming signal level of the individual channels may vary greatly. Accordingly, additional means, discussed more fully below, are provided to discriminate between the analog voltage stream284and digital voltage stream286.

The RF detector160converts the frequency domain voltage stream passed from the band-pass filter150into a time domain voltage stream (analog)292(FIG. 6) or (digital)294(FIG. 7). More specifically, the RF detector160performs the effect of an inverse Laplace, the Laplace transform being a widely used integral transform, to convert the portion of the downstream bandwidth from a frequency domain voltage stream into a time domain voltage stream. The inverse Laplace transform is a complex integral, which is known by various names, the Bromwich integral, the Fourier-Mellin integral, and Mellin's inverse formula. An alternative formula for the inverse Laplace transform is given by Post's inversion formula. Accordingly, any other device capable of such a conversion from the frequency domain to the time domain may be used in place of the RF detector160. Afterward, the time domain voltage stream292,294is passed to both a synchronization detector170(“sync detector170”) and a low frequency level detector180.

The time domain voltage stream292,294differs depending on whether the frequency domain voltage stream is the analog voltage stream284or the digital voltage stream286. For example,FIG. 6is a typical baseline time domain signal voltage stream (analog)292from the RF detector160when the analog voltage stream284is passed to the RF detector160. As shown inFIG. 6, a very large portion of the time domain voltage stream (analog) includes vertical synchronization pulses288and horizontal synchronization pulses290. Accordingly, the time domain voltage stream (analog)292relative to the analog voltage stream284includes distinct and large components that have specific time periods.

The voltage stream represented inFIG. 7is the typical baseline time domain voltage stream (digital)294from the RF detector160when the digital voltage stream286is passed to the RF detector160. As shown inFIG. 7, the time domain voltage stream (digital)294includes none of the distinctive attributes present in the time domain voltage stream (analog)292, such as components having specific time period and specific amplitude relationships.

The sync detector170attempts to extract timing information from the time domain voltage stream292,294. For example, with the time domain voltage stream (analog)292(generated from the analog voltage stream284) the sync detector170extracts the vertical sync278and the horizontal sync280, and the sync detector170provides a sync detector voltage stream (analog)296represented inFIG. 8. In the present embodiment, the sync detector voltage stream (analog)296has a period of 16.8 milliseconds and a duty cycle of 1.37%. Further, the sync detector output296results in a fundamental frequency of 59.5 Hz with harmonics starting above 4300 Hz, which means that a significant amount of energy resides in the fundamental frequency of 59.5 Hz. These values are optimal, but other values are possible.

In contrast to the sync detector voltage stream (analog)296, a sync detector voltage stream (digital) from the sync detector170is either high or low and randomly flips back and forth at a rate of less than 5 seconds, in the present embodiment, when the digital voltage stream286is passed into the sync detector170. More specifically, the energy present in the sync detector voltage stream (digital) resulting from the digital voltage stream286is randomly distributed among the frequencies that are well below 0.2 Hz. Accordingly, the sync detector170generates a significant amount of time domain separation between the sync detector voltage stream (analog)296and the sync detector voltage stream (digital) in the output of the sync detector170.

The sync detector output (either analog or digital) is then passed to a low-pass filter190. The low-pass filter190is provided having a low frequency zero caused by an input blocking capacitor. This arrangement removes frequencies well below 59.5 Hz and frequencies above 300 Hz leaving only the fundamental vertical sync frequencies. Accordingly, when the sync detector170provides the sync detector voltage stream (digital), the low-pass filter190passes essentially no energy to a peak detector195connected electrically downstream the sync detector170. These values are optimal, but other values are possible.

The peak detector195produces a relatively consistent voltage stream when the sync detector170and the low-pass filter190provide a voltage stream including synchronous voltages. In the presence of a voltage stream including random, non-synchronous voltages, which is the case in the presence of the sync detector voltage stream (digital), the peak detector195is unable to produce a voltage steam that is consistently a significant voltage above ground. Accordingly, the peak detector195remains in a low logic state in the presence of the sync detector voltage stream (digital). Alternatively, when portions of the sync detector voltage stream (analog)296are passed from the low-pass filter190, the peak detector195sees significant amounts of energy, and the peak detector195changes to a high logic state. The peak detector195may also be referred to as a level detector and/or an integrator performing a similar function.

A resulting voltage stream from the peak detector195is input along a path200into the microprocessor120as a signal that discriminates between analog modulation channels and digital modulation channels. More specifically, the voltage stream from the peak detector195indicates that the tuner130is tuned to an analog modulation channel when the voltage stream is consistently a significant voltage above ground. Conversely, the voltage stream from the peak detector195indicates that the tuner130is tuned to a digital modulation channel when the voltage steam is consistently near ground. Alternatively, the peak detector195may be an inverting peak detector. When such an inverting peak detector is used, the voltage stream would be a significant voltage below the power supply rail when the tuner130is tuned to an analog modulation channel.

As mentioned above, the voltage stream from the RF detector160is also passed to the low frequency level detector180and an integration capacitor (not shown) connected electrically between the low frequency level detector180and a DC shift amplifier185. The low frequency level detector180and integration capacitor are used to integrate the total power of the voltage stream coming out of the RF detector160. For example, a digital modulation is −10 dBc in relation to the analog PIX276, the power in the two types of modulations (analog and digital) is equal. Accordingly, the detected voltage at the integration capacitor is similar between the two types of modulations (i.e., analog and digital). The voltage stream from the low frequency level detector180and integration capacitor is then input into the DC shift amplifier185. The low frequency level detector180may also be known as a peak detector.

The DC shift amplifier185may be used as a low pass amplifier to provide a voltage stream that has been shifted in scale by a known amount to render the signal voltages appropriate for the microprocessor120. The amount of voltage shift and/or amplification is determined by a voltage source155connected to the DC shift amplifier185by an adjustable attenuator165. Accordingly, the DC shift amplifier185may also be known as a low-pass amplifier. A portion of the voltage stream from the DC shift amplifier185is passed back to an automatic gain control input of the tuner130that adjusts a total system gain. This voltage stream holds the tuner output at a constant level. Additionally, a portion of the voltage stream from the DC shift amplifier185is passed to a high-gain amplifier175, and a portion of the voltage stream from the DC shift amplifier185is passed to a low-gain amplifier205.

The high-gain amplifier175is provided with the voltage stream from the DC shift amplifier185to function as a voltage comparator. For example, if any DC voltage shift is sensed at the output of the integration capacitor, from a DC voltage representing no input signal to the tuner, the high-gain amplifier175saturates and stays at a low side voltage power supply rail. Accordingly, this arrangement effectively makes a digital output that is high when there is no signal or channel, and low when there is any signal or channel. This arrangement provides a voltage stream in a path210to the microprocessor120to identify the occurrence of a transmitted channel present at the Index # tuned by the tuner130. Alternatively, the high-gain amplifier175may be inverting high-gain amplifier. When an inverting high-gain amplifier is used, the voltage stream would low when there is no signal or channel, and high when there is any signal or channel.

The low-gain amplifier205is also provided with the voltage stream from the DC shift amplifier185. The low-gain amplifier205is shifted in response to the voltage source215, which is connected to the low-gain amplifier205via an adjustable attenuator220. The gain of low-gain amplifier205is only large enough to cause the low-gain amplifier205to reach a positive voltage rail when an input voltage stream is at a high end of the allowable range of the input voltage stream. The resulting voltage stream from the low-gain amplifier205is relative to the level of the channel at the tuned index and is sufficient for the provision of the relative level to the microprocessor310. Further, the low-gain amplifier205scales the level of the channel at the tuned index for maximum resolution with respect to the microprocessor120. The voltage source215is used to calibrate a range of the low-gain amplifier205through adjustment of the adjustable attenuator220. Accordingly, the voltage stream provided in a path225to the microprocessor120is used to identify the level of a transmitted channel present at the Index # tuned by the tuner120.

The measurement device100may first be calibrated to provide a more accurate output to a laptop computer230or other output device. The calibration is accomplished by attaching the measurement device100to a matrix generator, which provides the measurement device100with at least two known levels, such as 0 dBmV and 20 dBmV, at every index number. The calibration sequence proceeds with the tuner130incrementing through each index number (from the chart provided above) and obtaining a calibration level for each index number. In the present embodiment, this calibration level is saved as a digital value between 0 and 255. The following is a chart of sample calibration levels, the values being chosen for exemplary purposes only:

Even though two calibration values are shown below for each channel, it is possible to use only one calibration value for each, with at least one assumption. For example, one calibration value only may be used if/when an assumed increment is used for voltage changes.

After the measurement device100is calibrated for use, the measurement device100may be attached at any location within a CATV system. The use and control of the measurement device may take a variety of different forms, a few of which will be outlined below.

One such use includes a technician entering a particular Index # or other channel identifier into the laptop computer230(or any other handheld or larger device). The measurement device100then provides channel information to the technician. This channel information may include: (i) whether a channel is present; (ii) whether the channel is being received in an analog or digital modulation, and (iii) the level of the channel being received. The technician may choose to review the provided information on a display screen and then act upon the information to attach and/or adjust signal conditioning equipment. The provided information may also be saved to a computer readable medium for review, data analysis and action such as the issuance of control system operational instructions based on the information, at a later date or on a more system wide basis.

Another such use includes a technician running a routine that samples channels at predetermined positions across the CATV transmission spectrum. In this example, the measurement device100may provide channel information relating to groups of channels for the purpose of making comparisons between the channels. As with above, this channel information may include: (i) whether the selected channels are present; (ii) whether the selected channels are being received in an analog or digital modulation, and (iii) the level of each channel being received. The technician may choose to review the provided information on a display screen and then act upon the information to attach and/or adjust signal conditioning equipment. The provided information may also be saved to a computer readable medium for review, data analysis and action such as the issuance of control system operational instructions based on the information, at a later date or on a more system wide basis.

Another such use includes incorporating the measurement device into a downstream bandwidth conditioning device that is used to condition the downstream bandwidth in terms of level and slope. Within such a device, the microprocessor120may increment the tuner130through at least two channels to determine an appropriate amount of level and slope adjustment to apply as part of the conditioning process.

While not explicitly shown inFIG. 1, the measurement device100may be remotely mounted from the laptop computer230(or any other handheld or larger device), such that the information provided to and from the microprocessor120is transmitted by any one of the know information transmission technologies, including, but certainly not limited to, DOCSIS, TCP/IP, RS232, and 802.11. Along these lines, it is envisaged that a plurality of measurement devices100may by placed at various locations around a CATV systems while being accessed by a single laptop computer230or other remote storage device, enabling individual user, group and broader system-wide analysis of operational parameters. It is envisaged that such analysis may lead to observation and the postulation of control instructions to optimize system operation for an individual user or group of cable subscribers.

While the present invention has been particularly shown and described with reference to certain exemplary embodiments, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by claims that can be supported by the written description and drawings. Further, where exemplary embodiments are described with reference to a certain number of elements it will be understood that the exemplary embodiments can be practiced utilizing either less than or more than the certain number of elements.