Receiver Squelch Gating with Delayed Threshold Switching
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Solution Overview
Problem
Existing squelch gating systems in digital receivers experience short-time reversals of audio signal switching due to random peaks in the squelch signal, leading to unwanted muting and delayed reaction times, which deteriorate the time behavior of the squelch detector.
Innovation Solution
The method involves delaying the start and end points of audio signal gating by specific delay times to prevent short-time reversals, with optional adjustments to the time intervals and fading times to optimize the timing of gating, ensuring accurate and timely switching without delaying the squelch signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the time constant of the integrating digital filter is increased to avoid short-time reversals of audio signal switching, then the stability of the squelch signal is improved, but the time behavior of the squelch detector deteriorates due to delayed reaction
Solution Approach 1:
The patent divides the squelch signal processing into two independent paths: a fast path that provides immediate squelch control with short time constant, and a slow path that generates a smoothed squelch signal with long time constant for stability. The audio signal gating is controlled by the fast path while the slow path provides stability feedback, eliminating the need to choose between stability and fast response in a single filter.
2Reliability
If the time constant of the digital filter is set between 5-10 ms to average random peaks, then the reliability of audio signal gating is improved, but the time behavior deteriorates due to delayed squelch signal response
Solution Approach 1:
The patent introduces a second smoothing filter as an intermediary element that processes the squelch signal separately from the audio gating control path. This intermediary filter with long time constant (5-10 ms) smooths the squelch signal for reliable gating decisions without affecting the fast response of the audio signal gating, which is controlled by the unsmoothed or fast-smoothed squelch signal.
Data Source
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AI summary
A Method and an apparatus for squelch gating a receiving signal depending on the level of phase noise in said receiving signal determines sampled amplitudes (mn) and sampled phases (ϕn) of said receiving signal (xn), determines sampled phase noise (pn) by differentiating subsequent sampled phases (ϕn), determines a squelch signal (sn) by rectifying and averaging said sampled phase noise (pn), determines a start point (SPG1,SPG2,SPG3,SPG4) of gating after a rising of said squelch signal (sn) above a higher threshold (Shigh) delayed by a first delay time (TD1), determines a end point (EPG1, EPG2, EPG3, EPG4) of gating after a dropping of said squelch signal (sn) below a lower threshold (Slow) delayed by a second delay time (TD2) and gates said sampled amplitudes (mn) from said start point (SPG1, SPG2, SPG3, SPG4) of gating until said end point (EPG1, EPG2, EPG3, EPG4) of gating.