Frequency counter

About: Frequency counter is a research topic. Over the lifetime, 1056 publications have been published within this topic receiving 6770 citations.

Considerations on the measurement of the stability of oscillators with frequency counters

Abstract: The most common time-domain measure of frequency stability, the Allan variance, is typically estimated using a frequency counter. Close examination of the operation of modern high-resolution frequency counters shows that they do not make measurements in the way commonly assumed. The consequence is that the results typically reported by many laboratories using these counters are not, in fact, the Allan variance, but a distorted representation. We elucidate the action of these counters by consideration of their operation in the Fourier domain, and demonstrate that the difference between the actual Allan variance and that delivered by these counters can be very significant for some types of oscillators. We also discuss ways to avoid, or account for, a distorted estimation of Allan variance

Compensation for Frequency Adjustment in Mobile Communication-Positioning Device With Shared Oscillator

Abstract: In a mobile communication device, a method for compensating for a frequency adjustment in an oscillator shared between a communication circuit and a positioning signal receiver is provided. In one embodiment, the method begins to receive and store a positioning signal at a first time point. When, at a second time point, the operating frequency of the shared oscillator is adjusted, the frequency adjustment is recorded. After the positioning signal is completely received and stored, the processing of the positioning signal takes into consideration the frequency adjustment. In that embodiment, the processing hypothesizes a frequency shift in the received positioning signal. According to another aspect of the present invention, a method for determining the operating frequency of an oscillator detects a beginning time point of a reference signal received by the mobile communication device and enables a counter to count in step with a clock signal derived from the oscillator. When an ending time point of the reference signal is received by the mobile communication device, the count is stopped, and the frequency of the oscillator is determined based on the count in the counter and an expected time that elapsed between the beginning time point and the ending time point.

On the measurement of frequency and of its sample variance with high-resolution counters

Abstract: A frequency counter measures the input frequency ν¯ averaged over a suitable time τ, versus the reference clock. High resolution is achieved by interpolating the clock signal. Further increased resolution is obtained by averaging multiple frequency measurements highly overlapped. In the presence of additive white noise or white phase noise, the square uncertainty improves from σν2∝1∕τ2 to σν2∝1∕τ3. Surprisingly, when a file of contiguous data is fed into the formula of the two-sample (Allan) variance σy2(τ)=E{12(y¯k+1−y¯k)2} of the fractional frequency fluctuation y, the result is the modified Allan variance mod σy2(τ). But if a sufficient number of contiguous measures are averaged in order to get a longer τ and the data are fed into the same formula, the results is the (nonmodified) Allan variance. Of course interpretation mistakes are around the corner if the counter internal process is not well understood. The typical domain of interest is the the short-term stability measurement of oscillators.

Considerations on the Measurement of the Stability of Oscillators with Frequency Counters

Abstract: The most common time-domain measure of frequency stability, the Allan variance, is typically estimated using a frequency counter. Close examination of the operation of modern high-resolution frequency counters shows that they do not make measurements in the way commonly assumed. The consequence is that the results typically reported by many laboratories using these counters are not, in fact, the Allan variance, but a distorted representation. We elucidate the action of these counters by consideration of their operation in the Fourier domain, and demonstrate that the difference between the actual Allan variance and that delivered by these counters can be very significant for some types of oscillators. We also discuss ways to avoid, or account for, a distorted estimation of Allan variance.

Gps synchronized frequency/time source

Abstract: A GPS-based frequency/time source of the present invention provides an accurate, traceable, low-cost reference. In particular, the GPS-based frequency/time source includes a GPS receiver (31), a variable frequency oscillator (35), and a microprocessor (33). The GPS receiver receives and produces as output signals GPS information, whereas the variable frequency oscillator has a frequency control input terminal and produces an output frequency signal, and is coupled to the GPS receiver. The microprocessor is coupled to receive the output signals produced by the GPS receiver and produces an error signal indicative of a difference in frequency between the GPS synchronized frequency and the output frequency signal of the variable frequency oscillator. Circuitry is responsive to the error signal to produce an electronic frequency control signal (37), which is applied to the frequency control input of the variable frequency oscillator so as to cause the difference in frequency to be reduced. In this manner, a low cost oscillator may be employed in such a way as to produce a very accurate output frequency signal.