Probe for testing receiver intermediate frequency amplifiers. Schemes and descriptions of measuring generators. Homemade measuring instruments

When repairing an audio amplifier or a household radio at home, it often becomes necessary to trace the passage of the signal through the cascades. And this causes certain difficulties in the repair of those radio amateurs who do not have the necessary instruments.
The simple generator probe brought to your attention is intended for repair of radio equipment. It does not contain winding units and is available in the manufacture, configuration and operation even for a novice radio amateur. The probe generator allows not only to check the health of the audio amplifier and the intermediate frequency amplifier path (IF 465 kHz) of the radio receiver, but also to adjust the IF circuits of the radio receiver according to the maximum signal level. Schematic diagram of the device is shown in Fig.1.
A low-frequency generator is assembled on transistor VT1, which generates oscillations with a frequency of approximately 1 kHz (determined by the parameters of the phase-shifting circuit C1C2C3R1R2 included in the OOS circuit).
The output signal is fed to the base of the VT2 RF generator through a single-stage R5C5 low-pass filter, which cleans up the output signal from harmonics and reduces its amplitude to obtain an AM modulation depth of approximately 30%.
The high-frequency generator operates at a frequency of 465 kHz and is made according to the capacitive three-point scheme (Klapp's version), only a ceramic resonator ZQ1 is used instead of an inductor. In this scheme, the generation of oscillations is possible only with the inductive resistance of the resonator circuit, i.e. the oscillation frequency is between the frequencies of series and parallel resonances. A small-sized ceramic filter FP1P1-61-02 was used as a resonator (marking without color marks).
FP1P1-61 series filters widespread, not expensive and, most importantly, with the inclusion indicated in the diagram, they have a small spread of parameters in the generation frequency. I tested the batch of 7 pieces that I have and I want to note that the actual spread in the generation frequency did not exceed + -0.5 kHz (according to the specifications, it should not exceed + - 1 kHz). That. when using virtually any filter from the FP1P1-61 series, it is guaranteed, without adjustment, to obtain a test signal with a frequency of 465+-1 kHz, which is what we actually need. The emitter VT2 is loaded on a resistive divider R7R8, which lowers the output signal to practical levels and ensures a stable operation of the generator, regardless of the connected external circuits (device under test). Potentiometer R9 serves for smooth adjustment of the output signal level.
With the position of the switches indicated on the diagram, the output of the probe generator will be an AM signal with a frequency of 465 kHz, modulated by a low-frequency signal of 1 kHz (30% modulation). In this case, if you turn on SA1, then only a signal of an unmodulated IF carrier of 465 kHz will appear at the output, if you turn on SA2, then only a low-frequency signal with a frequency of 1 kHz will appear at the output.
Transistors can be used any RF (KT315, KT3102, BC847, 2N2222, etc.) With H21e within 100-220, otherwise you will need to select R4 to get 4.5 + -0.5V on the VT1 collector.
Powered by Krona, installation can be any available to you - on a breadboard, signet or hinged.

Figure 17 shows a schematic diagram of an oscillator that can be used to tune the intermediate frequency path in radio receivers for various purposes. The frequency of the output signal of the generator - fp=465 kHz * - is set by the quartz resonator ZQ1, and its amplitude - not less than 2 V - depends on the voltage of the power supply Upit.

All resistors in the generator are of the MLT-0.125 type, KM-6 capacitors or the like. Transistor VT1 - almost any n-p-n having a current gain of at least 100 and a cutoff frequency of at least 100 MHz.

Rice. 17. Generator for tuning the IF path of the radio receiver

The generator does not require adjustment. It may take only a few
increase the capacitance of capacitor C2 (up to 6200 .... 6800 pF).

With such an amplitude of the output signal, the generator does not need to be connected to the radio receiver - it is enough just to bring them closer. But the output signal level can be reduced, brought to the desired level. So, for example, as shown in Fig. 18. But in this case, the generator itself will need to be placed on the screen (a fragment of it is shown by the dashed line), otherwise the pickups "through the air" will not allow a signal of a sufficiently low level to be obtained at its output. With good screening of all circuits, the resistor divider can be made stepwise (Fig. 19), the output signal of which can be reduced, if necessary, to fractions of a microvolt. The calculation of such divisors is described in.

Rice. 18. Simple output voltage divider

Rice. 19. Stepped output voltage divider

*) The carrier of the IF path fp=465 kHz is a domestic standard. In foreign communications technology, more often fp = 455 kHz. To set up such equipment in the generator, you only need to change the quartz resonator.

Setting up a radio receiver or the receiving part of a radio station is a rather complicated process that requires both increased attention and careful execution. The whole process of setting up a VHF receiver should be divided into three stages.

First, you need to check the correct installation and performance of each stage, starting with the lowest frequency, i.e. you need to start from the "end" of the scheme.

Rough tuning of all oscillatory circuits included in the receiver. This setting should also start from the "end". Tuning is usually carried out using a sufficiently strong RF signal of the required frequency applied to the input of the receiver.

Fine tuning of all receiver circuits, especially UHF. Tuning is carried out when a very weak, at the noise level, RF signal of the required frequency is applied to the receiver input. The final point of tuning should be to make a measurement and perform a calculation of the noise figure of the UHF receiver.

All these setup steps can be done using homemade measuring instruments.

To carry out a rough adjustment of a VHF receiver or converter, a signal from a simple noise generator should be applied to its input. A diagram of such a simple device is shown in Fig. 1. You can also make and use a slightly more complex device, the diagram of which is shown in Figure 2.

Fig.1 Schematic diagram of the simplest noise generator:

Fig. 2 More complex noise generator:

When setting the converter to 29 MHz or 145 MHz, immediately after connecting the noise generator to the UHF input, a noise signal will appear at the output of the receiver. Trimmers - (capacitors) should achieve the maximum possible amplification of the noise signal.

Only a rough adjustment can be made in this way. Often this setting is sufficient. Fine-tuning a VHF receiver or converter and checking the directional properties of the antenna can be done using more sophisticated instruments.

Receiver Fine Tuning

As a result of the fine tuning of the receiver, the maximum possible sensitivity of this receiving device should be achieved.

The sensitivity of the receiving device is one of the most important parameters that determine the potential of the entire work of the creator of the device. Therefore, of great interest are objective methods for determining and comparing the sensitivity of various receivers that are available for amateur (home) conditions.

The most accessible, and therefore the most common way to determine the quality of the receiver is to listen to the signals on the air. Obviously, the accuracy of such estimates is extremely low, since the signal level of a remote radio station can vary by tens or even hundreds of times.

Gennady A. Tyapichev - R3XB (ex RA3XB)

The IF generator is assembled on the element DD1.4. Its feedback circuit includes a circuit formed by an inductor, capacitors C1 - C4 and a varicap VD2. Two control voltages are applied to the varicap, one of which is constant (supplied through R1 - R4) and determines the center 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 the switch SA1. This is done in order to simplify the setup of the device and make a single scale of the resistor R17.
From the capacitive divider C2 and C3, part of the voltage of the IF generator is fed to the buffer stage on the transistor VT2, at the output of which smooth (R16) and step regulators (R19 - R21) of the output voltage are installed.
The following details 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, KV119A; 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 - VS, 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 placed on a printed circuit board made of foil textolite. All variable resistors, fixed R19 - R21, capacitors C7 and C9, as well as output sockets and switch Q1 are located on the front panel.
Establishing the device comes down to grading the scales of resistors R2 and R17 and setting the required sawtooth voltage shape. To do this, first connect an oscilloscope (Rin = 1 MΩ) to the output of the element DD1.3 and resistor R5 achieve an undistorted "saw" shape. The change in its amplitude is performed by selecting the resistance of the resistor R9. The frequency of the "saw" can be changed by selecting the capacitance of the capacitor C5.
Then, a frequency meter is connected to the output of the IF generator, the resistor R2 is set to the middle position, and R17 to the lower position (according to the diagram). The magnetic circuit of the coil L1 sets the frequency to 465 kHz, and L2 to 500 kHz, then the scale of the resistor R2 is calibrated in both subranges and, if necessary, by selecting resistors R1 and R3, the required tuning range and its symmetry relative to the central frequencies are achieved.
Then calibrate the scale of the resistor R17. To do this, the X input of the oscilloscope is supplied with a synchronization voltage from the XS1 socket of the IF generator, and the signal from the XS4 socket ("IF output" 1:10) of the IF generator and through a 100 Ohm resistor from the exemplary high-frequency generator, which is used as reference. Resistor R18 sets the sweep length to the width of the entire oscilloscope screen. After that, by rotating the resistor R17 and changing the frequency of the exemplary oscillator, zero beats on the oscilloscope screen calibrate the scale of the resistor R17 "swing band" in kHz.
The inverter generator should be powered from a stabilized source with a current of at least 20 mA.

Homemade appliances

I. NECHAYEV, Kursk
Radio, 2000, No. 8

Radio receiving paths various equipment (radios, radios, CB transceivers, etc.) contain such units of the same type as audio frequency amplifiers (3CH), intermediate frequency amplifiers (IF) of FM and AM stations. They have to be checked when repairing equipment in the first place. The one proposed here will help with this. probe-generator.

This relatively simple instrument generates 1 kHz 3CH pilot signals and 10.7 MHz and 465 (or 455) kHz modulated IF signals. The amplitude of each signal can be smoothly adjusted.

Device diagram

The basis of the device (Fig. 1) is a generator based on a transistor VT1. Its operating modes are set by the switch SA1. In the position shown in the diagram ("3H") of the switch, the supply voltage of the battery GB1 is supplied through the resistor R9 to the transistor and the generator starts to operate at a low frequency. It is determined by the frequency-setting chain R2C3R3C4R5C5 in the transistor feedback circuit.

In the switch position "465", the supply voltage to the transistor is supplied through the resistor R10, while the VD1 diode opens and the ZQ1 filter is turned on in the feedback circuit of the transistor stage. 3H (1kHz) and AM IF (approximately 465kHz) are generated, while the IF signal is modulated by the 3H signal. The R1C1 filter eliminates high-frequency feedback through capacitors C3-C5, ensuring stable operation of the oscillator at the IF.

When the switch is set to the "10.7" position, the supply voltage to the transistor is supplied through the resistor R11. The VD2 diode opens, and the ZQ2 filter is included in the feedback circuit. The generator will operate at 3H (1 kHz) and IF FM (approximately 10.7 MHz). The IF signal is modulated with a 3H signal.

The generated signals through the resistor R12 and the capacitor C8 are fed to the output voltage regulator R13, and from its engine to the output sockets X1 and X2.

In the switch position "Off." the power supply is disconnected from the generator.

In addition to that indicated in the diagram, transistors KT3102A-KT3102D, KT312V can be used in the device. ZQ1 filter - any of the FP1P-60 series, narrower band is better. At a frequency of 455 kHz, a foreign-made filter should be used. The ZQ2 filter is a bandpass piezoceramic filter at a frequency of 10.7 MHz, domestic (for example, FP1P-0.49a) or similar imported. Capacitors - K10-7, K10-17, KLS or small imported ones. Trimmer resistor R2 - SPZ-1b, variable R13 - SPO, SP4, the rest - MLT, S2-33. Switch - any small-sized switch for one direction and four (or more) positions. Power source - voltage 4.5 ... 12 V. These can be series-connected galvanic cells, batteries, a Krona battery, or a source of a tested design.

Most of the parts are placed on a printed circuit board (Fig. 2) made of one-sided foil-coated fiberglass.

It is placed in a plastic case of a suitable size, on which a variable resistor R13 is installed, sockets X1, X2 (Fig. 3). A probe is inserted into one of the sockets, depending on which nodes are being checked. The common wire is led out through a hole in the housing and is provided with a crocodile clip. In the case when the power supply is built-in, it is necessary to provide a place for it in the case. The installation of capacitors C7, C9, SU is carried out by the method of surface mounting.

Instead of a filter at a frequency of 465 kHz, you can put a filter at 455 kHz - then the generator will operate at this frequency. It is permissible to use a five-position switch and enter this frequency additionally. The new filter must be enabled in the same way as the ZQ1. If external power is planned, a new frequency can be set using the released switch contact.

You need to configure the device at the voltage with which it will work. Current consumption - within 0.5 ... 3 mA, depending on the supply voltage.

Then, the generation is checked in the switch position "465" (or "455") and by moving the slider of the resistor R2, stable generation of 3H and IF signals is achieved at the switch positions "465" ("455") and "10.7". If the generation is unstable in the "3H" position, you will have to select the resistor R9.

The probe is used as usual, applying signals to certain points of the device under test.