SU1033991A1 - Four-terminal network noise factor measuring device - Google Patents

Abstract

. THE DEVICE FOR MEASURING THE RATE OF NOISE OF THE CHBTYREKPOLUSNIK, provides a reference noise source, an amplifier, an output connected to the input of a quadratic voltmeter, and a switch that, in order to improve accuracy. measurements, it introduced an attenuator, two capacitors, a second switch and a noise generator, and a reference one. the noise source is made in the form of two series-connected resistors, while the amplifier input is connected to one of the resistor terminals and to the output of the first capacitor, the second output of which is connected to the moving contact of the first switch, the first fixed contact of which is connected to the device body, the second fixed contact - with the first fixed contact of the second switch and with the output point of the resistors, the second output of the second resistor, which is connected to the device body, and the third fixed contact - with the first input terminal of the device, the second input terminal of which through an attenuator is connected with “i second fixed contact of the second. W j switch, movable contact; The second capacitor is connected to the output of the noise generator. co T co a co co f S / / g // nn //. t

Description

The invention relates to a radio measuring technique and can be used to measure the noise factor of quadrupoles. A device for measuring the noise factor is known by measuring the output power of the noise at the output of the test device with the generator turned on and off using the method of doubling the power at the output of the test device using a calibration-. attenuator and indicator 1 The disadvantage of this device is the low accuracy of measurements due to the need to calibrate the noise generator by the output power and, due to the calibration error of the attenuator directly included in the measurement result. Closest to the present invention is a noise figure measurement device comprising a reference noise source, an amplifier, a quadratic voltmeter, a switch, and a reactive element used as the input resistance of a quadrupole 2 under test. The amplifier with an input calibration resistor is connected to the output quadrature voltmeter. Based on thermal noise resistance, a quadratic voltmeter indicator is calibrated. A disadvantage of the known device is the low accuracy of measurement, as well as the self-noise of the amplifiers is soy, measurable with the calibration noise and the noise of the device under test. Therefore, it is necessary to have as large a signal as possible with the calibration noise resistors, which is ensured by their large value at a given frequency band and temperature. However, the calibration resistors shunt the input resistance of the amplifier, which is practically limited to its active and reactive components. The use of a sampling capacitor at the input of the device under test to compensate for the reactive component, 1 of the resistance at the measurement frequency, makes it impossible to accurately set the magnitude of the signal source even at relatively narrow frequency bands of the signal to be tracked, which limits the use of this device to very narrow-band measurements, especially in the low frequency range. The purpose of the invention is to improve the accuracy of measurements. This goal is achieved by the fact that a quadrupole noise figure measuring device, containing a reference noise source, an amplifier, an output connected to a quadratic voltmeter input, and a switch, an attenuator, two capacitors, a second switch, and a generator are entered. noise, and the reference noise source is made in the form of two series-connected resistors, while the amplifier input is connected to one of the terminals of the resistor and to the output of the first capacitor, the second in whose iodine is connected to the moving contact of the first switch, the first fixed contact of which is connected to the device body, the second fixed contact to the first fixed contact of the second switch and the output point of resistors, the second output of the second resistor from which is connected to the device body, and the third fixed contact from the first input terminal of the device; the second input terminal of which through an attenuator is connected to the second fixed contact of the second switch, the movable contact of which is , the second capacitor cut is connected to the | output of the noise generator. - Ya drawing is called a block diagram of the device. The device contains an amplifier 1, a quadratic band voltmeter 2, a reference noise source 3, a full voltage in the form of two series-connected resistors 4 and 5, the first, switch b, quadrupole test 7, noise generator 8, second switch 9, attenuator 10 and input terminals 11 and 12. The capacitors 13 and 14 are designed to separate the circuits by DC. Before the start of work, the device is calibrated, the purpose of which is to determine the intrinsic noise of the amplifier, to check the input resistance of the amplifier and to calibrate it. noise cue. First, switches b and 9 are set to position and the input of the amplifier is closed with a variable signal through capacitor 13 to the case. A quadratic voltmeter measures the intrinsic noise of an amplifier and the noise of a voltmeter. At the same time, the own noise of the amplifier and the voltmeter can be compensated by any known method. Therefore, we can assume that, in this case, the quadratic voltmeter is set to a zero value, Yaatem trans-. switch 6 is switched to the position of the reference amplifier at the input of the amplifier; its average effective value is determined by the formula Ujug lf4ia (RlTR5T, |. where 4. is the average effective value of the noise voltage; k is the Boltzmann constant (k 1,3 1.3181102 / to),

T is the absolute temperature of this: a single source of noise; (Rft-Ri) - the total value of the resistances of series-connected resistors 4 and 5 of the reference noise source L - the noise band is effective. The input of the amplifier is supplied with a voltage determined by the division factor consisting of the input resistance of the amplifier Rj and the internal resistance of the reference noise source equal to R.j + Rj: O.g, ex. ex ВХ1 ШЭ1 R + R1 + R2 I (RH-R2),, is the average effective knowledge of the voltage of the reference noise source, input to the amplifier R., is the input resistance Ol-. bodies for noise signals A quadratic voltmeter in this case will measure the value defined by the formula. .1-ТЙГГ2 / Sx у (КИ-К2), .RlH.R2 /, tde Р1 - reading of a quadratic voltmeter; I Ku - gain factor. . Then switch b to switch to position c. At the same time resisto. shunted by capacitance 13, for example, noise of the reference noise is determined only by the noise of the resistor 4 52L y41cT fRli VU2 RBX (in 2 4ftTflfR-1, i

de Uiu32- the average effective voltage of the noise signal generated by the resistor 4

 reference noise source;

8X2. the effective voltage value of the noise of the resistor of the torus 4 of the reference noise source supplied to: the input of the amplifier;

P2 - quadratic reading

voltmeter 65

The ratio of the readings of the quadratic; voltmeter in the case of x 5 and in will be

41 (Tdf (RH-R2;

one.

G4 P2

WU Y R-1 + R Rg -f-R1 + R2 / R4

pz (41cTgJfR U Jk,

Rde Kug, is the gain of the systems with a measured quadrupole.

Switch 9 is then moved to position 8. At the same time, the input of the attenuator 10, which is intended for the output generator resistance mode, is connected to the output of the generator 8. The signal R for the measured four, the value of N is determined only by the values of the resistance of the reference noise source R1 and R2 and the input resistance of the amplifier Rgy. Therefore, by controlling the value of N, it is possible to control the value of the input impedance of the amplifier with selected values of R1 and R2 and, if necessary, adjust it. . Thus, the effect of the input impedance of the amplifier is taken into account when calibrating the reference noise source. Then switch 9 is turned to position 5. By setting the change in the output voltage of the noise generator to the readings of a quadratic voltmeter again equal to P1, we get a signal to. The input of the amplifier is equal. . In this case, the calibrated generator is calibrated, based on the thermal noise of the reference noise source, taking into account its shunting by the input impedance of the amplifier. This is where the calibration of the device ends. The process of measuring the noise figure follows this way. Switch 6 Shift c. position about. , while the reference noise source 3, together with the input impedance of the amplifier, represents the load for the measured quadrupole. Set the mode of the quadrupole DC. Then, the s position and the switch 9, read the P 3 of a quadratic voltmeter, which is determined by the combined action of the thermal noise of the output impedance of the signal generator R54 and the intrinsic noise Ujj, measured by a four-terminal network. The voltmeter reading will be proporidonal. . to the square of their loads; rehpoljusnika and attenuation of the output signal of the calibrated noise level generator 8 (corresponding to the thermal noise of the output impedance of the signal generator for the measured quadrupole. The value R .. is specified in the documentation for a specific type of quadrupole. In this case, the division ratio of the calibrated attenuator 10 can be defined as .. (YI-YA2) Le Q Q IR-H-RZ. The value of Eg ,,, is assumed to be equal Ugx,; /, which is provided in the process of previously performed calibration of the device. Thus, the resistor is connected to the voltage of the thermal noise. .dobavl is precisely essentially the same magnitude, i.e. at the input quadripole have, a signal generator with an output resistance R, cos giving noise signal equivalent thermal noise resistance greatness .noy2k. indications R 4 will have a quadratic voltmeter vidg..

P4 (41cr4f-ZR +02

KT-J.

The noise figure can be calculated; from the following relation: 35

R / R

Р Р с. / Ш

- with (AND OUT

R

 Р Р

/ RSH

UI from OUT

OUT

svyh

-coefficient noise). ., 40

-power input signal. measuring instrument;

-power noise at the entrance; . measuring instrument.

It is seen from the fyms of the emulsion that the values included in it contain the values of РЗ and Р4 of a quadratic voltmeter. As a result, a direct reading of the value (the coefficient and the noise of the measured quadrupole is made according to two measurements of RZ and P4 of a quad voltmeter, the scale is calibrated to goatly. According to the formula

. p4-rz |

The noise factor measurement error is 0.25 dB, Pg is the signal output power. the device being measured P g is the noise power at the output of the device being measured. In the case under consideration, the signal powers P and the noise PcJ at the input are equal; they correspond to the value 4NDC; output signal power -. D-1) 1 -DYD corresponds to a value of 41a, pd to Gain 1 of the power source, the power-noise output Pjygj, is determined by the value (4 T / 3fRc.- -g, c) KT. Substituting these values into the noise figure formula, we have: After the conversion, we get:) (41cT; jf (4CTL R;, + Oy J 4KTdfRj. (4tcraf) - (41cT4 RC Oj) (41tT R 02) k, (41cT4f ,, - (4fcT4fR - OyK

Claims (1)

. DEVICE FOR MEASURING THE FOUR-POLE NOISE COEFFICIENT, containing a reference noise source, an amplifier connected to the input of a quadratic voltmeter with an output, and a switch, with the aim of increasing accuracy. measurements, an attenuator, two capacitors, a second switch and a noise generator are introduced into it, and a reference one. the noise source is made in the form of two. series-connected resisto. ditch, while the input of the amplifier is connected to one of the terminals of the resistor and to the terminal of the first capacitor, the second terminal of which is connected to the movable contact of the first switch, the first fixed contact of which is connected to the device body, the second stationary contact to the first stationary contact of the second switch and tori, the second one of which devices, and the beat - with the first input terminal of the device, the second input terminal of which _ through the attenuator is connected to <g, the second fixed contact of the second. | a switch whose movable contact is ^ (through the second capacitor 4 m is connected to the output of the noise generator. vj. with the output point, the resistive output of the second is resistively connected to the housing · third fixed cong 1Q33991