SU777741A1 - Method of measuring non-uniformity of phase-frequency characteristic of magnetic recording apparatus - Google Patents

Description

The invention relates to measuring technique, in particular to means for measuring the parameters of magnetic recording devices on a moving medium, and is used to measure the unevenness of the phase-frequency characteristics of the magnetic recording-reproduction path.

A known method of measuring the unevenness of the phase-frequency characteristics of the magnetic recording-reproduction path, using two harmonic voltages with multiple frequencies as a test signal. Harmonic signals of multiple frequencies from two synchronized generators are fed through a mixer and recording amplifier, providing a linear recording mode, to the recording head.

Playable signals through filters that separate these signals by frequency are fed to two inputs of the oscilloscope [1].

However, this method is suitable for a qualitative comparative assessment of the influence of various parameters on the phase relations in the path, especially with small changes in these parameters, only in the case of linear recording. When recording with saturation, this method cannot be used. thirty

There is also a known method of measuring “NoreTr” ”* of the phase-frequency characteristic of a magnetic recording-reproduction path, in which a sequence of rectangular pulses is recorded on a magnetic medium, then it is reproduced, filtered, and the received signals are analyzed. The reproduced sequence is then passed through a low-pass filter and converted by an analog-to-digital converter. The converted signal is introduced into an electronic computer, where the amplitude-frequency15 phase and phase-frequency components of the spectrum of the reproduced signal are calculated using the fast Fourier transform program, and then the phase-frequency characteristics of the magnetic recording apparatus are calculated [2].

The disadvantages of this method are the complexity of the measurement process, as well as the large error due to the influence of uneven speed of the carrier on the phase-frequency component of the spectrum of the reproduced signal.

The aim of the invention is to reduce errors and simplify the measurement process.

This goal is achieved by the fact that according to the method of measuring the non-uniformity of the phase-frequency characteristic of the magnetic recording-reproduction path, the pulse sequence is recorded with a duty cycle exceeding two units, and after playback, the main frequency of the recorded pulse sequence and one of the even ones are isolated from the received frequency spectrum by filters multiples of it, frequencies, equalize both of these frequencies, and then measure the phase difference between them.

The measurement method is used as follows.

When measuring the non-uniformity of the phase-frequency characteristic of the magnetic recording-reproduction path, a sequence of rectangular pulses with a duty cycle greater than 2 is formed and recorded on a magnetic medium. After reproducing from the signal spectrum, two components are distinguished: one corresponding to the fundamental frequency of the recorded pulse sequence (f ₀ ) and the other corresponding to the frequency of even frequency of the first one (2nf ₀ ; n = 1, 2, ...). Then the frequency f _{0 is} converted to the frequency 2nf ₀ (or vice versa) and the phase difference is measured between the components reduced to the same frequency.

The drawing shows a variant of the device that implements the proposed method.

Using a pulse master oscillator 1, a sequence of rectangular pulses is formed, following with a repetition rate equal to f ₀ and a duty cycle equal to, for example, three. This sequence is recorded in block 2 of the recording-playback on a moving medium, reproduced from it, and then fed to the inputs of two band-pass filters 3 and 4. Filter 3 is tuned to the frequency fo, and filter 4 to the frequency, for example, 2f ₀ .

It is known that in the spectrum of a periodic rectangular signal, the pulse duty cycle of which is not equal to 2, there are always components at even frequencies, the greater the amplitude, the lower the frequency of the even harmonic. Thus, a signal with a frequency of f ₀ is removed from the output of filter 3, and a signal with a frequency of 2f ₀ is output from a filter 4. A signal with a frequency of / o is supplied to a frequency multiplier 5 by two, from the output of which a double frequency signal is taken. The unevenness of the phase-frequency 5 characteristics of the path is measured by a phase meter 6, the inputs of which receive signals from the outputs of the filter 4 and the multiplier 5. The proposed method compares favorably with the simplicity of the measurement process. In addition to Yu, it reduces the magnitude of the measurement error caused by the presence of uneven carrier speed. This is due to the fact that both analyzed components of the spectrum of the reproduced signal 15 are equally affected by the unevenness of the carrier speed, and the differential circuit of the phase meter enables it to be compensated.

pp

Claims (1)

Claim A method of measuring the non-uniformity of the phase-frequency characteristic of a magnetic recording apparatus path, in which a sequence of rectangular pulses is recorded onto a magnetic medium, then it is reproduced, filtered and the received signals are analyzed, characterized in that, in order to simplify the measurement process, the pulse sequence is recorded with a duty cycle exceeding two units, and after playback, the main frequency of the recorded pulse sequence and one of the tnyh, multiples of frequencies equalize both frequency and then measure the phase difference between them. 40 Sources of information taken into account in the examination 1. USSR author's certificate No. 533980, cl. G AND B 27/36, 12.23.74. 45 2. A. Viches and V. A. Smirnov, On the measurement of phase characteristics of a magnetic recording system. Questions of magnetic recording of electrical signals. M., "Communication", 1973, p. 35 (prototype).