FM Receiver Bandwidth Control via Adjacent Channel Modulation
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Solution Overview
Problem
In FM radio broadcast systems, accurately selecting the bandwidth to avoid interference from adjacent channels is challenging, as existing methods can lead to latch-up issues and incorrect energy measurements, especially in environments with close channel spacing standards like Europe and Asia, where overlap is common, and the use of high-end converters is costly.
Innovation Solution
The solution involves measuring the modulation level of adjacent channels to dynamically set the bandwidth for the desired channel, using an inverse relationship to determine a more narrow or wide bandwidth setting based on the adjacent channel's modulation level, and incorporating feedback from distortion measurements to optimize the bandwidth selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a narrow bandwidth is selected for the measured channel to avoid adjacent channel interference, then the detector can avoid overlap and interference from adjacent broadcast FM signals, but the detector would indicate low modulation for this channel, causing further problems with deviation measurements and potentially leading to latch-up issues
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring the modulation level of the adjacent channel signal itself, rather than directly measuring the desired channel with a narrow bandwidth. This intermediary measurement allows the system to infer about adjacent channel characteristics without being misled by the desired channel's modulation content, thus avoiding the latch-up problem while still achieving interference rejection.
Solution Approach 2:
The system uses feedback from measuring the adjacent channel's modulation level to dynamically adjust the bandwidth setting for the desired channel. By continuously monitoring the adjacent channel's modulation characteristics and using this information to control the measurement bandwidth, the system maintains reliable operation while avoiding interference from adjacent channels.
2Measurement precision
If a wider bandwidth is used to measure the desired channel to ensure accurate modulation detection, then the detector can capture all energy of the desired channel, but the detector would capture energy from adjacent channels, leading to incorrect measurements and potential latch-up
Solution Approach 1:
Instead of directly measuring the desired channel with a wide bandwidth (which would capture adjacent channel energy), the patent uses the adjacent channel signal as an intermediary to infer information about the desired channel's modulation characteristics. This indirect approach allows accurate modulation detection without capturing harmful adjacent channel energy.
Solution Approach 2:
The patent inverts the conventional measurement approach by measuring the modulation level of the adjacent channel rather than the desired channel. This inversion allows the system to determine bandwidth settings based on adjacent channel characteristics, which are easier to measure accurately without contamination, and then apply this information to control the desired channel's reception.
3Measurement precision
If high-end AC-DC converters are used to measure deviation and achieve stable results, then the deviation measurement can be more accurate and stable, but the expense is excessive for many applications
Solution Approach 1:
The patent employs a low-cost digital signal processing approach using standard ADC converters combined with algorithmic methods to achieve stable deviation measurements. Instead of relying on expensive hardware like QPD 25-12 Series converters, the system uses software-based processing techniques that can be implemented with inexpensive components while maintaining measurement accuracy and stability.
Solution Approach 2:
The patent replaces expensive hardware-based deviation measurement systems with a digital signal processing approach. By using digital signal processing techniques to analyze the modulation level of adjacent channels and infer desired channel characteristics, the system eliminates the need for costly analog-to-digital converters while achieving comparable or superior measurement stability.
Data Source
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AI summary
Exemplary aspects are directed to FM-radio circuitries and systems in which, at the receiving end of an FM broadcast transmission, circuitry is used to set the bandwidth for receiving the desired channel of the FM broadcast signal based on measured signal properties of immediately-adjacent channel(s) and based on an inverse relationship between an indication of FM modulation level of the other channel(s) and the amount for which the bandwidth is to be set. FM-signal processing circuitry suc as logic/CPU circuitry, then receives the desired channel, including information carried by the FM broadcast signal, in response to setting the bandwidth based on the measured signal properties.