SU754325A1 - Method of measuring the coefficient of harmonics of four-pole network at the given power level - Google Patents

Description

The invention relates to the radio industry and can be used in the technique of radio measurements.

Known methods for determining the harmonic ratio of a quadrupole, one of which is to calculate the harmonic ratio of the quadrupole

The disadvantage of this method is the accuracy associated with inaccurate knowledge of the non-linearity of the amplitude characteristic of the quadrupole.

The closest in technical to the proposed is a method for measuring the harmonic ratio of a quadrupole, which consists in supplying a single-frequency test signal to a test quadrupole of such a power level at which the voltage of the spectrum indicator noise in the spectral measurement band is: -. can be neglected in comparison ’: with the voltage of the harmonic of the K-th order

2

selective measurement of the voltages of the first harmonic and the harmonic of K —th order H at the output of this quadrupole and the determination of the harmonic coefficient and £ by the formula

The disadvantage of this method is the low accuracy of the measurement of the harmonic coefficient in the region of small signals at the power level, at which at the quadrupole load the noise voltage in the measurement band of the spectral components cannot be neglected compared to the harmonic voltage.

The purpose of the invention is to improve the measurement accuracy.

It is achieved by changing the amplitude of the test signal, selectively measuring the voltage of the first harmonic and the harmonic voltage of the K — th order at the output of the quadrupole, measuring the power of the first harmonic 754325

ki on the load of the quadrupole, and the harmonic coefficient of the K-th order is determined by the formula

.0)

but

- harmonic order;

- the value of the power at which the harmonic factor is determined;

- the value of the power of the first harmonic at the load of the quadrupole CR, the first measurement;

- the value of the power of the first harmonic on the load of the quadrupole in the second dimension;

- voltage of the first harmonic in the first and second measurements;

- harmonic voltage of the K-th order in the first and second measurements.

Method harmonic coefficient measurements consist in ²⁵ nick selective measurement of the output voltages of the first quadrupole harmonic and harmonics of order K with alternately applied to the input of the quadripole audio frequency signal, but of different power levels and determining the harmonic content of the above formula. Moreover, the voltage value of the test signal during the second measurement should be the maximum allowable, that is, the signal should not exceed the upper limit of the linear dynamic range of the K-th order in the overload threshold of the quadripole under study.

The following inequality must be satisfied:

Where

4 * ⁴ 40 "(4)] \ (1)

where u

Δ - overload threshold, dB.

The error in determining ί _{β>) ο} πο the proposed method depends on the rational choice of the powers of the fundamental tone P _o , ₄ , P ^.

Practical selection of the range of values of ^p o for which the determination of the harmonic coefficients is advisable to carry out the proposed method. By definition, the harmonic coefficient at power 10

15

20

thirty

35

40

45

the basic pitch основногоθ without noise is

In the presence of spectrum indicator noise, since the phase correlation of the harmonic power and noise power is absent, we have the harmonic coefficient in the form

where is the noise power in the measurement band of a non-linear product.

Then, given that the measurement error of the harmonic coefficient in the presence of spectrum analyzer noise is

'Chaon & and ¹ )' “KAO ¢ 3)

and what

/ Chg ^<o

we have that with the permissible error value in dB due to the noise of the spectrum indicator ϋ ⁴ ** '(for example,

~ 0.2 dB) and a given maximum linearity level B ^ lnp'n which we want to determine so that the error due to noise does not exceed

dB, therefore, the method of determining the harmonic coefficient should be applied when -

p _w - JSC "

, 01CH ”/ A0. four ·

From the post-expression, it follows that the smaller the ΰ-ϊ ”, the greater the noise power of the Hz spectrum indicator, and finally, the higher the linearity level ( _Kd4GP -, _n <0), the greater the pitch power value at the load.

The practical choice of the value of the first harmonic power during the first measurement of the harmonics RD is necessary when performing. of the way. From equality (3) it follows that for a given error due to noise b ⁴ , much less than the error in determining the harmonic coefficient, it is necessary to choose P _l gac, so that

where - the average value of the square

noise voltage per unit frequency band of measurement;

five

754325

is the voltage amplitude of the Kth order harmonic in the first measurement.

Thus, with the known noise of the spectrum indicator and the allowable contribution of

The error due to the noise power of the spectrum indicator in the total error in determining the harmonic coefficient, inequality (4) allows the correct choice of the amplitude of the harmonic and the corresponding power of the first harmonic on the load in the first dimension.

Selection of the power of the first harmonic on the load during the second measurement

harmonics is based on limiting it to the value of the upper limit of the linear dynamic range at a given overload threshold. The upper limit of the linear dynamic range is 20 one of the parameters characterizing the nonlinear two-port network, amenable to theoretical and experimental definition. According to the definition, the upper limit of the linear dynamic range of overloads is the power of the fundamental tone at the load, corresponding to a given deviation of the dependences of the harmonics coefficient of the K-th order () on the level, powerful

These signals are at the load, expressed in logarithmic units of measure (dB _m ) from linear. Practically, when choosing, it is possible to use the equivalent condition (2), which means that 35 if R _{g is} chosen so that W ^ / M *. in the second reading it does not exceed units, then the power of the first harmonic in the second dimension is no more than the upper limit of the linear dynamic range, and the definition of the harmonic coefficient and formula (1) is reliable.

The proposed method makes it possible to avoid the use of spectrum indicators 45 with a large dynamic range and high sensitivity, which simplifies measuring equipment, expands the measurement range of harmonic coefficients in the small signal area and reduces the error in their determination.

Claims (1)

A method for measuring the harmonic ratio of a quadrupole at a given power level, consisting in supplying a single test frequency signal to a tested quadrupole, selectively measuring first-harmonic voltages and harmonics of the K-th order at the quadrupole output, and measuring the first-harmonic power at the quadrupole load, which is different I, in order to increase the measurement accuracy, change the amplitude of the test signal, selectively measure the voltage of the first harmonic Voltage harmonics K-th order output quadripole measured power of the first harmonic of the quadrupole load, and harmonic distortion K-th order is determined by the formula: Ah ’ where K is the harmonic order; p is the value of the power at which the harmonic coefficient is determined; • - the value of the power of the first harmonic on the load of the quadrupole at the first measurement - ν ,, ν ': nii; - the value of the power of the first harmonic on the load of the quadrupole in the second dimension; voltage of the first harmonic in the first and second measurements; voltage harmonics of the K-th order in the first and second measurements.