Superheterodyne Radio Tuning Against Image Frequency Peaks
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Solution Overview
Problem
The super heterodyne system in radio wave receiving apparatuses faces challenges in obtaining the correct tuning point for the desired frequency, often due to interference from image frequencies, which can prevent accurate tuning of the tuning circuit.
Innovation Solution
A radio wave receiving apparatus is designed with a local oscillator, frequency converting unit, feedback loop, and control unit that detects the level of intermediate frequency signals to adjust the tuning circuit's frequency characteristics, allowing the system to differentiate between desired and image frequencies by selecting the appropriate tuning point based on the relationship between the local oscillation frequency and the desired wave frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a super heterodyne system is used for radio wave reception, then frequency conversion capability is improved, but image frequency interference occurs preventing correct tuning point acquisition
Solution Approach 1:
The patent segments the tuning process into two distinct phases: a first tuning process that identifies candidate tuning points including image frequencies, and a second tuning process that selects the correct tuning point by comparing signal levels. This segmentation allows the system to handle image frequency interference by separating the broad search function from the precise selection function.
Solution Approach 2:
The patent performs preliminary action by conducting the first tuning process to identify all candidate tuning points (including image frequencies) before executing the second tuning process. The control unit stores signal level information from the first tuning process and uses it to guide the second tuning process, ensuring that the correct tuning point is selected based on pre-analyzed data.
2Device complexity
If automatic tuning is performed without feedback control, then device complexity is reduced, but tuning precision deteriorates due to image frequency interference
Solution Approach 1:
The patent implements feedback control by having the control unit store signal level information from the first tuning process and use it to guide the second tuning process. The system continuously monitors signal levels at candidate tuning points and adjusts the tuning circuit based on this feedback to identify the correct tuning point that maximizes the desired signal while minimizing image frequency interference.
3Reliability
If the tuning circuit is adjusted to maximize detected signal level, then receiving sensitivity is improved, but image frequency interference prevents identification of the correct tuning point
Solution Approach 1:
The patent applies dynamics by implementing a two-stage tuning process that adapts to different tuning requirements. The first tuning process dynamically identifies all candidate points, and the second tuning process dynamically selects the optimal point based on stored signal level information. This dynamic approach allows the system to differentiate between image frequencies and the desired signal by comparing relative signal levels at different tuning points.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the apparatus to accurately tune the circuit to the desired frequency, reducing the impact of image frequencies and ensuring reliable reception of radio waves, even in systems with super heterodyne configurations.
Implementation Method 1
a frequency converting unit for mixing the local oscillation signal generated by the local oscillator with the signal received through the antenna, thereby converting the received signal into an intermediate frequency signal
Data Source
AI summary
A radio wave receiving apparatus is provided with a tuning circuit for bringing a receiving frequency of an antenna tuned in to a frequency of a desired wave, a frequency converting circuit for mixing a local oscillation signal with the signal received through the antenna, thereby converting the received signal into an intermediate frequency signal, a feed back loop including at least a portion of the tuning circuit for feeding back the received signal, a controller for detecting a level of the intermediate frequency signal to change a frequency characteristic of the tuning circuit, thereby obtaining a tuning point corresponding to the desired wave, wherein, the controller brings the feed back loop in operation, thereby changing the frequency characteristic of the tuning circuit, and when two peaks of a level of the received signal are detected while the frequency characteristic of the tuning circuit is changed, the controller selects as a tuning point corresponding to the desired wave a tuning point at which one of the two peaks of the level of the received signal corresponding to a high-low relationship between the predetermined frequency of the local oscillation signal and the frequency of the desired wave is detected.