SU1327023A1 - Method of measuring spectral density of noise level and noise coefficient of four-terminal network - Google Patents

Abstract

This invention relates to the field of radio measurements. The goal is to increase the reliability of measurements of the spectral density of the noise intensity and the noise factor of quadrupoles (PR), an alternate PR in the conditions of a polyharmonic operating signal with an amplitude of one of the harmonics (d) beyond the linear portion of the amplitude characteristic of the PR. To achieve it, a harmonic signal with a power level and frequency equal to the operating conditions of the largest G input signal is supplied by the measurement method, the narrowband envelope is measured, the frequencies of the output signal of the PR signal in a certain range and its constant component are measured levels, an amplitude-modulated signal from a harmonic frequency envelope and a known modulation depth is supplied to the PR, the modulation depth of the output signal of the PR is measured, and the calculated average noise parameters are determined. These measurements are repeated twice, changing the frequency, and calculate the values of the spectral density of the noise intensity and the noise figure of the PR. In the description of the invention, mathematical expressions are given to calculate the indicated values. 3 il. from 9 (L 00 you to SA9

Description

The invention relates to a technique of radio measurements and can be used to measure the spectral density of noise intensity and noise figure of active two-port band-pass actives, for example, antenna amplifiers and high-frequency amplifiers of radio receiving devices, traveling wave tubes, intermediate frequency amplifiers.

The purpose of the invention is to increase the reliability of measurements of the spectral density of the noise intensity and noise coefficient of quadrupoles describing a quadrupole under the conditions of a polyharmonic operating signal with an amplitude of one of the harmonics outside the linear portion of the amplitude characteristic of the quadrupole.

Figure 1 is a diagram of an apparatus for implementing a measurement method; 2 and 3, respectively, the spectral characteristic of the test signals and their envelopes at different points in time.

A device for implementing the method comprises a series-connected high-frequency generator, an amplitude modulator 2, a quadrupole under study 3, an amplitude detector 4 and a constant voltage voltmeter 5 to the output of the amplitude detector 4 A selective voltmeter 6 is also connected The device also contains a low-frequency generator 7 and a source 8 DC voltage, connected respectively to the first and second inputs of the adder 9, the output of which is connected to the control platoon of the amplitude modulator 2.

The essence of the method can be seen on the example of the operation of the device for its implementation.

First, set the frequency and power of the signal generator 1 is equal to f - and 1.21 P

6x

where is fo and p

VC

, f-two-port indicator did not go beyond the limits of the selected area of amplitude characteristic. On the other hand, the amplitude level of the AM signal envelope should significantly exceed the level of the AM signal.

the frequency and power of the harmonic of the greatest 50 amplitude of the parasitic envelope

level of polyharmonic working signal (Fig. 3). Level 1.21

 set to ensure that

further formation operations. AM signal with harmonic envelope g

with modulation depth m j, ((0.05-0.1),

and the voltage of the source is 8 constant

current - corresponding to the power level of the output signal of the modulator 2

frequency F arising due to the noise properties of the quadrupole. These requirements are fulfilled if the magnitude of m lies within 0.05., 1 After this, the amplitude of the AM signal V is measured with a selective voltmeter 6 at the frequency F, and the constant voltage is measured with the help of a constant voltmeter 5 this

13270232

and give the signal from the output of the modulator 2 on the studied quadrupole. The output signal of the quadrupole 3 is detected in amplitude using an amplitude detector 4, and then the DC voltage level is measured.

V of the detected signal (using a DC voltage voltmeter 5) and the voltage level Vp of a narrowband frequency component F - the detected signal (using a selective voltmeter g 6 /. Due to the nonideality of the segment voltmeter 6, it will measure the average level of the narrowband voltage) component in the frequency band P in the vicinity of the frequency F, which is taken into account when determining the noise parameters. The frequency F must lie within

lah 4 Fg

: f,

(where F.

ГР 1ms FY - absolute frequency instability of the generator; fpp is the smallest of the two values of F. ,,,, - f „f, F, P ,,„ the frequencies of the pass band of the quadripole are minimum and maximum, since if the left side of the inequality is violated

0 the selective voltmeter readings will be distorted by L1 -1kker noise of the generator 1 (Fig. 2), and if the right side of the inequality is violated, measurements will be carried out outside the passband of the four-port network being investigated.

Then, setting the frequency of the generator signal 7 to F, set its level to the corresponding depth

0 AM signal modulation at the quadrupole input, equal to fTig. At the same time, the depth of amplitude modulation m is chosen such that, in the process of changing the AM signal, the f-two-port network does not go beyond the limits of the selected portion of the amplitude characteristic. On the other hand, the amplitude level of the AM signal envelope should significantly exceed the amplitude of the parasitic envelope

frequency F arising due to the noise properties of the quadrupole. These requirements are satisfied if the value of m lies within 0.05., 1. After that, the amplitude of the AM signal V is measured at a frequency F using a selective voltmeter 6, and a constant voltage is measured using a constant-voltage voltmeter 5

the envelope component of the AM signal N /, after which the amplitude modulation depth t AM signal at the output of the quadrupole is determined,

m

H (v

 V / y For the considered

devices implementing the proposed method, the coefficient of is the shape factor of the detector characteristics of the amplitude detector (so, for a quadratic detector about 2).

Then the averages at two frequencies f j - F and f (, + F, the values of the parameters of the noise parameters are determined by the formulas:

with ff f - §K (f «.- F) + S (fo + F) KV O 2 - - -, R

(-) n

m

8if

, (f, p.). .y (f.:. F) tN ()

ikJnC - -) v c,

m

Bx

Then the described operations are repeated twice, setting the frequency of the generator

torus 7 is equal to -, and the frequency of the p gene

Rator 1 equal to fo- -5 first time

F

and fjj + -х- - second time, and by means of formulas (1) and (2) determine the average values of the specified noise parameters

respectively at frequencies fn o

and fjj and frequencies f and f + -r-After that, the magnitudes of the spectral density of the intensity and noise factor of the quadrupole, describing the quadrupole at the frequency fjj - F and the frequency are determined by the formulas:

2

S, {f, + F) S, (fo, F) + S, (

L). with (f. E.

About 1 0/1

 and 10 2 2

SK (fo- F) SK (fo, F) S. (fo4-; -) +

+ S (fo - 2

 2 2 (3)

N (fo + F) N (fo, F) + N (fo + | -; | -) - N (fo- - | -; - |);

1327023

4 N (fo-F) N (fo, F) -N (fo-f- | -; - | -) +

+ N (f, - -I-,). . C-)

F

formula of invention

. Q

15

20

25

thirty

40

Db

50

+

55

The method of measuring the spectral density of the noise intensity and noise ratio of the quadrupole, in accordance with which the quadrupole is exposed to an unmodulated signal, amplifies the narrow-band signal and measures its intensity, characterized in that, in order to increase the reliability of measurements of the specified parameters describing the quadrupole under the conditions of the impact of a polyharmonic operating signal on it with the amplitude of one of the harmonics outside the linear portion of the amplitude characteristic of the quadrupole ka, it is fed a harmonic signal with a power level Pj and a frequency f equal to the values of the power and frequency of the greatest harmonic of the input signal specified for the operating conditions, and the narrowband envelope frequency F of the quadrupole output signal in the 4 Fj.F range (where Fj. -. absolute instability of the frequency of the harmonic signal; - the smallest of the two values o and fo -, „„ and F «« Kc - is the minimum and maximum frequency of the quadrupole bandwidth and the constant component of the output signal of the quadripole and and their VP and / o levels are measured, then they are fed to a quadrupole amplitude-modulated signal with a harmonic envelope of frequency F and a known depth modulation rigjj and the modulation depth m is measured, the output signal of the four-pole network, then the average at two frequencies fj - F and F the values of the specified noise parameters are determined by the formulas:

S (f F) - .FL ± Jtikt.Q

(t,) -P N (,, p). Nif.: FLt.Nifo.tFU

Vf psx

2kT (mB ,,, jl

R is the input impedance of the quadrupole;

V-- is the level of the narrow-band envelope frequency F measured by the instrument with bandwidth P;

T is a constant Boltzmann and

the absolute temperature of the input resistance of the quadrupole;

et is the coefficient taking into account the amplitude distortion of the extracted narrow-band envelope frequency F, the indicated operations are repeated

times, changing the frequency F to F / 2,

S, (fo ± F) S (fo, F) t S (f, +) SK (fo- §-; - | -), N (f, ± F) N (f,, F) i N (f , + - | -; - | -) 5 S (f, - - | -; - | -).

the frequency is the first time

R

and at times, determined according to the indicated formulas. respectively, the values:

F f

with (f;: -. L) uif. ..)

 2 2 2 2

ten

and

S (f, -2-; -i -). N (fo - | -; - | -)

then, the spectral density of the noise intensity and noise ratio of the quadrupole, describing the quadrupole at a frequency of 5fj - F and a frequency f, are determined by the formulas:

1 (npttudnvostostno hbaonteoisikho Vfmt / - / rekhpolysniko

feL, .... |

I, rf.A

 I iptjt. g

Order 3384 / Al Circulation 730 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, st. Project, 4

,

|

I, rf.

  .... |

 I iptjt. g

Claims (2)

Claim A method for measuring the spectral density of noise intensity and the noise coefficient of a four-terminal network, according to which an unmodulated signal is applied to the four-terminal network under study, a narrow-band signal is extracted and its urov ^{15 is} measured, characterized in that, in order to increase the reliability of measurements of these parameters describing the four-terminal network under the influence of a polyharmonic working signal with the amplitude of one of the harmonics outside the linear section of the amplitude characteristic of four olyusnika, it is supplied harmonic signal urs ²⁵ therein power P _Bx and the frequency f ₆ equal specify to the operating conditions the values of power and frequency of the input signal is the highest harmonic, isolated narrowband envelope of the frequency F quadripole output signal in the range of 4 F _r <F ^<fpp ( ^g D ^e F _{f - the} absolute instability of the frequency of the harmonic signal; f _r p is the smallest of the two values of F _MaK with fo 35 and f ₀ - F _MMH and the minimum and maximum frequencies of the passband of the four-terminal network and the constant component of the envelope of the output signal of the four-terminal network and measure their ⁴⁰ levels V _F and V _o , then apply to the four-terminal amplitude -modulirovanny signal envelope harmonic frequency F and known depths modulation of t _Bx and measured modulation glubi45 well _vortices m quadripole output signal, after which the average on two frequencies f ₀ - F and F + f _p value of said noise parameters are determined by the odds Ulam: ⁵⁰ . sAi _t : .fLp ₆ ik * .El. ₌ ....... N _{(fo> F) =} Nif ._-_ FLt.Nlfo.iFl ₌ 2kT (br _Vias / r _Bx) ^£ P V'oi ² wherein R - input resistance of quadripole; Vp is the level of the narrow-band envelope of the frequency F, measured by a device with a passband P; k and T are the Boltzmann constant and the absolute temperature of the input resistance of the four-terminal network; b1 - coefficient taking into account the amplitude distortions of the allocated narrow-band envelope of frequency F, then these operations are repeated 15 two times, changing the frequency F to F / 2, and the frequency f to f ₀ - -z- - the first time F ^z and to f ₀ ⁺ ~ 2 ~ ~ the second time, determined by the indicated formulas, respectively, the values: s _k (f ₀ - 5-) ”N (f _p - 5-1-5-). Yu . 5 | A ⁺ ~ 2-> -r) .N (f ₀ 4- | -; - | -), after which the values of the spectral density of the noise intensity and the noise coefficient of the four-terminal network describing the four-terminal network at a frequency f ₀ - F and a frequency f ₀ + F, are determined by the formulas: S _k (f _a ± F) = S _K (f ₀ , F) t Sjf ₀ + - ”) l S _k (f ₀ -, N (f ₀ iF) = N (f ₀ , F) t N (f ₀ + S (f ₀ - - ^ -). fi »1 Rn-frequency At the output of the generator} I δ ¹ n ---- Γ. / 7 - / - / -..... on the 9th output of modulator 2 at the level of the generator? to the zero zero \ f \ r— / T «1 • X At the advantage of the modulator 2 with y / o no signal from the generator 7, it corresponds to a depth of XM0.1 Fie.Z