TRANSMITTER CALIBRATION SYSTEM

• US 20130082687A1
• Filed: 09/29/2011
• Published: 04/04/2013
• Est. Priority Date: 09/29/2011
• Status: Active Grant

• Current Assignee: GatesAir Incorporated (Groupe Sipromad SA)
• Original Assignee: Imagine Communications Limited (Gores Broadcast Holdings LLC)
• Inventors: Craft, Tracee, Chizevsky, William T.
• Granted Patent: US 8,803,505 B2
• Time in Patent Office: Days
• US Class Current: 324/120
• CPC Class Codes: G01R 27/06 Measuring reflection coefficients; Measuring standing-wave ratio
• CPC Class Codes: G01R 27/32 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence
• CPC Class Codes: H04B 17/103 Reflected power, e.g. return loss
• CPC Class Codes: H04B 17/13 of power amplifiers, e.g. gain or non-linearity
• CPC Class Codes: H04B 17/18 Monitoring during normal operation

Abstract

Systems and methods are provided for calibrating a transmitter system. A directional coupler is configured to provide a first signal representative of a forward power of an RF signal and a second signal representative of a reflected power of the RF signal. A splitting assembly is configured to generate respective third and fourth signals, each representative of the forward power, from the first signal. A switching assembly is configured to select between the second signal and the third signal. A system control is configured to determine an associated power of each of the fourth signal and a signal provided by the switching assembly.

Claims

1. A transmitter system comprising:

a directional coupler assembly configured to provide a first signal representative of a forward power of an RF signal and a second signal representative of a reflected power of the RF signal;

a splitting assembly configured to generate respective third and fourth signals, each representative of the forward power, from the first signal;

a switching assembly configured to select between the second signal and the third signal; and

a system control configured to determine an associated power of each of the fourth signal and a signal provided by the switching assembly.

2. The system of claim 1, the directional coupler assembly being implemented as a printed circuit board assembly comprising:

a directional coupler configured to provide the first signal at a first port and the second signal at a second port;

a first fixed attenuator operatively connected to the first port; and

a second fixed attenuator operatively connected to the second port, the first and second attenuators being configured to provide a same amount of relative decrease in respective signal powers of the first and second signals.

3. The transmitter system of claim 1, the splitting assembly comprising an RF signal splitter configured to generate the third and fourth signals from the first signal, a first attenuator configured to reduce the third signal to an appropriate level for analysis at the system control, and a second attenuator configured to reduce the fourth signal to an appropriate level for analysis at the system control.

4. The transmitter system of claim 1, the system control comprising a comparator that receives the second signal and compares it to a threshold value representing a maximum permissible value for the reflected power.

5. The transmitter system of claim 4, the system control comprising a microcontroller and a digital-to-analog converter, the microcontroller providing the threshold value to the comparator through the digital-to-analog converter and the comparator providing an output to the microcontroller.

6. The transmitter system of claim 1, the system control comprising a first root mean square (RMS) detector to determine an RMS power of the fourth signal and a second root mean square (RMS) detector to determine an RMS power of the signal provided by the switching assembly.

7. The transmitter system of claim 6, the system control comprising a first analog-to-digital converter to provide a first digital value from the RMS power of the fourth signal to an microcontroller and a second analog-to-digital converter to provide a second digital value from the RMS power of the signal provided by the switching assembly to the microcontroller.

8. The transmitter system of claim 6, the microcontroller being configured to correct each of the first digital value and the second digital value for a frequency response of the directional coupler assembly.

9. The transmitter system of claim 1, further comprising:

a second directional coupler assembly configured to provide a coupled signal representing the forward power; and

an external power meter configured to determine a value for the forward power from the coupled signal.

10. A method for calibrating a power monitoring system for a radio frequency (RF) transmitter comprising:

providing a first signal, representing a forward power of the transmitter;

providing a second signal, representing a reflected power of the transmitter;

splitting the first signal to provide a third signal and a fourth signal;

providing each of the fourth signal and the second signal to a system control when the system is monitoring the reflected power; and

providing each of the fourth signal and the third signal to the system control when the system is performing a calibration of a reflected signal path.

11. The method of claim 10, wherein providing each of the fourth signal and the third signal to the system control when the system is performing the calibration of a reflected signal path, comprises controlling a switching assembly to sample the third signal when the system is performing the calibration.

12. The method of claim 10, wherein performing a calibration of the reflected signal path comprises:

operating the transmitter at a first power level;

sampling the third signal at the first power level to produce a first sample;

operating the transmitter at a second power level, representing an operating level of the transmitter;

sampling the third signal at the second power level to produce a second sample;

and

evaluating the first sample and the second sample to construct a range of acceptable values for the second signal.

13. The method of claim 12, wherein evaluating the first sample and the second sample comprises determining a slope value as the ratio of the difference between the first sample and the second sample to a difference between the first power level and the second power level.

14. The method of claim 13, further comprising conducting a second calibration process while the transmitter is operating, the second calibration process comprising:

sampling the third signal to produce a calibration sample; and

determining a new range of acceptable values for the second signal from the calibration sample and the determined slope value.

15. The method of claim 14, further comprising providing a signal to the system control from a remote location to perform the second calibration process.

16. The method of claim 13, further comprising determining a reflected power fault threshold from the second sample.

17. The method of claim 10, further comprising performing a frequency correction of the second signal according to a frequency response of the received signal path.

18. The method of claim 10, further comprising:

comparing the second signal to a reflected power fault threshold at a comparator; and

ceasing transmission of the RF signal if the second signal exceeds the reflected power fault threshold.

19. A transmitter system comprising:

a directional coupler assembly, implemented as a printed circuit board and comprising;

a directional coupler configured to provide a first signal representative of a forward power of an RF signal at a first port and a second signal representative of a reflected power of the RF signal at a second port;

a first fixed attenuator operatively connected to the first port; and

a second fixed attenuator operatively connected to the second port, the first and second attenuators being configured to provide a same amount of relative decrease in respective signal powers of the first and second signals;

a splitting assembly configured to generate respective third and fourth signals, each representative of the forward power, from the first signal;

a switching assembly configured to select between the second signal and the third signal; and

a system control configured to determine an associated power of each of the fourth signal and a signal provided by the switching assembly, the system control comprising;

a first root mean square (RMS) detector to determine an RMS power of the fourth signal;

a second root mean square (RMS) detector to determine an RMS power of the signal provided by the switching assembly;

a microcontroller;

a first analog-to-digital converter to provide a first digital value from the RMS power of the fourth signal to the microcontroller; and

a second analog-to-digital converter to provide a second digital value from the RMS power of the signal provided by the switching assembly to the microcontroller;

wherein the microcontroller is configured to correct each of the first digital value and the second digital value for a frequency response of the directional coupler assembly.

20. The transmitter system of claim 19, the system control further comprising a comparator that receives the second signal and compares it to a threshold value representing a maximum permissible value for the reflected power.