FROM Instruments based on the radio. Technical progress is relentless it forces us to buy all new electronic devices, and old, but usable receivers, tape recorders, record players and tape recorders had moved into the closets and attics, and then to the dump. However, enthusiastic Amateurs on a more careful attitude to an old technique, finding it different application. So old, no one needs a radio superheterodyne scheme can certainly be found almost any Amateur radio.


Meanwhile, on the basis of such a receiver may be measuring a whole range of radios. In this modification of the receiver is done using standard electronic elements. Consider first the possibility of a radio of direct amplification.


Generators audio frequency (AF)
Using audio amplifier (uzch) and volume control of a radio receiver 13 and entering a positive feedback (PIC) through the condenser (Fig.1) obtained at certain ratios of values and the generation of electrical oscillations, pulsed or sinusoidal.
The generation of oscillations in uzch entered frequency selective PIC in the presence of uzch nonlinearity is not available in all frequencies. However, the novice radio Amateur enough to have a number of discrete frequencies, is determined mainly by the capacitance, and waveform is selected by the volume control R.
Due to the small volume of the body of the radio and to save money the switching frequencies can be realized by using a homemade switch on the base semisterile lamp panel installed on the housing of the radio receiver, and two forks out of copper wire, connected by a segment of flexible stranded wires. The seventh leg soldered the output wire uzch. Capacitors can be soldered directly on the legs of panels 1 — 6.
To simplify the problem, you can opt out of the switch and be satisfied with a small range of smooth change of frequency or to have a single discrete frequency.
Almost all radios have a Jack for external speaker or headphone This Jack is used as output for output of the generated oscillations AF. If you can attach the plug wire, then the generator can be used as a sound probe of the fluctuations of the AF can be submitted at any point custom equipment and test the signal on different circuits.
On the case you must also set the socket for feeding external audio signal uzch. In this case uzch can be used as a checklist when configuring a variety of equipment.
The generator can be turned into a sound sampler — it is enough to break the circuit PIC in a convenient place and ends output. This can be done using the already installed tube socket. One wire must use the fork to enter in one of the nests No. 1 to 6, the second — in the slot number 7. With the closure plugs uzch will generate fluctuations in the AF, by opening variations will be broken. Thus with the help of these probes it is possible to check the integrity of many electronic components — resistors, inductors, transformers, wires, cables, field rations, etc. If the studied item or the circuit tests normal, the generator will work in the dynamics of the sound will be heard. No sound is evidence of breakage or malfunction in the external circuit.
Fig. 1. General scheme for the construction of the low-frequency oscillator
Fig. 1. General scheme for the construction of the low-frequency oscillator
In the absence of space to accommodate the panels and capacitors task can be extremely simplified. Input socket uzch should be placed from the output (full-time) at this distance, so that the capacitor can be directly entered in the nest outside. From an operational point of view, this method of switching frequency is more advantageous as it allows to any grid frequency without carrying out any work with the scheme.
If you configure a device, the amplitude of the signal output uzch will be big, it can be reduced to the required value by including sequentially the resistor.
Generators of radio frequency (RF)
Signal generator (SG). In the receiver of direct amplification, there is always a radio frequency amplifier (RF amplifier) to amplify the signal of the received broadcasting stations operating in the bands long and medium wave (LW and MW), i.e. in the frequency range 150 to 1600 kHz. By entering in RF amplifier POS, you can get the generator of frequencies in this band continuously tunable over the entire range using standard variable capacitor.
To RF amplifier working as a generator, the number of stages must be even. Signal the PIC when it is removed from the collector load of the transistor of the last cascade and is fed into the base circuit of the transistor of the first cascade. If the number of stages is odd RF amplifier, the signal POS must be removed from the emitter load of the last stage. Alternatively, the signal POS can be removed from the collector load of the second cascade, and a third cascade RF amplifier to be used as a power amplifier of the oscillation. As the contour system uses a regular ferrite antenna. The RF signal can be removed also with a ferrite antenna, is wound on the coil connection (a few turns).
The RF signal is displayed on the Jack for external antenna. If such a socket is not provided in this particular design, you need to install on the case any high-frequency coaxial connector. High frequency cable of the type RK-50.
If a custom device with which the radio Amateur will be known to have a high sensitivity, no connectors and cables are not required. Since the ends of the ferrite antenna is not shorted, the whole system is an open, highly radiating circuit. So simply bring the RF generator to the device. Because an oscillating system RF amplifier no changes are introduced, the scale in the receivers of direct amplification serves as both the scale of generated frequencies.
The generator of standard signals (GSS)
For complete control of the parameters of the output signal of the RF generator needs to know the amplitude of signal supplied to a DUT.
Adjustment of the output level can be carried out step external divider (Fig.2) change it ten times (1:10; 1:100; 1:1000). It connects to the output plugs of the cable or directly to a coaxial connector simultaneously with the RF cable. The body of the divider is executed from thin copper or brass, each stage is mounted in a separate compartment, through the holes which are resistors of stages of division.
Divider set, tightly pressed against the case cover. After completing the configuration, that is, upon reaching the dividing signal ten times during the next stage, the lid is brazed to the housing around the perimeter.
Selective measuring radio
Reducing sensitivity of a radio receiver in the performance of normal about the procedure and the feeding at the antenna input AM signal from an external source, you can use it as a selective measuring device for determining the carrier frequency of the external source of RF. The AF signal is allocated a detector and amplified uzch, listening through the loudspeaker. Setting of the external RF signal source is determined by maximum sound.
If nepreodolimoe external signal, determine its frequency, by the method of zero beating. The method consists in comparing the frequencies of the two sources of RF in the mixing element, which can be used resistors, diodes, transistors. Generators RF single reference frequency, the second test, the frequency of which to be determined. At close values of the frequencies of both generators to a mixing element having beats — low-frequency oscillations, which disappear when the full equality of frequencies. The beat signal is amplified in uzch listening through the loudspeaker.
Using the constructed generator, standard detector and standard uzch, you can implement this method of determining the carrier frequency of the external source if the signal also apply to the detector. To increase the sensitivity of the method of zero beating the signal to an external source must be fed through a second detector having a common load with the standard. To input external signal, you must install a connector or socket or use the antenna input. Implement a method zero beating can be the other way. If the ferrite antenna is equipped with an additional winding for output fluctuations of the RF generator to the connector, the external signal source to this connector, it is possible to mix signals on the ferrite antenna and to highlight the mixed signal at the nominal detector, the second detector in this case is not necessary.
Aperiodic measuring amplifier
It can be useful when setting up various amplification devices and cascades, e.g., local oscillators or amplifiers of intermediate frequency (Ombudsman) in the radios, in various homemade products and devices.
The setting is at the maximum volume of the AF signal via the regular speaker. The external signal should be amplitude modulated. To implement aperiodic instrumentation amplifier, it is sufficient to disconnect the variable capacitor from the inductor circuit and the antenna input signal to the external source. PIC it should be disabled. If the receiver has no antenna input, an external signal can be fed into an additional winding located on the ferrite antenna, or just bring to the ferrite antenna, the emitter of the external signal, an open circuit or wire.
Test transistors
Very often the radio Amateur it is necessary to verify the integrity of the transistors and the static current transfer ratio.
Both tasks quite simply solved with the help of uzch, translated in the generator mode AF. To check the integrity of the transistor is sufficient in one of the first cascades У34 regular transistor to replace in the test. Moreover, if the scheme uzch built on transistors of different conductivity, then, replacing one or the other of the regular transistor in the test, we can reject transistors as p-n-p and n-p-n structures.
Accordingly, it will be necessary to remove two panels from the regular transistors on one of the panels of the case or, if the transistors are soldered directly into the PCB, unsolder them and outside to mount the bar with contacts, or two three – or five-pole connector from the tape — now the transistors, you can insert the findings in the sockets of the connectors or the contact strips.
Fig. 2. External divider
Fig. 2. External divider
To determine the gain you need to cascade URSC to check the transistors enter the on allowing to change the gain of the stage as a whole. Such a body could be the volume control uzch — variable resistor, is additionally introduced into the base circuit or the emitter of the transistor. It is clear that the generation of uzch POS is only possible for certain values of the gain of the transistor and the variable resistor. If you pick up a few transistors with different known values, then it is possible to construct a scale at different positions of the potentiometer in the moments of occurrence of generation.
The same cascade can be used to build a simple voltmeter. In the presence of its generation can be suppressed applying a barrier voltage to the base or the emitter of the measuring transistor of the cascade via a variable resistor. The higher the value of the measured voltage, the less has to be a resistor. Scale directly in volts can be calibrated according to the testimony of any voltmeter.
The methods and approaches to an even greater extent applicable in the alteration of the superheterodyne radio. The presence of the local oscillator, which is a essentially a signal generator (GS), significantly reduces the amount of work in finalizing the staffing of the cascades. And if the radio works on HF bands, the bandwidth of the signal generator will be substantially wider. However, the contours of the local oscillator must be reconstructed as frequencies on all bands above the specified scale to the value of the intermediate frequency (if) is 465 kHz. This will allow, first, to use the standard scale and to set the frequency of the HS and, secondly, most importantly, has been re-designed GS will allow you to configure the contours of radios operating in standard LW, MW and HF bands.
Made and designed in the form of an individual node of an RF probe made on the basis of details of the amplitude detector significantly extends the range of the work. Introduction one of the gain stages RF POS allows you to obtain the stand-alone generator P4 (HRU) with the exact frequency setting. A larger volume of superheterodyne design and a greater number of cascades give the possibility to install additional switching products and additional functional cascades. So, transferring one of the cascades P4 or uzch to the amplitude modulator, and by setting the appropriate switches and sockets, you can get additional modes of GS and HRU — amplitude-modulated oscillations, which significantly expands the scope of research. In addition, the presence of a superheterodyne is more than a receiver of direct amplification of the number of cascades allows to obtain by appropriate connections and even a receiver of direct amplification with high sensitivity.
Huge opportunities for the creation of high quality measuring instruments are open to ham alteration now a rare antique superheterodyne tube radio. For example, using vacuum tube diode (half bulb of the amplitude detector, for example 6Х2П or 6Х6С) and the first cascade uzch, you can get a vacuum tube voltmeter with an input impedance in the tens of Meg and its use for measurements in circuits containing field-effect transistors and CMOS circuits.
Transistor high-frequency generator, assembled on the mixing tube, in comparison with the generators on the triodes, enables a broader frequency range with higher stability. The presence of built-in capacitor of variable capacity allows you to create a generator of sound frequencies with continuously tunable frequency and sinusoidal waveform — essentially, another instrument of high class.
(To be continued)

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