SU52845A1 - Multivibration wavemeter - Google Patents

Description

The invention relates to a multivibration wavemeter circuit that allows for very accurate wavelength measurements.

The following method is used for accurate wavelength (frequency) measurements:

1. After adding the measured frequency f with m to the harmonic of the reference

generator in the anode circuit of the detector lamp receive an intermediate frequency F, lying in a relatively narrow range of frequencies. Measurements in a given, usually very wide, frequency range are thus reduced to measuring frequencies in a narrow range. The required frequency is found by the formula:

L ™ 7s. (1)

where m is known in advance by calibrating the selector of the harmonics of the reference oscillator, and D is the frequency of the standard, which we take equal.

2. Frequency FJ. can, in turn, be presented as follows:

F n.WOOO ± F (2)

where “is the harmonic number of the multivibrator at 10 kHz synchronized from the reference oscillator and

the sound tone of the beat between the n harmonic of the multivibrator at 10 kHz and the frequency F.

3. A further task is to find F, n and determine the sign of the sonic tone. To obtain sv, the frequencies F and the nearest harmonic number of the multivibrator are detected at 10 kHz. Usually, for this purpose, the desired harmonic number is selected by the selector, having previously determined the frequency by a heterodyne wavemeter. At the same time, a complex selector and an accurate heterodyne wave meter are extremely expensive and cumbersome to make the entire frequency measurement setup.

The author proposes a fundamentally different method for determining F. In order to obtain a sound tone, the frequency F and not one any multivibrator harmonic, selected by the selector, but the whole frequency spectrum of the multivibrator is fed to the grid of the detector lamp.

If the grid circuit of the detector lamp is tuned to the frequency F, then for frequencies strongly differing from F. (for example, for the first harmonic numbers of the multivibrator), the resistance of the grid circuit is small and their amplitudes become comparable with the amplitudes of the higher harmonic numbers close in frequency to F. As a result of the detection of all these frequencies in the anode circuit of the detector, there are combination tones in Tc, among which there are two sound tones R. and 10,000 - P. The impedance of these sound frequencies will be significantly greater than the amplitude of all other combination tones. tones; therefore, the frequencies P. and 10,000 - / are easily and unmistakably determined by the zero beat method with a reference sound frequency.

To determine the number n, which must be substituted into formula (2) in the installation, an auxiliary crystal oscillator with two quartz frequencies is provided: kHz and / 1002 kHz.

A 10 kHz multivibrator must synchronize without any tuning from any of the frequencies f., F and f. At the same time synchronization of the multivibrator from the generator with a frequency of / or / corresponds to a relative detuning of it:

 / - / at / ET- / 2000 „.

6 - -f

J et

Consequently, when synchronizing a multivibrator from a generator with a frequency (its frequency decreases by Af 5). 10,000 Hz, where d / is the change in the fundamental frequency of the multivibrator in hertz, and 10,000 is the fundamental frequency in hertz. In our case, F

 2 10. 10,000 20 Hz.

When synchronized to / from, the main frequency of the multivibrator increases by AF 20Hz.

For the second harmonic number of the multivibrator, the absolute increase or decrease in frequency is already 40Hz. So l. 20Hz, where D / is the absolute frequency change of the i-th harmonic number of the multivibrator by 10 kHz.

If / 7jj is considered constant in the measurement process, the change in sound tone when the synchronization frequency changes from / „to / or / is equal to D /.

From here it is easy to find

(3)

20 20

the result being rounded to the nearest whole number. Here d / - - absolute

star

the value of the frequency difference P and /, „

Jbjb

(or) sound tone when synchronizing a multivibrator from a generator with a frequency of / (or /).

From the formula (3) it can be concluded that the sound tone must be determined with very high accuracy + (2-3) Hz over the entire range of sound frequencies. Otherwise, an error in determining the number of p.

If F is in the range

500 kHz 1000 kHz (4),

It is easy to prove that f, at selected frequencies / and /, lies within 1000 Hz cA / ig2000 Hz. You can increase the relative cut S, separated the frequency / and /. However, as we shall see below, such a measure will, however, allow the use of a rougher sound generator, but will increase the measurement area where it should be done to determine about three to three measurements of the sound tone. On the other hand, with the convergence of frequencies / and /, a sound generator is needed with such accuracy, which can only be achieved by greatly appreciating the entire installation. Note that to determine the sound tone, it is enough to have a graduated sound generator for the frequency range from 0 to 5000 Hz, since always one of two sound tones (F or 10,000 is in this range. If we assume an increase in the measurement error d /,

10 / J., The sound reference frequency generator range can be narrowed down to 500 - 5000 Hz. In this case, it is acceptable to use a sound generator with the generation of the fundamental frequency, which greatly simplifies its circuit.

To determine the harmonic number of the multivibrator and the f sign. provided

500 Hz f 4000 Hz (5)

(possible values of F. give a sound tone that satisfies condition (5)) proceed as follows. Get the sound tone F or zv sync multivibrator from f or from /. The synchronization frequency is chosen from the condition:

1500 Hz (or F ;;) 3000 HZ (b).

If conditions (5) and (b) are observed, F has the same sign as D / ST where - if the multivibrator is synchronized from the generator with a frequency of /, or - P of synchronization with a frequency of /. Number n is found by the formula (3).

In the accompanying drawings of FIG. 1 depicts a skeletal diagram of a multivibrational wavemeter; FIG. 2 shows the frequency chain that the multivibrator produces when synchronized with f of FIG. 3 is the same when synchronizing with the frequency /; FIG. 4 is a diagram of a selector with a distorter; FIG. 5-circuit selector with multivibrator; FIG. b - intermediate frequency detector; FIG. 7 - audio frequency detector; FIG. 8 is a diagram of an auxiliary generator for frequencies / and FIG. 9 is a diagram of the multivibration unit; FIG. 10 diagram of the beat indicator.

Suppose that the frequency generator found a frequency of 1263Hz. The value obtained satisfies condition (5). Synchronizing a multivibrator with a frequency of /, get an audio tone of / -gg. Suppose that it does not fit condition (b). Then synchronize the multivibrator with frequency /. A sound tone of 2460 Hz is obtained, from where the harmonic number of the multivibrator at 10 kHz is found.

) / 1263 - 2460

D 20

I

20

1197 °

(rounded to the nearest whole number). The sign of the sound frequency is determined: the difference - Fj has a minus sign, therefore F has also

minus. Therefore, F n. 10000 600000 -1263 598737 Hz.

The task of finding n and the sign of F is somewhat more complicated if condition (5) is not met, i.e., when less than 500 Hz or more than 4000 Hz. In this case, two values are obtained and it is impossible to determine which of them should be substituted into formula (3). For example, suppose that the frequency F is less than the frequency of the i-th harmonic number of the multivibrator, synchronized from / 3 by 200 Hz, i.e. F 200 Hz. FIG. 1 shows the frequency chain that the multivibrator provides. The dotted line shows the frequency F. When synchronizing a multivibrator from a generator, the frequency / frequency chain will shift, left and compressed, since the adjacent harmonic numbers will already be separated from each other not by 10,000 Hz, as before, but by 9980 Hz (Fig. 2) . The frequency F has not changed, the frequency of the “-th harmonic number has decreased, F has already turned to the right of n. Let us now assume 1500 Hz. It can be said that the absolute frequency of the harmonic number n has decreased by the value of sv + sv. . E. 1700 Hz, hence the formula (3)

DR

-20- 5 Let's conduct the same reasoning for the case when the frequency F is greater than the frequency n of the harmonic of the multivibrator (when synchronizing from f to 200 Hz). When switching to synchronization, the / frequency chain will shift to the left, i.e. the frequency of the harmonic decreases, the absolute decrease in the frequency of the nth harmonic is no longer equal to the sum of F and F, but the difference d / g 1500–200 1300 Hz and, trace 1300

- 65.

v20

In real conditions, the F sign is unknown. It must be determined. Therefore, it is impossible to say which 65 or 85 should be substituted into the formula (2). To determine the sign F and the number "

the third audio frequency is measured. Multivibrator synchronize frequency. The sound generator is a sound tone f. When choosing & f, consider two differences - / ;, and f -. The difference in magnitude is equal to the desired frequency, and, as before, has the same sign as i / s. These rules for determining n and the sign of F are also valid for F within 5000 / S 4000 Hz. For example, according to measurements F 316 Hz, 1915 Hz, g; 1684Hz. Consider two differences

/ 1916 - 116 1800 Hz sv - sv 116-1634 - 1568 Hz.

In absolute value, the first difference is greater; therefore AF

 1800 Hz and and 1 90; d / has 20 jb

plus sign; hence the f sign

also a plus. In this way

F p. / 33 900000 + 116 900116 Hz.

At frequencies. close to 5000 Hz, it is recommended to first determine the F sign, and then find the n. If the F sign is plus, then n is rounded to an integer, discarding the characters after the comma (when AF is divided by 20). If F is minus, n is rounded to the nearest whole number.

It is not always necessary to accurately determine all three frequencies f-, F., and. If it is clear from measurements that the difference between F and F. is less than 1000 Hz (by the condition of 1000 S d ss 2000 Hz), 4acTOTy; F. not precisely measured, but synchronizing the multivibrator from / and only finding P and F exactly,

The entire wavelength is in the form of an upright with a small table for the operator. The meter can be powered from both AC mains and batteries.

In the first case, a voltage regulator is required in the AC circuit or after rectification. When stabilizing with alternating current, a stabilization transformer can be applied using several factors at the same time that maintain a fixed voltage in the secondary circuit when the voltage of the network varies widely: magnetic saturation, variable dissipation, tuning the inductance of the secondary circuit to resonance with capacity and compensation winding. Such a transformer gives a voltage stability of about, which is sufficient even to power the anode and heat the reference oscillator. When stabilizing with alternating current, the load on the rectifier does not change, since during the operation of the multivibrator all elements of the circuit are switched on permanently. The choice of the design and circuit of the reference generator depends entirely on the requirements for its stability. When using quartz with a temperature coefficient

- 6 1.10 stability can be obtained

a quartz standard of the order of 2.10, even with the most primitive thermostat maintaining the temperature with an accuracy of 0.2 - 0.3 °. The quartz standard is compact and it is advisable to mount it in a wave meter rack along with synchronous clocks for frequency checking. With an increase in guaranteed stability, the dimensions of the reference generator grow. Standards are overgrown with a complex heating relay system, a signal relay, a voltage stabilizer, etc. Therefore, with a stability of 0.5 10 and above, the reference generator is best performed as a second autonomous rack.

Using the harmonic selector (Fig. 4), the required harmonic number of the reference oscillator is selected. A selector circuit (or a connected circuit with a small damping factor (included in the anode circuit of the distortion lamp. A large negative potential is given to the grid of this lamp and

large amplitude voltage from the reference generator. The lamp is placed in a mode of oscillation of the second kind with a small cut-off angle. The anode current is rich in higher harmonics that are selected by the selector. The selector is calibrated directly in the harmonic numbers. To select the amplitude of the harmonic, it is convenient to turn on the mixer in the grid circuit. Using one distorting lamp, set in the correct mode, it is possible to select harmonics up to 20-25 numbers with an amplitude sufficient for further detection. Another selector circuit with a multivibrator of 1 mHz is shown in FIG. 5. Multivibrator at 1 mHz synchronized from the reference oscillator on the main frequency. Voltage rich in harmonics is removed from the grid circuit of one of the lamps of the multivibrator. In the anode circuit of the separation lamp, operating in the amplification mode, include a selector. The multivibrator circuit has an advantage over the distortion lamp circuit in cases where the measurement range of the wavemeter increases towards higher frequencies and it becomes necessary to select harmonics with numbers 25-35.

It is recommended to install a dividing lamp on the grid of the intermediate-frequency detector lamp (Fig. B) and the harmonic of the reference oscillator and the frequency in order not to change the graduation of the selector when selecting the amplitude. Amplitude adjustment is made in the grid circuit of the lamp with the help of a shielded capacitor of small capacitance or induction-free potentiometer. In the anode circuit of the detector include a circuit that is tuned to a frequency of 500-1000kHz. The entire range is covered by turning the limb of the circuit capacitor. The scale of the capacitor — prostate — is graded in kilohertz. Graduation makes it easy to determine the harmonic number of the multivibrator. The scheme provides a cathode indicator, which set up the anode circuit at frequency F.

The frequency F allocated after detecting the frequencies ntf and / J. serves

on the sound detector grid. An audio frequency detector is also associated with a 10 kHz multivibrator (Fig. 7). The detector load is an ohmic resistance or a low frequency choke. It is advisable to turn on a low-frequency cutting filter with a cut-off frequency in the order of 5200-5300 Hz.

FIG. 8 shows a circuit diagram of an auxiliary generator according to the classical Pierce scheme. The switch and allows you to select the frequency for the synchronization / or /. It is convenient to have this switch in three positions like telephone jacks. Then, in one position of the jack handle, the auxiliary generator goes on frequency f and the multivibrator is synchronized on this frequency. In the second position, the multivibrator is synchronized with the frequency f, and the auxiliary generator is not used, finally, in the third position, the auxiliary generator goes in frequency / and synchronizes the multivibrator with itself. Trimmer capacitors Cj and c are used to adjust the frequencies / and / according to the beat indicator. The inclusion of small-capacity trimming capacitors parallel to quartz is quite common in oscillation circuits, where a change in the oscillator frequency small by 20–30 Hz is required. It is desirable to have quartz Qi Qg with a low temperature coefficient. It is advisable to use a thermostat, since the frequency during measurements is corrected by a reference generator, and the measurement time itself is small.

A 10 kHz multivibrator cannot be synchronized with the frequencies / d, /, and

/ directly, therefore, a frequency division step is introduced. As such a divider using a 100 kHz multivibrator. The scheme of the multivibration unit is shown in FIG. 9. Through a dividing lamp, a synchronizing frequency is fed to the anode circuit of the multivibrator at 100 kHz. With proper selection of the amplitude of synchronization and parameters

Circuit multivibrator will be keen on the tenth harmonic. The frequency of 100 kHz is removed from the multivibrator, which is separated from the harmonics in the purifier by the anode circuit of the dividing lamp. The frequency of 100 kHz, in turn, synchronizes the multivibrator to 10 kHz, also in the tenth harmonic. Through a second separation lamp, the multivibrator is connected to an audio frequency detector.

The 1 kHz multivibrator is designed to correct the graduation of the sound generator, to correct the frequencies / and / in frequency / 3, and to check the reference oscillator with the help of synchronous clocks using time signals. This multivibrator is synchronized with a frequency of 10 kHz over the tenth harmonic.

Beat indicator grid (Fig. 10) is fed through the dividing lamps L and JIz to the grid of the detector lamp 3 and / or /, depending on the position of the switch / 7 (Fig. 8). The detector lamp grid is also linked to an IkHz multivibrator. A galvanometer in the anode circuit registers combinational zero beats, as a result of the addition of frequencies f, to / or / to the second harmonic of the multivibrator on IkHz. The beat indicator is included for the entire time of working with the wave meter. The slow movement of the galvanometer needle will serve as proof that the auxiliary generator has frequencies that differ from / exactly by 2000 Hz.

As indicated, the sound generator should have a range of O - 5000 Hz. By reducing accuracy

measurements on D / 30% of possible values of frequency the range of the sound generator can be narrowed to 500-5000 Hz. In order to obtain a high graduation rate, the sound generator is assembled according to a scheme with parametric stabilization, and the loops of the local oscillators are performed with a minimum temperature coefficient. Sound generator must have good mechanical strength.

When using circuits on beats in a sound generator, it is recommended to choose the frequencies of the local oscillators in the range of 60-40 kHz, to use a large constant capacitance in the circuits and to take a capacitive variable capacitor. Such a capacitor in this case gives an almost linear dependence between the sound frequency and the scale divisions. The entire range (O - 5000 Hz) is best divided into 2-3 sub-ranges to improve the accuracy of the reference. Together with the sound generator, the zero-beat indicator is mounted. The circuit is similar to the diagram in FIG. 10. The indicator is used to adjust the calibration of the sound generator and to determine the zero beat frequencies F, F, and. Zero beats fix the pair; visually - by oscillations of the hand of a galvanometer and to the telephone - by a characteristic increase and decrease in volume. The sound generator, in addition to the calibration curves, must have a table of discrete points of multiples of 1000 Hz for correction (five points are enough). When using a multivibration wavemeter to measure frequencies over the air, a receiver is added to the installation for the measurement range and a stable oscillator with a smooth tuning.

Measurement order. 1. The harmbnik is selected by setting the dial to the appropriate division, the desired harmonic number t of the reference oscillator, so that as a result of the addition of the frequencies mf and /, the condition 500 kHz / S31000 kHz is met.

2. On the cathode indicator, adjust the intermediate frequency circuit to resonance with F.

3. Multivibrator at 10 kHz synchronized frequency f. Verify the calibration of the sound generator. An acoustic tone F, is determined from the sound generator.

4. According to the beat indicator, the auxiliary generator is tuned exactly to the frequencies / 998 kHz and / 1002 kHz. If F satisfies the condition 500 f sv 4000 Hz, the frequency

synchronization is chosen so that the condition is also satisfied, (or /; j e3000 HZ. The sound tone F or FJ is determined by the sound generator. The definition and / has already been disassembled.

If the condition is not observed (5), all three sound tones F are measured.

F and Y were noted, it is not always necessary to accurately determine all three frequencies.

When measuring the frequencies of radio stations, a pre-stable generator with a smooth tuning is tuned to the receiving station with possible accuracy. The frequency of a stable oscillator is measured with a multivibration wavemeter.

When measuring frequency / should be known in advance with an accuracy of 500-800 kHz.

The subject matter of the invention.

A multivibration wave meter using combination beats of several harmonics of a multivibrator with a definable frequency, lowered addition with its reference harmonic, characterized in that to determine the harmonic number of the multivibrator, the change in the sound tone by detuning the synchronizing frequency is used. to the author's testimony of Yu. V. No. 52845 Bogoslovsky