SU1228036A1 - Apparatus for measuring non-linear distortions in generators of frequency-modulated signals - Google Patents

Abstract

The invention relates to a radio metering technique, may be used in measurement generators, and is additional to auth. No. 1026074. The purpose of the invention is to increase the resolution of the measurement of nonlinear distortion at and - Ge high modulating frequencies. The device contains the sources 1 and 10 of the modulating signal, the tested generator 2 FM signals, superhetero. Dinny receiver 3 FM signals, including a mixer 4 with tunable local oscillator 5, an amplifier 6 intermediate frequency with amplitude limiter and frequency detector 7. In addition, the device contains an adjustable non-linear functional converter 8, a spectrum analyzer 9, FM-local oscillator 11 and a mixer 12. The introduction of the source 10 of the modulating signal, the FM local oscillator And, the mixer 12 and their connection with the elements of the device provided the ability to compensate for their own nonlinear distortion of the superheterodyne receiver, as and odd harmonics. 2 Il. i (C

Description

low level of nonlinear distortion. At the output of the tested generator 2, the modulation law distorts and contains harmonics 2i ,, 357,, р (where

p 1,2,3 ... integer) modulating frequency L

s

. + “SchrSp,), l

 one

The invention relates to a radio-measuring technique and is intended for accurate and precise measurements of non-linear distortions of modulating voltage in frequency-modulated (FM) generators for various purposes, in particular, in measuring generators used in various areas radio engineering, metrology and testing practice.

The purpose of the invention is to increase the resolution of measuring nonlinear distortions in FM signal generators at high modulating frequencies.

Figure 1 shows the block diagram of the device; figure 2 - spectrogram of the signal at the input of the analyzer IcneKTpa.20

A device for measuring nonlinear (i UjCOS HdKaxeHidi in FM signal generators contains a source of I modulating where, is the carrier frequency of the local oscillator; the signal that is actually tested by the GoA signal) q-th harmonic deviation (q 1,2,3. ..) modularity

 where and,, OW are, respectively, the amplitude and carrier frequency of the signal of the generator being checked;

4Wp (n,) is the deviation of the p -th harmonics of the modulating frequency I ,.

FM local oscillator 11 is modulated by a sinusoidal voltage of frequency P from source 10, the modulation law of the signal at the output of the local oscillator 11 is also distorted and looks like

g +00

L v

ISOS ,, (Pg)

year

 P

g, (2)

Ramper of 2 FM signals, superheterodyne receiver of 3 FM signals, containing mixer 4 with tunable local oscillator 5, intermediate frequency amplifier with amplitude limiter 6, frequency detector 7, adjustable non-linear functional converter 8, spectrum analyzer 9, second modulating source 10, FM —Heterodyne 11 and mixer 12. The first input of the mixer 12 is connected in series with the first source 1 of the modulating signal and the tested generator 2 of the FM signals to the second input of the mixer 12 connected 30

35

Sj frequencies.

The signal of the total carrier frequency 1 (s principle for measuring can be used and the signal of the difference frequency COo-w,) at the output of the mixer 12 has a two-tone law of frequency modulation:

U, W.U3CoJco: br-5inp ", i.

L

 )

V

those.

p.1

g

pn, sJnciSlii,

(3)

the modulation law contains

are connected in series the second component of the first (p q 1) and the source of the modulating signal 10 and the highest harmonics of the modulating frequencies

FM local oscillator 11. To the output of mixer 12 a superheterodyne receiver of 3 FM signals is connected, consisting of a serially connected mixer 4 with a tunable local oscillator 5, an intermediate frequency amplifier with an amplitude limiter. 6 and the frequency detector 7. To the output of the superheterodin45

L, Ia. A superheterodyne receiver 3 is tuned to the sum signal (3).

When the signal (3) passes through the mixer 4, the intermediate frequency amplifier 6 with the limiter and the frequent detector 7 of the superheterodyne receiver 3 due to its own non-linear receiver 3 FM signals of the subsequent distortion of the frequency path

An adjustable nonlinear functional converter 8 and a spectrum analyzer 9 are connected.

The device works in the same way.

On checking the generator 2 FM signals, a sinusoidal modulating voltage is applied with a frequency Si and

12280362

low level of nonlinear distortion. At the output of the tested generator 2, the modulation law distorts and contains harmonics 2i ,, 357,, р (where

p 1,2,3 ... integer) modulating frequency L

 u (ibUj-cos fO

s

. + “SchrSp,), l

 one

 u (ibUj-cos

 where and,, OW are, respectively, the amplitude and carrier frequency of the signal of the generator being checked;

4Wp (n,) is the deviation of the p -th harmonics of the modulating frequency I ,.

FM local oscillator 11 is modulated by a sinusoidal voltage of frequency P from source 10, the law of modulation of the signal at the output of the local oscillator 11 is also distorted and looks like

carrier frequency of the local oscillator; ) deviatsi q-th garmo 1,2,3 ...) modular

g +00

L v

ISOS ,, (Pg)

year

 P

g, (2)

Sj frequencies.

The signal of the total carrier frequency 1 (s principle for measuring can be used and the signal of the difference frequency COo-w,) at the output of the mixer 12 has a two-tone law of frequency modulation:

U, W.U3CoJco: br-5inp ", i.

L

 )

V

those.

p.1

g

pn, sJnciSlii,

(3)

the modulation law contains

45

L, Ia. A superheterodyne receiver 3 is tuned to the sum frequency signal (3).

With the passage of the signal (3) through the mixer 4, the amplifier 6 intermediate frequency with the limiter and the frequency detector 7 superheterodyne receiver 3 due to its own noise 55

the detec- tion in the signal (3) adds a new composition to the Cie. Moreover, due to the presence of a two-tone signal with non-linearity of the frequency detection path, both harmonics of the modulating frequencies and combination components of the form p L, i q52 arise. With this in mind, for the voltage

the output of frequency detector 7 with a slope S can be written

 00

ZIucOp (Q, 1co5pn, D. (02 p 1

4-00

 Co5aOii + Z i (Op (f2, lcoq (pni +) ift "tg

+ 00

400 + OP

P ioJCO Vosl t4 2: dso q, 2 p.i cjci

x (, ± C nj co5 {pn, ± (2jHl. (4)

In expression (4), the third and fourth terms in square brackets characterize the harmonics modulating the frequencies arising in the superheterodyne receiver 3, and each of the harmonics has an arbitrary phase shift cfp and a court with respect to the corresponding harmonic of the checked FM generator (the first and second terms in square brackets of formula (4) i and vectorially summed with it. Therefore, signal (4) can be written

as

I ,,

G + OO

I4Sh 5 gr dso p (ALS05 (rp, + Cf pH t

4-00

And (a ((({c;.,

+ OO c-OO-1

+ 11 And yO (rp,) so5 (rL,) Y, ri I- (5)

where Гр and Г- are the weighting factors taking into account the summation taking into account the phases of the harmonics of the frequencies I and Q arising in the tested generator 2 and the superheterodyne receiver 3.

The spectrogram of the signal (5) at the output of the frequency detector 7, taking into account the harmonics and the combination frequencies up to the third order, is shown in step 4. The dotted line in Fig. 2 outlines the components in which the non-linear distortion information of the tested generator 2 is enclosed.

Direct measurement of nonlinear distortions as the relative amplitudes of the second and third harmonics of the modulating frequency at the output of the frequency detector 7 is impossible, since the second and third harmonics were formed as a result of the vector summation of the harmonics of the tested generator 2 and the super heterodyne receiver 3. However, due to the

combination components I, + P 2L, n I, 2fZ, + fZ, etc., arising only in the superheterodyne receiver 3 and carrying full information about its 5 own nonlinear distortions, it is possible to accurately measure the amplitudes of the harmonics of the modulating frequency p , arising in the checked generator. It is known that with appropriate

10 the choice of the modulation frequency 52, and P in the dual tone FM signal, there is a one-to-one relationship between the level of the amplitudes of the combinational components and the level of the harmonic components

5 when the signal passes through a distorting circuit. A similar connection exists for the case of passing the sum of two harmonic oscillations through a non-linear circuit. Consequently,

0 if the signals (5) are passed through an adjustable nonlinear functional converter 8, with which the analyzer 9 compensates for the combination components of the second (P, + U) or third (2P, + 2 or S7, -) order, then it can be argued that the own non-linear distortions of the superheterodyne receiver 3 are also compensated, i.e.

Q the third and fourth terms in formula (4) disappear. This allows accurate measurement of the distortion in the checked generator and with high resolution.

5 Measurements using the device are carried out as follows.

The adjustable nonlinear fuction converter 8 is set to the linear conversion mode and a spectrogram is observed on the screen of the spectrum analyzer 9 (Fig. 2). After that, by adjusting the nonlinear characteristic of the converter 8, the reduction tf of the disappearance 5 of the response of the second-order combinational component I, SZj is achieved corresponds to the full compensation of the own harmonic distortion of the superheterodyne receiver in the second harmonic. The spectral analyzer measures the second harmonic level of the modulating frequency SI ,. Then, by adjusting the nonlinear characteristic of the converter 8, the response of the third-order combinational component of the third order of 2π is obtained, - L or L, and the third harmonic level of the modulating frequency is measured. According to the results of the harmonic level measurements, the nonlinear distortion coefficient of the generator being tested is determined.

Due to the introduction of a second source of modulating signal, FM local oscillator and mixer into the device, it is possible to compensate for the own nonlinear distortion of the superheterodyne receiver in both even and odd harmonics.

Claims (1)

Invention Formula Device for measuring nonlinear distortion in generators frequency editor L. Pchelinska Compiled by E. Minkin Tehred, G.Gerber Proofreader E.Sirohman Order 2284/46 Circulation 728 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, Projecto st., 4 modulated signals on av.sv. No. 1026074, characterized in that, in order to increase the resolution of measuring nonlinear distortions at high modulating frequencies, a second source of modulating signal is additionally introduced into it la, the frequency-modulated local oscillator and mixer, the output of which is connected to the input of the superheterodyne receiver of frequency-modulated signals, and the second input of the input The mixer is connected to the output of a test generator of frequency modulated signals.