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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
stability intensity at the true frequency spatial/spectral locations f 1 or f 2 to the intensity of the intermodulation products at 2 f 1 - f 2 and 2 f 2 - f 1 . spurious undesired, nonharmonically related, nonrandom signals or spectral content generated internal to a nonlinear circuit. Generally, spurious signals are created by internal mixing of multiple input signals, by internally generated oscillations, and by combinations thereof. spurious interrupt rupt. SQ unwanted, random intersqueeze-on a large crimped connector which requires a special press for installation. squirrel-cage induction motor an induction motor in which the secondary circuit (on the rotor) consists of bars, short-circuited by end rings. This forms a squirrel cage conductor structure, which is disposed in slots in the rotor core. See also cagerotor induction motor. SRAM SS7 SSB SSD SSI SSPA See static random access memory. tude may be controlled by adjusting the input DC voltage. squelch to automatically reduce the gain of the audio amplifier of a receiver in order to suppress background noise when no input signal is being received. The circuit performing this function is called the squelch circuit, and it acts as a controllable receiver input switch to allow reception of strong signals and block the weak and noisy signals.
VHF communications
Published in Mike Tooley, David Wyatt, Aircraft Communications and Navigation Systems, 2017
The alternative (and somewhat superior) squelch system involves sensing the noise present at the output of the receiver’s detector stage and using this to develop a control signal which is dependent on the signal-to-noise ratio of the received signal rather than its amplitude. This latter technique, which not only offers better sensitivity but is also less prone to triggering from general background noise and off-channel signals, is often found in FM receivers and is referred to as noise operated squelch.
Quantifying driver cell phone use at signalized intersections using software-defined radio
Published in Traffic Injury Prevention, 2019
Thomas M. Brennan, Joseph E. Jesson, Pedro Gilberto A. Furlanetto
GNU radio (GNURadio n.d.), an open-source SDR Visual Dataflow Language that runs on a Linux operating system was used to monitor cell phone frequencies. Although other cell providers and cell phone types were tested, a representative example of the radio’s visual display of the frequency spectrum fast Fourier transform (FFT) and time waterfall of a bench-tested 836-MHz Verizon cell phone monitored by a directional +11-dBi antenna gain is shown in Figure 1. The FFT is a time record of each frequency measurement with the delta frequency on the x-axis and time in seconds on the y-axis. The FFT intensity is a function of the number of points used to determine the resolution of the frequency visualization. For example, if the bandwidth is 192 kHz and the FFT size is 4,096, then the FFT resolution is 192,000/4,096 = 46.875 Hz/FFT bin. Any cell signals that appear above the amplitude squelch limit but in the cell transmission range by a +20-dB change becomes a trigger event signaling an active session with the cell phone’s BTS. The antenna with directional gain improved the signal-to-noise ratio. The antenna selected offers a directional antenna gain of +11 dBi, and this was observed to improve the signal-to-noise ratio of the RF source emanating from the passing vehicle and through the directional antenna lobe. Future enhancements would include RF energy detection with an adaptive detection threshold for noisy RF environments (Urkowitz 1967). By measuring a +20-dB change in signal level, the waterfall provides an intuitive visualization record of a series of cell frequencies over time (Figure 1). In Figure 1a no cell activity for the bench test phone is present (callout i) at time zero. This correlates to the instantaneous frequency in callout ii.