Method of and means for measuring the level of test signals over selected wide band frequency ranges
First Claim
1. A method of determining the level of received test signals over selected frequency ranges of different bandwidths B bounded by a lower limiting frequency f'"'"' and an upper limiting frequency f", comprising the steps of:
- establishing a frequency window of fixed width b≦
B within a selected frequency range;
shifting said window in the presence of said test signals across the selected range with the midfrequency fm of said window varying in a sweep cycle between f'"'"'+b/2 and f"-b/2;
integrating the RMS values of signal amplitudes appearing in said window throughout the sweep cycle;
shifting at least one of said limiting frequencies for changing to a different frequency range; and
measuring the integrated RMS values of each frequency range after multiplying said values with a corrective factor proportional to the bandwidth B of the respective frequency range.
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Abstract
To measure the level of test signals over a frequency range of variable bandwidth B, bounded by a lower frequency f'"'"' and an upper frequency f", these signals are heterodyned with a variable modulating frequency to produce a frequency spectrum encompassing the pass band of an intermediate-frequency filter of fixed bandwidth b≦B, centered on a frequency fc. By periodically shifting the modulating frequency between a minimum value of f'"'"'-fc +(b/2) and a maximum value of f"-fc -(b/2), either continuously or in steps, the frequency range of bandwidth B is scanned by a window of bandwidth b transposed to the pass band of the filter as the midfrequency fm of the window varies in a sweep cycle between f'"'"'+b/2 and f"-b/2. The signal level in the output of the filter, integrated over the sweep cycle, is weighted with a corrective factor B/b.
10 Citations
14 Claims
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1. A method of determining the level of received test signals over selected frequency ranges of different bandwidths B bounded by a lower limiting frequency f'"'"' and an upper limiting frequency f", comprising the steps of:
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establishing a frequency window of fixed width b≦
B within a selected frequency range;shifting said window in the presence of said test signals across the selected range with the midfrequency fm of said window varying in a sweep cycle between f'"'"'+b/2 and f"-b/2; integrating the RMS values of signal amplitudes appearing in said window throughout the sweep cycle; shifting at least one of said limiting frequencies for changing to a different frequency range; and measuring the integrated RMS values of each frequency range after multiplying said values with a corrective factor proportional to the bandwidth B of the respective frequency range. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A system for determining the level of received test signals over selected frequency ranges of different bandwidths B, comprising:
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input means for receiving test signals lying within a selected frequency range; filter means having a pass band of substantially constant width b≦
B outside the selectable frequency ranges, said pass band having a fixed center frequency fc ;a generator of variable modulating frequency, ranging in a recurrent sweep between a minimum value f'"'"'-fc +b/2 and a maximum value f"-fc -b/2 wherein f'"'"' is a lower limiting frequency and f" is an upper limiting frequency of the selected range; mixer means connected to said input means upstream of said filter means and further connected to said generator for heterodyning said test signals with said modulating frequency to generate beat-frequency oscillations passed by said filter means, said beat-frequency oscillations corresponding to test signals present in a frequency window of width b centered on a midfrequency fm ; scanning means for periodically varying said modulating frequency between said minimum and maximum values, thereby shifting said midfrequency fm between limits f'"'"'+b/2 and f"-b/2, said scanning means including a range selector operable to vary at least one of said limiting frequencies; output means including rectification, storage and weighting circuitry connected to said filter means for integrating the RMS values of signal voltages appearing within said frequency window throughout at least one sweep cycle and multiplying said signal voltages by a corrective factor proportional to said bandwidth B; and indicator means connected to said circuitry for giving a reading of the integrated signal voltages so multiplied, said range selector being coupled with said output means for automatically modifying said corrective factor in conformity with the bandwidth B of the selected range. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification