SU375621A1 - DEVICE MEASUREMENT GROUP DELAY - Google Patents

Description

one

The invention relates to the field of radio measurements.

Devices are known that implement a method for measuring a group delay in terms of a delayed envelope of a group, for example, dual frequency signal. The method makes it possible to measure the absolute values of the group delay with high accuracy. Dispersion characteristic (group delay versus frequency) is usually obtained by sweeping (frequency sweep) with access to a recorder or oscilloscope screen. However, with group delay of ten to hundreds of microseconds, it is difficult to ensure high accuracy of reference. In this case, it is advisable to record the difference dispersion characteristic, which shows the deviation of the delay line dispersion from the specified one. At present, in the absence of a reliable standard, the differential dispersion characteristic is obtained as follows. Accurate measurements are made at fixed frequencies, the deviations are calculated, the intermediate values are approximated, and a differential dispersion characteristic is plotted graphically. The method is laborious and does not give an idea of the dispersion at intermediate points.

The purpose of the invention is to improve measurement accuracy.

This is achieved by the fact that one of the outputs of the generator of a two-frequency signal is directly and the other through the reference delay line is fed to an additional adder, the output of which is connected to the input of the detector.

The drawing shows a block diagram of the proposed device.

Harmonic oscillations are generated by tunable oscillators / and 2. The frequency difference of the oscillators during the measurement process is kept constant.

The measuring signal in the form of the sum of two continuous harmonic oscillations from the output of the adder 3 is fed to the input of the dispersion line 4 delays (DLZ) under study. After passing through the DLZ 4 dual-frequency signal, its envelope is highlighted by detector 5, which is connected to the DLZ output. The output of the detector is connected to one of the inputs of the phase meter 6. The phase of the envelope of the two-frequency signal at the output of the SLP with respect to the envelope of the two-frequency signal at its input will be

A- (f) (0,

where / 1/2 - fi const in the measurement process, gr (/) - group time delay of the measurement signal at the frequency /.

The 30 delay reference line 7, the adder 5 and the detector 9 form a circuit for forming the supportive signal. The output of the generator 1 is connected to the adder 8. The generator 2 is connected to the adder 8 via the reference delay line 7. The phase of the envelope of the two-frequency signal at the output of the adder 8 with respect to the phase of the envelope of the two-frequency signal at the output of the adder 3 (at the output of the LLL) is A, (f) z2uf.4, where 3 is the delay time of the reference line 7. But f2 fo +. Therefore, (f) 27: fo.4 + cp, fo: F-t, const. The envelope of the reference dual frequency signal is detected by the detector 9, which is connected to the second input of the phase meter 6. The voltage at the output of the phase meter is proportional to the phase difference between the envelopes of the delayed and reference signals. In order for the voltage at the output of the phase meter to be proportional to the deviations of the dispersion of the delay line from the linear one, the phase of the reference voltage must change in accordance with the calculated value of the linear dispersion of the DLA under study. 30 35 This can be implemented by appropriately adjusting the delay time of line 7 and the difference frequency of generators 1 and 2. In practice, it is advisable to change the delay time of line 7 in steps, and the difference frequency F smoothly. The initial phase is compensated by the phase shifter 10. If the given dispersion characteristic of the investigated delay line is different from linear (quadratic, cubic, etc.), then the reference delay line 7 must be dispersive. Its dispersion characteristic should have a curvature an order of magnitude lower than the curvature of the dispersion characteristic of the delay line under study (linear, quadratic, etc.). The proposed measurement method can be easily implemented to control lines with a linear dispersion. In this case, the delay time of the reference line does not exceed tenths of a microsecond, and it can be made in the form of a segment of a high-frequency cable. The subject of the invention is a group delay measurement device comprising a dual frequency signal generator, an adder, two detectors and a phase meter, characterized in that, in order to improve measurement accuracy by measuring dispersion deviations from a given one, one of the outputs of the dual frequency signal generator is straight and delays are applied to an additional adder, the output of which is connected to the detector input.