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Claims  |
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We claim:
1. An apparatus for receiving sweep testing signals and generating frequency response values therefrom, the sweep testing signals generated in accordance with a predefined sweep plan by
a remote sweep transmitter, the sweep transmitter coupled to a communication system to be tested, the apparatus including:
a) a test input for connecting to a terminal of the communication system to be tested, the test input comprising an RF input;
b) a controller operable to
effect communication of the sweep plan with the sweep transmitter prior to connection of the test input to the terminal,
generate a sweep control signal, the sweep control signal responsive to the sweep plan;
c) a receiver circuit operably coupled to the test input for receiving sweep testing signals therefrom, the receiver circuit having a control input connected to receive the sweep control signal from the controller, the receiver circuit operable
to tune to a plurality of frequencies responsive to the sweep control signal;
d) a measurement circuit coupled to the receiver circuit and operable to generate measurement signal values corresponding to the plurality of frequencies, said measurement signal values comprising said frequency response values.
2. The apparatus of claim 1 further comprising a communication input operable to effect communication of the sweep plan between the controller and the sweep transmitter.
3. The apparatus of claim 2 wherein the communication input comprises a digital serial communication input.
4. The apparatus of claim 1 further comprising a memory coupled to the controller, and wherein the controller is further operable to
obtain the sweep plan from the memory, and
effect communication of the sweep plan to the sweep transmitter.
5. The apparatus of claim 1 further comprising a memory coupled to the controller, and wherein the controller is further operable to
effect communication of the sweep plan from the sweep transmitter communication input, and
provide the sweep plan to the memory.
6. The apparatus of claim 1 further comprising a display, and wherein the controller is further operable to
receive the measurement signals from the measurement circuit,
generate indication signals representative of the measurement signals, and
provide the indication signals to the display.
7. The apparatus of claim 1 wherein the receiver circuit is further operable to
receive an RF sweep signal from the test input, the RF sweep signal corresponding to the sweep plan, and
generate an intermediate frequency signal comprising a plurality temporal segments, each segment corresponding to one of the plurality of frequencies, and and wherein the measurement circuit is further operable to generate a measurement signal
for each segment.
8. The apparatus of claim 7 further comprising an analog-to-digital (A/D) converter coupled between the receiver circuit and the measurement circuit, and wherein the measurement circuit includes a digital signal processing circuit.
9. The apparatus of claim 1 wherein the receiver circuit is operable to receive a synchronization signal, wherein the measurement circuit is operable to provide a measurement signal based on the synchronization signal to the controller, and
wherein the controller is operable to generate the sweep signal after a predetermined delay from receiving the measurement signal based on the synchronization signal.
10. The apparatus of claim 1 wherein the measurement circuit is further operable to identify the synchronization signal from the measurement signal based on the synchronization signal and wherein the synchronization signal comprises a
predetermined number of pulses modulated onto a carrier signal having one of the plurality of frequencies.
11. The apparatus of claim 1 further comprising a user input operably connected to the controller, the user input operable to receive input signals representative of a sweep plan, and wherein the sweep plan is based on the received input
signals.
12. The apparatus of claim 1 wherein the receiver circuit further comprises a variable attenuator operable connected between the test input and the measurement circuit.
13. The apparatus of claim 1 wherein the receiver circuit further comprises a variable attenuator operable connected between the test input and the measurement circuit.
14. An apparatus for transmitting sweep testing signals for reception by a corresponding sweep testing receiver, the apparatus comprising:
a) a test output for coupling to a communication system to be tested;
b) a controller operable to:
effect communication of a sweep plan with the sweep receiver prior to connection of the sweep receiver to the communication system to be tested
generate a sweep control signal, the sweep control signal responsive to the sweep plan;
c) an RF transmitter having a control input connected to receive the sweep control signal from the controller, the RF transmitter operable to generate a sweep test signal responsive to the sweep control signal, the sweep test signal comprising a
plurality of RF test signals, each of the plurality of RE test signals having a distinct carrier frequency.
15. The apparatus of claim 14 further comprising a communication input for effecting communication of the sweep signal with the sweep testing receiver.
16. The apparatus of claim 14 further comprising a memory coupled to the controller, and wherein the controller is further operable to
obtain the sweep plan from the memory, and
effect communication of the sweep plan to the sweep testing receiver.
17. The apparatus of claim 1 further comprising a memory coupled to the controller, and wherein the controller is further operable to
effect communication of the sweep plan from the sweep testing receiver, and
provide the sweep plan to the memory.
18. An apparatus for receiving sweep testing signals and generating frequency response values therefrom, the sweep testing signals generated in accordance with a predefined sweep plan by a remote sweep transmitter, the sweep transmitter coupled
to a communication system to be tested, the apparatus including:
a) a test input having a first connection arrangement for connecting to a test output of the sweep transmitter and having a second connection arrangement for connecting to a terminal of the communication system to be tested;
b) a controller operable to generate a sweep control signal the sweep control signal responsive to a sweep plan;
c) a receiver circuit having a control input connected to receive the sweep control signal from the controller, the receiver circuit operable to tune to a plurality of frequencies responsive to the sweep control signal;
d) a measurement circuit coupled to the receiver circuit and operable to generate measurement signals corresponding to the plurality of frequencies;
and wherein the controller is further operable to
receive a first set of measurement signals from the measurement circuit when said test input is connected in the first connection arrangement,
receive a second set of measurement signals from the measurement circuit when said test input is connected in the second connection arrangement,
and generate a frequency response based on the first set of measurement signals and the second set of measurement signals.
19. The apparatus of claim 18 wherein the test input comprises an RF input.
20. The apparatus of claim 18 further comprising a communication input operable to effect communication of the sweep plan between the controller and the sweep transmitter.
21. The apparatus of claim 20 wherein the communication input comprises a digital serial communication input.
22. The apparatus of claim 18 further comprising a memory coupled to the controller, and wherein the controller is further operable to
obtain the sweep plan from the memory, and
effect communication of the sweep plan to the sweep transmitter.
23. The apparatus of claim 18 further comprising a memory coupled to the controller, and wherein the controller is further operable to
effect communication of the sweep plan from the sweep transmitter communication input, and
provide the sweep plan to the memory.
24. The apparatus of claim 18 further comprising a display, and wherein the controller is further operable to
receive the measurement signals from the measurement circuit,
generate indication signals representative of the measurement signals, and
provide the indication signals to the display.
25. The apparatus of claim 18 wherein the receiver circuit is further operable to
receive an RF sweep signal from the test input, the RF sweep signal corresponding to the sweep plan, and
generate an intermediate frequency signal comprising a plurality temporal segments, each segment corresponding to one of the plurality of frequencies, and wherein the measurement circuit is further operable to generate a measurement signal for
each segment.
26. The apparatus of claim 25 further comprising an analog-to-digital (A/D) converter coupled between the receiver circuit and the measurement circuit, and wherein the circuit includes a digital signal processing circuit.
27. The apparatus of claim 18 wherein the receiver circuit is operable to receive a synchronization signal, wherein the measurement circuit is operable to provide a measurement signal based on the synchronization signal to the controller, and
wherein the controller is operable to generate the sweep signal after a predetermined delay from receiving the measurement signal based on the synchronization signal.
28. The apparatus of claim 18 wherein the measurement circuit is further operable to identify the synchronization signal from the measurement signal based on the synchronization signal and wherein the synchronization signal comprises a
predetermined number of pulses modulated onto a carrier signal having one of the plurality of frequencies.
29. The apparatus of claim 18 further comprising a user input operably connected to the controller, the user input operable to receive input signals representative of a sweep plan, and wherein the sweep plan is based on the received input
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates generally to communication system testing, and more particularly, to frequency sweep testing of communication systems.
BACKGROUND OF THE INVENTION
Cable television distribution networks, or CATV distribution networks, have historically been used to provide a plurality of television signals from a centralized transmitter to a distributed network of subscribers. Such use typically required
only one-way communication, from the centralized transmitter to the subscribers. Recently, however CATV distribution networks have been increasingly employed for two-way communication to facilitate the provision of new services. CATV distribution
networks are desirable for use as two-way communication links because of the bandwidth that is available in the distribution network. CATV distribution networks can support high speed data links that may be used for computer internetworking, home
banking, and even telephony.
All communications, including communications over CATV networks, require a high quality transmission network. Accordingly, CATV service providers closely monitor the operation of the CATV distribution network to ensure that subscribers receive
appropriate signal levels. To ensure quality two-way communications CATV service providers also perform tests to monitor the quality of reverse path transmissions, in other words, transmissions from the subscribers to a centralized receiver.
Unfortunately, most of the problems associated with reverse path transmissions originate within devices and components owned and maintained by CATV subscribers.
In particular, CATV subscribers typically own and maintain the distribution network, or subscriber network, located within their own dwellings. Accordingly, the component quality and condition can vary widely. Moreover, CATV subscribers often
install one-way amplifiers and other components that are not intended for two-way communications. While such components may provide adequate signal levels for receiving television signals, such components are often inadequate for two-way communication
applications.
Accordingly, with the advent of two-way communications using the CATV distribution network, a need has arisen for testing the signal response of subscriber networks to ensure high quality reverse path transmissions. One effective method of
testing the signal response of a network such as a subscriber network is a test known as a frequency sweep test, or simply sweep tesi. A sweep test is a test in which a transmitter is connected to a first end of a system under test and transmits a
signal having a swept frequency over a predetermined frequency range. A receiver that is synchronized with the transmitter then is connected at a second end of the system under test and receives the signal and analyzes the received signal strength at
each of the swept frequencies. The analysis provides the frequency response of the system under test.
CATV service providers have historically used sweep testing to test the forward path signal quality of the CATV distribution network. Several sweep testing systems are known. These systems, such as the one disclosed in U.S. Pat. No.
5,585,842, are primarily intended for a configuration in which the sweep transmitter is installed at the CATV centralized transmitter, and the sweep receiver is installed at a remote test site. Typically, the sweep receiver will be moved from test site
to test site while the transmitter is installed at the CATV centralized transmitter.
One consequence of the above described configuration is that the sweep transmitter must communicate with the sweep receiver to coordinate sweep plan information and normalization measurement information. Sweep plan information is information
that identifies the frequencies to be swept, which can vary from test to test. Normalization measurement information is information identifying the strength of the transmitted sweep signal, which can vary from test to test, particularly over long
periods between tests.
U.S. Pat. No. 5,585,842 teaches the communication of the sweep plan information and normalization measurement information by transmitting a telemetry signal over the CATV network to the sweep receiver. The telemetry signal is a baseband data
signal modulated onto an RF carrier signal. The baseband data signal comprises data representative of the sweep plan and the normalization measurements. The sweep receiver then uses the sweep frequency information in the telemetry signal to identify
the frequencies to be swept, and uses the measurement information to identify the strength of the transmitted signal. To transmit telemetry signals over the CATV network, the sweep transmitter includes circuitry for modulating a digital information
signal onto an RF carrier signal.
Sweep systems of such design are quite adequate for use in configurations in which the sweep transmitter is installed at the head end and the sweep receiver is moved from location to location, as is typical in forward path measurements. Sweep
systems of such design have also been used for testing subscriber networks in the context of reverse path communications. However, such systems are not cost optimal for testing reverse path communications of subscriber networks. In particular, the
telemetry signal transmission capabilities significantly impact the cost of the sweep transmission devices used in such systems. While such costs are easily justified for forward path testing, in which only one sweep transmitter is needed to test an
entire network, such costs are not always justified for reverse path testing of subscriber networks, where a separate transmitter is required for each test.
In particular, to test a subscriber network in isolation, the sweep transmitter and sweep receiver must be installed at each test location. Accordingly, in contrast to forward path distribution network testing, a separate transmitter is required
for each testing operation. To carry out several tests in parallel, or to allow several technicians to have the necessary equipment to carry out such tests, the CATV service provider must stock several sweep transmitters. Such an increase in the number
of transmitters owned by a CATV service provider greatly increases the cost to the CATV service provider. Thus, for reverse path subscriber network sweep testing, a need has arisen for a low cost and low complexity sweep measurement system.
One way of reducing the sweep transmitter cost would be to use a single predefined sweep plan and dispense with normalization measurements, thereby eliminating the need for telemetry signals. Telemetry is necessary, however, to facilitate
flexible and accurate tests. In particular, the normalization measurement information provided through telemetry signals is required for accurate signal response measurements. Without the normalization measurement information, which provides a
measurement of the transmitted signals at the transmission point, operational variances of the sweep transmitter are not accounted for in the measurement thereby causing inaccuracy. In addition, without the sweep plan information, the sweep transmitter
and sweep receiver must rely on a predetermined and inflexible set of frequencies to be swept.
A need therefore exists for a sweep testing system that has the accuracy provided by the use normalization measurement information identifying the strength of the sweep signal at the transmission point, or normalization information, without the
need for providing RF telemetry signals. A need also exists for a sweep testing system that has the flexibility provided by a variable sweep plan without the need for providing RF telemetry signals.
SUMMARY OF THE INVENTION
The present invention fulfills the above stated needs, as well as others, by providing a sweep transmitter and sweep receiver that operate in a configuration mode and a test mode. In the configuration mode, the sweep receiver is connected to
effect direct digital communications with the sweep transmitter, and is further connected to receive RF signals directly from the sweep transmitter. In the configuration mode, the sweep transmitter and sweep receiver coordinate and communicate the sweep
plan. The sweep receiver further takes RF measurements that constitute the normalization measurements. In the test mode, the sweep transmitter and sweep receiver are connected to the system under test. The sweep receiver uses the sweep plan
information and normalization information obtained in the configuration mode to carry out the sweep test. The two mode operation of the present invention sweep plans without the need for transmitting sweep plans as a telemetry signal. The use of stored
normalized values allows for the accuracy afforded by the use of normalization information without relying on telemetry signals to communicate such values over the RF system to be tested.
An exemplary embodiment of the present invention is an apparatus for receiving sweep testing signals and generating frequency response values therefrom. In particular, the apparatus receives sweep testing signals generated in accordance with a
predefined sweep plan by a remote sweep transmitter, the sweep transmitter coupled to a communication system to be tested. The apparatus includes a test input, a controller, a receiver circuit and a measurement circuit.
The test input has a first connection arrangement for connecting to a test output of the sweep transmitter and also has a second connection arrangement for connecting to a terminal of the communication system to be tested. The controller is
operable to generate a sweep control signal responsive to a sweep plan. The receiver circuit has a control input connected to receive the sweep control signal from the controller. and is operable to tune to a plurality of frequencies responsive to the
sweep control signal. The measurement circuit is coupled to the receiver circuit and is operable to generate measurement signals corresponding to the plurality of frequencies.
In accordance with the present invention, the controller is further operable to: receive a first set of measurement signals from the measurement circuit when said test input is connected in the first connection arrangement; receive a second set
of measurement signals from the measurement circuit when said test input is connected in the second connection arrangement; and generate a frequency response based on the first set of measurement signals and the second set of measurement signals.
The above discussed features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE
DRAWINGS
FIG. 1 shows a sweep transmitter 10 and a sweep receiver 20 according to the present invention connected in a first connection arrangement for operation in a sweep configuration mode;
FIG. 2 shows a sweep transmitter 10 and a sweep receiver 20 in a second connection arrangement for operation in a sweep testing mode;
FIG. 3 shows in further detail an exemplary embodiment of a sweep transmitter according to the present invention;
FIG. 4 shows the detailed operation of the controller of the sweep transmitter of FIG. 3 in connection with the generation of sweep signals and synchronization signals;
FIG. 5 shows in further detail a schematic block diagram of a sweep receiver according to the present invention incorporated into a combination meter device;
FIG. 6 shows a flow diagram of the operations carried out by the controller of the combination meter of FIG. 5 in a sweep testing method according to the present invention; and
FIG. 7 shows the detailed operation of the controller of the combination meter of FIG. 5 in connection with the control of the sweep receiver to detect the synchronization signal and the sweep signal generated by the sweep transmitter of FIG. 3.
DETAILED DESCRIPTION
FIGS. 1 and 2 show a sweep transmitter 10 and a sweep receiver 20 according to the present invention connected in two modes of operation. FIG. 1 shows a sweep transmitter 10 and a sweep receiver 20 according to the present invention in a first
connection arrangement for operation in a sweep configuration mode. FIG. 2 shows a sweep transmitter 10 and a sweep receiver 20 in a second connection arrangement for operation in a sweep testing mode. The second connection arrangement is an
arrangement in which the sweep transmitter 10 and sweep receiver 20 are connected to a system under test. In general, prior to connection the system under test as shown in FIG. 2, the sweep transmitter 10 and sweep receiver 20 are connected as shown in
FIG. 1 to communicate a sweep plan and to provide the sweep receiver 20 with normalization measurements.
Referring to FIG. 1, the sweep transmitter 10 includes an RF test output 12, an RF transmitter 14, a transmitter controller 16, and a communication port 18. The RF test output 12 is connected to the RF transmitter 14. The RF transmitter 14 is
further connected to the transmitter controller 16 to receive control signals therefrom. The RF transmitter 14 is an RF circuit operable to generate RF signals including a sweep signal, wherein the sweep signal is an RF test signal in which the
frequency of the RF test signal is swept over time over a predetermined frequency range. The RF transmitter 14 is furthermore operable to generate the sweep signal in accordance with a sweep control signal received from the transmitter controller 16.
The RF transmitter 14 is further operable to, responsive to control signals from the transmitter controller 16, generate a synchronization signal which has a predetermined time delay relationship with the sweep signal. In the exemplary
embodiment described herein, the RF transmitter 14 is operable to generate a synchronization signal at a predetermined time delay relationship with respect to the generation of the sweep signal.
The transmitter controller 16 is a processor circuit that is operable to generate a sweep control signal that corresponds to the frequencies to be swept. In the exemplary embodiment described herein, the transmitter controller 16 is operable to
generate a sweep control signal that identifies a sweep range and a sweep resolution.
Thus, for example, if the controller 16 provided a sweep control signal to the transmitter 14 identifying a sweep range of 5 MHz to 600.2 MHz and a sweep resolution of 129, then the transmitter 14 would generate a sweep signal that first
transmits a test signal at 5 MHz, then transmits a test signal at 9.65 MHz, then transmits a test signal at 14.3 MHz, and so forth, until 600.2 MHz is reached.
The transmitter controller 16 is further operable to generate a synchronization control signal including a synchronization pulse sequence at a predetermined time delay relationship with the sweep control signal.
The transmitter controller 16 is further connected to the communication port 18. The communication port 18 is a digital communication circuit that is operable to provide a communication interface between the controller 16 and the auxiliary
output 19. The communication port 18 in the exemplary embodiment described herein comprises a three-wire (transmit, receive, and ground) communication circuit that implements a simplified RS-232 protocol.
The sweep receiver 20 comprises an RF test input 22, an RF receiver 24, a measurement circuit 525, a receiver controller 28, a communication port 30, and an auxiliary input 32. The RF test input 22 is coupled to the RF receiver 24. The RF
receiver 24 is further coupled to the measurement circuit 26 and the controller 28. The RF receiver circuit is a circuit operable to receive a sweep signal of the type transmitted by the RF transmitter 14.
In particular, the RF receiver 24 is a circuit operable to receive from the RF input 22 a sweep signal comprising an RF test signal in which the frequency of the RF test signal is swept over a predetermined frequency range. To this end, the RF
controller 28 selectively tunes in a time sequential manner to a plurality of frequencies responsive to a sweep control signal received from the receiver controller 28. The RF receiver 24 is operable to provide a substantially constant frequency
intermediate sweep signal having a plurality of temporally adjacent segments, each of which corresponds to one of the swept frequencies.
For example, if the sweep signal is an RF test signal swept in 4.65 MHz increments between 5 MHz and 600.2 MHz, then the intermediate sweep signal includes a first segment corresponding to 5 MHz, a second segment corresponding to 9.65 MHz, a
third segment corresponding to 14.3 MHz, and so forth.
The RF receiver 24 is further operable to receive synchronization signals at a select RF frequency and provide intermediate frequency synchronization signals to the measurement circuit 26.
The measurement circuit 26 is operable to generate a signal level corresponding to a received signal, for example, for each intermediate sweep signal segment and the intermediate frequency synchronization signal. Such sweep measurement circuits
are known in the art. Further detail regarding a suitable measurement circuit is described below in connection with FIG. 5.
The receiver controller 28 is a circuit operable to receive measurement information pertaining and identify a synchronization sequence therefrom. The receiver controller is further operable to generate a sweep control signal at a predetermined
time delay from the detection of a synchronization sequence. The sweep control signal contains information that corresponds to the sweep plan.
The receiver controller 28 is further connected to a communication port 30. The communication port 30 is a device operable to effect communications with the communication port 18 of the sweep transmitter 10. Preferably, the communication port
30 and communication port 18 are operable to effectuate direct communication with each other. Direct communication as defined herein means communication without the intervention of an external communication network. Direct communication between the
communication port 18 and communication port 30 may be accomplished, by way of example, by one or more wires, a coaxial cable, or through a direct RF transmission. Communication through the telephone network, or CATV distribution network, is not
considered to be direct communication.
It is furthermore preferable that the communication port 30 and the communication port 18 be operable to communicate baseband digital signals, thereby eliminating the need for signal modulation equipment.
As shown in FIG. 1, the sweep transmitter 10 is connected to the sweep receiver 20 in the configuration mode through an RF test cable 34 and a digital connection cable 36. Specifically, the RF test cable 34 directly connects the RF test output
of 12 the sweep transmitter 10 to the RF input 22 of the sweep receiver 20, and the digital connection cable 36 directly connects the auxiliary input 19 of the sweep transmitter 10 to the auxiliary input 32 of the sweep receiver 20.
In general, the sweep transmitter 10 and the sweep receiver 20 operate in the configuration mode to establish test parameters for a sweep test of a system to be tested. In particular, the receiver controller 28 obtains a sweep plan from a memory
associated therewith, not shown. The sweep plan contains information that identifies the frequencies to be swept. In the exemplary embodiment described herein, the sweep plan identifies the sweep range and the sweep resolution. The sweep range
identifies the range of frequencies swept, for example, 5 MHz to 600 MHz. The sweep resolution identifies the number of discrete frequencies within the range to which the sweep signal will be set, for example 129. The sweep plan may suitably be entered
into the memory of the receiver controller 28 through a user input device, not shown, or through the communication port 30 from a programming device, not shown.
The receiver controller 28 then commu | | |
