SU974291A1 - Tracking generator for spectrum analysis - Google Patents

Description

one

The invention relates to electrical measuring equipment and is intended for Precision measurements of the amplitudes of the spectral components of radio signals, for accurate transmission values of four poles (amplitude-frequency characteristics), sensitivity measurements, nonlinear distortion, CWS, antenna parameters, calibration of measuring instruments in a wide frequency range and etc.

Spectrum analyzers are known using a tunable filter. The selective filter is sequentially tuned in the working frequency range synchronously with the sweep of the oscillographic and indicator. At the same time, the spectrum of the studied is reproduced on the screen. signal ul.

Despite its simplicity, this 1H method is limited by the difficulty of obtaining high resolution and a large dynamic range of a tunable selective filter in a wide frequency range, as well as by the complexity of implementing a tracking oscillator tuned synchronously with the frequency of a spectrum analyzer.

A spectrum analyzer is also known in accordance with a superheterodyne transform circuit with a following generator, whose amplitude is varied by an attenuator placed at the output of the t-2 3 tracking generator.

A disadvantage of the known construction of the following generator is the low accuracy of the output level variation in a wide range.

ts frequencies, which are caused by significant attenuator errors, as well as changes in the output impedance of the following generator when the output signal level is switched, which increases the measurement error of the CWS, reflection coefficients, etc.

Claims (2)

The purpose of the invention is to improve the accuracy of setting the amplitude of the output-signal of the following generator while maintaining a constant impedance at the eiix) output. This goal is achieved so that a duty ratio generator connected between the reference generator and the selective filter is inserted into a tracking generator for a spectrum analyzer containing a series-connected reference oscillator, a selective filter, a mixer and a low-pass filter. The operation of the device is based on the fact that two or several pulse sequences with predetermined duty cycles are formed from the frequency of the reference signal, the frequency of fpg 14 which is converted in the mixer by the local oscillator according to the law of P, the difference of the amplitudes at the output of tracking for two pulse sequences corresponds to the calculated value (the dependence of the amplitude of the N-th harmonic on the duty cycle). The drawing shows a functional diagram of the following generator. The device includes serially connected reference generator 1, shunt generator 2 and selective filter 3, the output of which is connected to the signal input of mixer 4, to the heterodyne input of which the analyzer's output is connected, to the output of mixer 4 low-pass filter 5, which output is is an output of a tracking generator. The device works as follows. The frequency of the reference signal from the output of the reference generator 1 arrives at the input of the driver 2 of the duty cycle. The logical construction of a form5) o "atel 2 allows us to produce two (or several) pulse sequences with a period equal to (different porosity over this period. Thus, at the output of the selective filter 3, the signal at a frequency of which is proportional to the amplitude of the harmonic A pulse sequence. As is known, the amplitude of the nth harmonic of a periodic sequence of rectangular pulses with amplitude E, duration T and repetition period Tf is defined by the expression 1 Using the indicated dependence, we can find the calculated difference of this harmonic for several values of duty ratio. Thus, the input of the mixer 4 receives the signal of the frequency “uC exactly and; by the known difference in amplitudes ... After converting this frequency to the output frequency of the next generator j. J. in mixer 4 at output 4 of 1 liter 5 signals are made whose frequency fc coincides with the frequency of the spectrum analyzer and has an amplitude equal to ,, KA ,, where K is the conversion loss in the mixer. Solving the amplitudes of signals from the clock iH) (1). (1) 1. h -t toto fe g equals (H) A (H). (P) 1 1 -I is known in the whole range, i.e. exactly the operating frequencies of the tracking generator. Thus, by switching the mode of operation of the duty cycle generator, it is possible to change the amplitude of the output signal of the tracking generator by a precisely specified amount in a wide frequency range without changing the output impedance. The following generator for a spectrum analyzer containing a series-connected reference oscillator, a selective filter, a mixer and a low-pass filter, characterized in that, in order to improve the accuracy of setting the amplitude of the output signal, a duty ratio generator is inserted between the reference oscillator and the selective generator. filter. Sources of information taken into account in the examination 1. V. Martshov, Yu. I. Selikov. Panoramic receivers and spectrum analyzers, M., Sovetskoye Radio, 1964, 2. Instrument for the study of amplitude-frequency characteristics X1-46, ЦОО.400.142,