Circuit quartz oscillator on a transistor 465 kHz. Universal probe generator

Universal generator-probe

Compact test signal generators are very popular among radio amateurs; they are useful for testing and setting up radio receiving and sound reproducing equipment. We offer another design of a similar generator, characterized by an expanded set of fixed frequencies.

Industrial and homemade radio receiving equipment contains 3Ch and IF paths, and the IF frequencies have different meanings: 455 kHz - in imported and 465 kHz in domestic AM signal receivers; 5.5, 6.5 and 10.7 MHz - in FM signal receivers. The magazine "Radio" has already published circuits of generator-probes for testing 3Ch and IF paths. As a rule, they produce two signals - 3F and a modulated IF signal with one of the named frequencies. To avoid having to make several probes, the proposed generator provides frequency switching. It is suitable for testing almost any equipment, including the audio path of televisions.

The generator-probe circuit is shown in Fig. 1.

The audio frequency generator is assembled on transistor VT1 according to a circuit with a phase-shifting RC circuit (capacitors C1 - C4 and resistors R1 - R3). The emitter follower on transistor VT2 decouples the generator from the load - the RF generator. The latter is made on transistor VT3. Instead of resonant LC circuits, the generator uses small-sized piezoceramic IF filters ZQ1 - ZQ5 from radios or televisions. The filter corresponding to the desired IF is selected by switches SA1 (FM or AM) and SA2 (specific IF value). In the 3H position, no filter is turned on and the RF generator does not work. In this case, only the 3H signal is output.

The modulated RF signal is supplied to the output emitter follower, assembled on a VT4 transistor, which significantly weakens the influence of the load (the units being tested) on the RF and 3F generators. Variable resistor R8 sets the required output signal level. Separating capacitors C7 and C8 at the generator output are switched by button SB1. In the position of switch SB1 shown in the diagram, only modulated RF signals pass through capacitor C7 of a relatively small capacitance. When switches SA1 and SA2 are set to position “34”, use button SB1 to connect high-capacity capacitor C8. Power is supplied to the probe from the power circuits of the equipment being tested. The supply voltage can range from 3 to 12 V.

The generator-probe is assembled on a board made of getinax or fiberglass. The location of parts and connecting conductors are shown in Fig. 2. If the board is made of foil material, then a printed circuit board can be made according to the drawing. After manufacturing, the board is placed in any suitable housing, for example, from the GSP-1 grid field generator.

(click to enlarge)

Transistors VT1 - VT4 can be replaced with KT3102 or KT312 with any letter index; it is advisable to select transistors VT2 and VT3 with the highest current transfer coefficient. Any piezoceramic filters from domestic or imported equipment with suitable frequencies are suitable for the HF generator.

Switch SA1 is used type PD9-1, SA2 - PD21-2, button SB1 - MP-7 or other small-sized. All resistors are MLT-0.125 (you can use MLT-0.25), capacitors are KD, KM, K10 or other small ones. Resistor R8 - SPO-0.15 or SP-3-386. The output contact X1 is a needle soldered to a pad on the board (on the right in Fig. 2), and contact X2 is a wire with an alligator clip soldered at the end.

Setting up the probe generator begins with setting the mode of transistor VT1. Its collector voltage should be 1.5 V with a supply voltage of 3 V. To set the collector voltage, resistor R4 is selected. After this, the presence of generation is checked when the supply voltage changes from 3 to 12 V. Then capacitor C3 is unsoldered (the 3Ch generator stops working), a supply voltage of 3 V is applied and by selecting resistor R7, RF generation occurs at all fixed frequencies, i.e. when connecting any piezoceramic filter. If generation does not occur in any of the positions of switches SA1 and SA2 (most often this happens in position “10.7”), select resistor R6 and then again check the operation of the HF generator at all frequencies.

You can verify the presence of RF generation by connecting a high-frequency oscilloscope, millivoltmeter, a simple detector with a measuring head, or a frequency meter to the probe output. In the latter case, the generation frequency is also checked. Then install capacitor C3 in place and, if you have an oscilloscope, check the quality of the RF signal modulation.

Working with the probe is simple. If a 3H amplifier is being tested, switches SA1 and SA2 are set to the “3H” position, press the SB1 button and apply the 3H signal with probe X1 alternately to the various stages of the amplifier being tested, not forgetting to set the required signal level with resistor R8. When checking the amplifier of various equipment, select the required frequency value using switches SA1 and SA2; do not press the SB1 button. By applying a signal to the input of the amplifier, first after the main selection filter, and then before it, one is convinced that the signal passes through the filter and the amplifier. Otherwise, the UPC is checked step by step.

Literature

1. Malinovsky D. Frequency synthesizer for the 144 MHz range. - Radio, 1990, No. 5, p. 25.
2. Titov A. Probe-generator for testing radio receivers. - Radio, 1990, No. 10, p. 82.83.
3. Nechaev I. Probe-generator for testing radio equipment. - Radio, 2000, No. 8, p. 57.

The most commonly used measuring generator in the circle is the GSS - a standard signal generator, which, producing electrical frequency oscillations from several hertz to tens and hundreds of megahertz, can be a source of amplitude-modulated signals that simulate signals from broadcasting stations. In addition to the industrial generator, the circle also uses homemade simple measuring generators. Their construction is an integral part of the activities of radio engineering clubs in the 1st and 2nd years of classes.

Single-transistor oscillation generator 3H, the diagram of which is shown in Fig. 60 may become the first amateur radio measuring generator. The device produces sinusoidal oscillations at a frequency of 1 kHz. A signal of this frequency is most often used to test amplifiers 34, audio frequency paths of broadcast receivers.

The generator consists of a single-stage amplifier on transistor V and a double T-filter connected between the collector and the base of the transistor. Such electrical filters are called T-shaped, because the circuit design of their elements resembles the letter T. In the generator circuit, one such filter is formed by resistors R2, R4 and capacitor C2t, the second is formed by capacitors C/, SZ and resistor R3. They are connected to each other in parallel and form a positive feedback between the collector and the base of the transistor, due to which the amplifier is excited and becomes an oscillator of a fixed frequency. The frequency of the generated oscillations is determined by the values ​​of the capacitors and resistors forming a double T filter. From resistor R5y, which is the load of the transistor, oscillations of the generator are supplied through capacitor C4 to variable resistor R7, and from it to the input of the tested amplifier 34. With this resistor, the voltage at the output of the generator can be smoothly varied from zero to 1.5...2 V.

Resistors R4 and R2, included in the double T-filter, together with resistor R1 form a voltage amplifier, from which a negative bias voltage is applied to the base of the transistor. Resistor R6 improves the shape of the generated oscillations.

To check whether the generator is working, just connect headphones to its output - a medium-pitched sound will appear in them, changing in volume as you rotate the variable resistor R7 knob.

The GT308V transistor can be replaced with a P416B or another germanium high-frequency transistor with a static current transfer coefficient of at least 80. Variable resistor R7 type SP-1, resistors R1—R5—ML T-0.125 or MLT-0.25, resistor R6—TVO-0.125 (there are no MLT type resistors with a nominal resistance of about 5 Ohms). The power source for the generator can be a Krona battery or two connected 3336L batteries.

Measuring generator(Developed by B. Stepanov, Moscow), generating sinusoidal oscillations of a fixed frequency of 1 kHz, can be assembled on a K122UN1B microcircuit (Fig. 61). The output voltage of the generator at a load with a resistance of 10 kOhm is about 2 V.

The amplifier of the microcircuit is self-excited due to the inclusion between its output (pin I) and input (pin 4) of a phase-shifting RC circuit formed by capacitors C1 - C3, resistors R1 - R5 and input impedance the first transistor of the microcircuit. The frequency of the generated oscillations can be changed within a wide range by replacing capacitors C1-C3 with capacitors of other capacities, but always of the same nominal value. As the capacitance of these capacitors decreases, the frequency of the generated oscillations increases, and vice versa. The resistances of resistors R3 and R5, selected when setting up the generator, can be in the range of 1.5...4.7 kOhm. Electrolytic capacitor C4 eliminates negative feedback alternating current, acting between the transistors of the microcircuit.

The output voltage and harmonic distortion depend on the depth of the positive feedback, set by trimming resistor R4 during tuning of the generator. First, the chain of resistors R3-R5 is replaced with a variable resistor with a resistance of 10 kOhm. The signal from the generator output is fed to the “Y” input of the oscilloscope and, monitoring its image on the screen, empirically find a position for the variable resistor motor at which the oscillations stop. Then the resistance of both arms of the variable resistor is measured, the connection of the tuning resistor R4 is restored, resistor R3 is included in the chain with a nominal resistance close to the resistance of the upper arm (from the upper terminal to the engine), and resistor R5 with a resistance equal to the resistance of the lower arm of the variable resistor.

After this, the tuning resistor R4 sets the optimal feedback depth, at which the oscillation amplitude will be greatest and without distortion.

In the event that strict requirements are not imposed on the shape of the output signal, that is, they do not pay attention to some distortions, then the chain of resistors R3-R5 can be eliminated altogether by connecting the right (according to the diagram) terminal of capacitor C3 directly to terminal 11 of the microcircuit.

In the generator, instead of the K122UN1B microcircuit, you can use other microcircuits of this series or similar microcircuits of the K118 series. The voltage of the power supply of microcircuits with the letter indices V, G and D can be increased to 12 V, which will allow you to obtain more voltage output signal.

Another measuring generator, with which it is desirable to equip the radio engineering design club, the 3Ch-PCH1 generator (Fig. 62). It produces a signal 34 with a frequency of 1 kHz and an amplitude-modulated IF signal with a frequency of 465 kHz. The device is intended for testing and adjusting amplifiers 34 and IF paths of superheterodyne receivers. It can be powered from any DC source with a voltage of 12... 15 V, for example from three 3336L batteries connected in series.

Rice. 62. Generator 34-FC on block assembly BS-1 Developed by G. Shulgin (Moscow).

A characteristic feature of this measuring generator is that it uses the BS-1 block assembly as active elements—a small-sized unit that combines two bipolar transistors in its housing structures p-p-p and two field-effect transistors with an i-type channel. Appearance and numbering of pins of microassembly elements are shown in the same fig. 62 (left). In the generator diagram, the transistors are shown without circles symbolizing their cases, because the transistors of the assembly do not have cases. If the circle does not have BS-1 assemblies at its disposal, then instead of them, it can be used in mounted generators bipolar transistors KT315 series with a static current transfer coefficient of at least 50 and field-effect transistors of the KP303 series with any letter index.

This measuring device, recommended for repetition in radio engineering design circles of 2-fo year classes, consists of an IF signal generator on transistor VI, a signal generator 34 on transistor V3, and an amplitude modulator on transistors V2 and V4. Transistor VI of the IF generator is connected according to a circuit with a “grounded” (at high frequency - through capacitor C2) base.

Transistor operating mode DC is determined by the voltage divider R1R2 in the base circuit and resistor R3 in the emitter circuit, and the frequency of the generated oscillations is determined by the parameters oscillatory circuit, formed by inductor L1 and capacitors SZ-C5. Self-excitation occurs due to capacitive coupling between the collector and emitter of the transistor.

Generator 34, like the single-transistor generator assembled according to the circuit in Fig. 60, is a cascade covered by positive feedback through a double T-filter consisting of resistors R7-R9 and capacitors C7-C10. The frequency of the generated oscillations depends on the ratings of these elements and in this case is 1 kHz.

The voltage of the IF generator through capacitor C6 is supplied to the gate of field-effect transistor V2, and the voltage of generator 34 through capacitor SP is supplied to the gate of transistor V4. Thanks to serial connection channels field effect transistors, the combined effect of the voltages of both generators on their gates leads to the fact that the IF voltage is modulated in amplitude. From the output of the modulator (the connection point between the source of transistor V2 and the drain of transistor V4), the modulated IF voltage through capacitor C14 (it only passes oscillations of the IF) is supplied to socket X2 “IF”. The AF voltage from the output of the generator on transistor V3 is supplied to socket XI “AF”. Depending on what signal is needed to check or adjust the assembled structure, the generator probes are connected to the HZ “General” and X2 or X3 and X1 sockets.

Audio amplifiers or AF receiver paths are checked starting from the final stage. In this case, the probe is inserted into socket XI, and socket X3 is connected to the common wire of the radio device being tested.

To stabilize the frequency of the generated oscillations, the supply voltage of the device is maintained constant using a simple voltage stabilizer on the zener diode V5 and resistor R6.

A relatively small number of parts allows you to assemble a generator on a board with an area of ​​30...40 cm2 (for example, dimensions 60 X 60 mm). True, for this all parts must be small-sized: capacitors such as KM, KLS, resistors such as MLT-0.25, VS-0.125, etc. In the IF generator circuit, you can use an IF filter coil from transistor superheterodyne receivers. If necessary, the D814B zener diode can be replaced with a D809. The generator board with discrete transistors will be somewhat larger.

Setting up a measuring device practically comes down to setting the IF generator to a frequency of 465 kHz. It is convenient to monitor the operation of the probe generators using an oscilloscope connected to the gate of transistor V2. When the power is turned on, a characteristic image of amplitude-modulated oscillations with a modulation depth of about 30% should appear on its screen. The modulation depth can be easily calculated by measuring the largest (U max) and smallest (U min) range of modulated oscillations on the oscilloscope screen: m = (U max - U min) / (U max + U min).

If generator 34 does not self-excite, then capacitors with a capacity of 0.002...0.01 μF will have to be connected in parallel with the capacitors of the double T-bridge.

The IF generator frequency corresponding to 465 kHz is set using an industrial broadcast superheterodyne with the same intermediate frequency. Bringing the generator as close as possible to antenna socket or the magnetic antenna of the receiver, the tuning core of the loop coil L1 (and if necessary, then by selecting the capacitor C3) achieve the appearance in the dynamic head of the receiver of the maximum volume of sound with a frequency of 1 kHz (approximately the sound “mi” of the second octave). The precise tuning of the generator to a frequency of 465 kHz will be indicated by the constant sound volume when the receiver is tuned in any range.

Intermediate and high frequency measuring generators are used when setting up and testing the amplification path of IF and RF receivers of direct amplification and superheterodynes, as well as calibrating the receiver tuning scale.

Oscillating intermediate frequency generator. If you have an oscilloscope, IF filters can be accurately and quickly adjusted using a special generator, the frequency of which changes synchronously with the horizontal scan of the beam on the screen of the electronic oscilloscope. Here they can be used as complex standard sweep generators industrial production, as well as simple amateur designs, such as the one developed by one of the radio amateurs from the GDR. In Fig. 82, and a schematic diagram of this generator is presented, and in Fig. 82, b its operating characteristics, as well as an approximate view of the image on the screen of an electronic oscilloscope of the amplitude-frequency characteristic of the IF path of the receiver under test (Fig. 82, c).

The device consists of a master self-oscillator IF on transistor T1. the generation frequency of which is controlled by changing the capacitance r-n transition diode D1 and output emitter follower on transistor T2. Diode D1 is connected in parallel to the resonant circuit L2C5. Capacity p-p The transition of diode D1 changes under the influence of external voltage supplied from the horizontal scan generator of the oscilloscope to socket Gn1. As a result, the frequency of the generated oscillations changes. A change in the voltage on Gn1 in the range from 0 to -5 V leads to a change in the generated frequency by 120 kHz (from 380 to 500 kHz), and in the area marked with the letters A and B, an almost linear dependence of the generation frequency on the sweep voltage is observed. When connecting the output of the generator (Gn2) to the input of the intermediate frequency path of the superheterodyne, and the input of the vertical deflection channel of the oscilloscope to the output of this path, an image similar to Fig. 1 will be obtained on the oscilloscope screen. 82, v. By adjusting the capacitors or cores of the corresponding circuits, we achieve the required shape of the amplitude-frequency characteristic of the IF path.

In the manufacture of the described generator, you can use transistors P422, P423 or GT309A-GT309V. It is advisable to use zener diodes D815G, D816D, D809-D811 as diode D1. The inductance of coil L2 should be 0.48 mH, L1 - half that. In the case of using armored unified cores made of ferrite 600NN or F600, the coils are wound with PEV-1 0.12 wire. They must contain 147 turns (L2) and 100 turns (L1).

If necessary, the generator can be used without an oscilloscope, for example, to calibrate the scale of another device. In this case, the generation frequency is changed using a variable resistor R4, which regulates the initial bias voltage on diode D1.

Generator for setting up HF, IF and LF receiver paths.

In Fig. 83 shows a schematic diagram of a simple generator designed for setting up direct amplification RF receiver paths, as well as IF and LF superheterodyne paths. The generator is a multivibrator on two transistors T1 and T2, which simultaneously generates low-frequency pulses and oscillations modulated by them at an intermediate frequency of 455 kHz. The frequency of low-frequency oscillations depends on the parameters of the elements of the basic circuits of transistors (resistors R3, R4 and capacitors C2, C3), and the high-frequency oscillations depend on the data of the resonant circuit L2C5. Powered by generator low voltage(2-3 V). As a power source, you can use two galvanic elements 316, 343 or 373. The output oscillations LF and HF (simultaneously) are removed from resistor R2 through capacitor C1.

Transistors can be of type P422 or P423, GT309, GT322 with any letter indices. Inductors L1 and L2 are wound with PELSHO 0.12 wire on a two-section frame placed in a unified armored core made of ferrite grades 400NN, 600NN, F600. They contain 10 and 100 turns, respectively. The intermediate frequency of 455 kHz is used only in foreign superheterodynes, therefore, to set up domestic receivers, the L2C5 circuit must be tuned to a frequency of 465 kHz.

When setting up the generator, select the resistance of resistors R3 and R4 until stable generation is obtained at high and low frequencies, and also adjust the L2C5 circuit to the required frequency. The functionality of the generator can be checked using a broadcast receiver that has a medium wave range and a pickup input. Initially, the output of the generator is connected to the input of the pickup and by selecting the resistances of resistors R3 and R4, a loud and clear sound is achieved. In this case, the collector currents of both transistors must be equal. The frequency of low-frequency oscillations can be adjusted by changing the capacitance of capacitors C2 and C3.

After the installation of the low-frequency parts of the generator is completed, the L2C5 circuit is tuned, for which the output of the generator is connected to the antenna input of the receiver tuned to the second or third harmonic of the frequency of the IF generator, i.e. 2X465 = 930 kHz or 3X465 = 1395 kHz, corresponding to wavelengths of 322 m and 215 m. During normal operation of the IF generator, a strong hum should be heard in the receiver, which reaches maximum volume at a certain specific position of the tuning core of the inductor L2. This maximum will correspond to fine tuning of the generator to a frequency of 465 kHz.

If there is no generation at an intermediate frequency, then it is necessary to check the correct connection of the inductor terminals. When winding coils in one direction, the beginnings of the windings should be turned on as shown in Fig. 83, where they are indicated by dots.

Shortwave observer signal generator. Receivers used by radio amateurs and shortwave observers require: high demands in terms of accuracy and stability of the tuning scale markings. Therefore, it is necessary to periodically monitor and adjust the scale markings using special standard signal generators, for example, a generator assembled according to schematic diagram, presented in Fig. 84. This generator is made with only two transistors and generates grids of modulated frequencies that are multiples of 1 MHz or 100 kHz. They move from the first grid to the second using switch B1. The device uses transistor T1 to assemble a self-oscillator, the frequency of which, depending on the range, is stabilized by quartz PE1 at a frequency of 1 MHz or quartz PE2 at a frequency of 100 kHz. The oscillations of the self-oscillator are modulated in amplitude using a low-frequency generator assembled on transistor T2. The output high-frequency amplitude-modulated voltage is removed from the collector of transistor T1 and through the isolation capacitor C7 is supplied to the Gn1 “Output” socket. A small antenna in the form of a metal pin about 40 cm long is attached to this socket. The device with the antenna is placed near the antenna input of the controlled receiver. At the same time, the power it emits is sufficient for reliable reception of its signals on all short wave bands.

When switch B1 of the device is in the “1 MHz” position, you can control the accuracy of marking the receiver scale at frequencies that are multiples of an integer megahertz: 7.0 MHz, 14.0 MHz, etc. In switch B1 position “0.1 MHz” you can check the accuracy of the scale markings every tenth of a megahertz, for example 14.1; 14.2; 14.3 MHz, etc.

To manufacture such a generator in an American magazine that published a description of this design, it is recommended to use standard quartz resonators, 0.5 W fixed resistors, ceramic and film capacitors, silicon transistors, a germanium diode and a battery from a pocket receiver. The inductance of coil L1 should be such that it can be adjusted by a tuned core within the range of 60-140 μH, L2 - 810-860 μH. The body of the device is made of metal. This is necessary to eliminate uncontrolled radiation from the device and protect it from external influences.

When setting up the generator, select the resistance of resistor R1 at which stable generation is established in both ranges, and the resistance of resistor R3 at which the shape of low-frequency oscillations will be the best. The range of overlapped frequencies is adjusted by adjusting the cores of the inductors. The shape of the generated HF oscillations, which determines the number of harmonics of the fundamental frequency, also depends on their position.

The device can be used domestic transistors KT312 or KT315 with any letter indices, diode D1 type D18 or D20, D9V, transformer Tr1 from any pocket receiver or from a set of parts for assembling such a receiver. Capacitors C4 and C6 must be paper, type MBM for a voltage of 160 V, all others are ceramic KT-1a and KLS-E. The power source can be a Krona-VTs battery.

The IF generator is assembled on element DD1.4. Its feedback circuit includes a circuit formed by an inductor, capacitors C1 - C4 and a varicap VD2. Two control voltages are supplied to the varicap, one of which is constant (supplied through R1 - R4) and determines the central frequency of the generator, and the second is sawtooth (supplied through R17C6), it determines the swing band.
The center frequency is switched by changing the inductors L1 and L2 with switch SA1. This was done in order to simplify the setup of the device and make a single scale for resistor R17.
From the capacitive divider C2 and C3, part of the voltage of the IF generator is supplied to a buffer stage on transistor VT2, at the output of which smooth (R16) and step regulators (R19 - R21) of the output voltage are installed.
The following parts can be used in the design: microcircuits - K176LE5, K561LA7, K176LA7; transistors - KT315, KT312, KT3102 with any letter indices; diode VD1 -KD509, KD521A, KD522B, D220, D223; varicap - KB104A-KB104E, KB119A; capacitor C9 - K50-3, K50-6, K53-1, the rest - KLS, KM, KT; power switch - P2K, MT1; resistors R2, R16-R18-SP, SPO, SP4-1, R5 -SP3-3, the rest - BC, MLT. The coils are wound on frames from the IF coils of the Alpinist-407 radio receiver and contain 350 (L1) and 310 (L2) turns of PEV-2 0.08 wire, multilayer winding.
Most of the generator parts are located on printed circuit board made of foil PCB. All variable resistors, fixed resistors R19 - R21, capacitors C7 and C9, as well as output sockets and switch Q1 are located on the front panel.
Setting up the device comes down to calibrating the scales of resistors R2 and R17 and setting the required sawtooth voltage shape. To do this, first connect an oscilloscope (Rin = 1 MOhm) to the output of element DD1.3 and use resistor R5 to achieve an undistorted “saw” shape. Changing its amplitude is performed by selecting the resistance of resistor R9. The “saw” frequency can be changed by selecting the capacitance of capacitor C5.
Then a frequency meter is connected to the output of the IF generator, resistor R2 is set to the middle position, and R17 to the bottom (according to the diagram). Using the magnetic circuit of coil L1, the frequency is set to 465 kHz, and L2 - 500 kHz, then the scale of resistor R2 is calibrated in both subranges and, if necessary, by selecting resistors R1 and R3, the required tuning range and its symmetry with respect to the central frequencies are achieved.
Then the scale of resistor R17 is calibrated. To do this, the synchronization voltage is supplied to the X input of the oscilloscope from the XS1 socket of the IF generator, and to the Y input of the oscilloscope - a signal from the XS4 socket ("IF Output" 1:10) of the IF generator and through a 100 Ohm resistor from a standard high-frequency generator, which is used as reference Resistor R18 sets the sweep length to the width of the entire oscilloscope screen. After this, by rotating resistor R17 and changing the frequency of the reference oscillator, the scale of resistor R17 “Swing Band” in kHz is calibrated according to the zero beats on the oscilloscope screen.
The IF generator should be powered from a stabilized source with a current of at least 20 mA.

I. NECHAYEV, Kursk, Radio No. 9, 1993, p. 20

A simple but extremely useful generator for express testing the ULF or radio path of the receiver.
The diagram is taken from the book “Know the Radio” by V. G. Borisov. A classic multivibrator adapted for modern element base(in the original transistors are germanium).

The generator works perfectly even with a supply voltage of up to nine volts (it did not supply any more), only the amplitude of the output signal increases proportionally (half the supply voltage), and in order not to damage the device under test, you will have to leave an additional resistor of about 0.7 -1 V.




The body is a twenty-cc syringe. “Minus” - with a collet clamp, output - instead of a needle. At the end there is a microswitch that disconnects the “plus” from the battery - there is a signal as long as it is pressed.
The sampler is easy to use. In the case of a simple test, the ULF “minus” is connected to “ground”, and the signal probe is connected to the input. A square wave should be clearly audible at the output of the amplifier. A more complex check is cascading, when the ULF did not work from the input. Then the generator is connected to each amplifier stage in turn, starting from the final one and moving to the very first one - where the sound disappears, that’s where you need to look for the problem.


The book says that the main frequency of the generator is 1 kHz, but mine turned out to be lower, about 230 Hz - probably due to the replacement of transistors. However, this meander is clearly audible. To increase the frequency, you can slightly reduce the values ​​of C1 and C2.
You can also use this generator to check the radio path of the receiver - just touch the signal pin to the antenna. In the Far East and Northeast, sound appears immediately; in the upper HF, it is less audible.
An example of checking the ULF “VEF 214” and “Ishima”.

Second version. Miniature. The output is on the left, from the “ceramics” 100 nF. Transistors - KT315V. Capacitance - 22 nF. Collector resistors - 3.9 kOhm. The frequency came out to be about 500 Hz.