|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Amateur GSS. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology GSS is intended for various measurements in amateur practice as a source of sinusoidal voltage of sound (AF) and radio frequency (RF). Possesses, according to the author, rather high metrological characteristics. The frequency range of 15Hz ... .44,5MHz is covered by two generators: sound (GZCH) and radio frequency (GRCH). In this case, the first provides, if necessary, the amplitude modulation of the second. A feature of the GFR is the rigid stabilization of the output voltage amplitude regardless of frequency, the presence of a resonant amplifier, control of the carrier level and modulation depth, the presence of a sufficiently accurate attenuator to obtain a calibrated output voltage at a matched load of 75 ohms. GZCH is a slightly reduced version of the generator described in [1]. Both generators have additional internal outputs for feeding a signal to a frequency meter, which is included in one set with the GSS. Technical specifications GZCH
HGH
Schematic diagram of the GSS is shown in Fig.1.
The HRF consists of a master oscillator (VT1, VT2), a source follower (VT4), a resonant amplifier-modulator (VT6), an output matching amplifier (VT7, VT8), an attenuator, output level control and stabilization circuits (DA6, DA7), an additional RF output to the frequency meter (VT3, VT5, VT9). The master oscillator is assembled according to the inductive three-point scheme. Transistor VT1 turns on "to help" VT2 in subranges 4 and 5 due to an increase in VT2 drain current through resistor R7. The choice of R1…R5 and the installation of two-sided limiters VD1…VD10 provide preliminary stabilization of the amplitude with minimal distortion. The amplitude of the RF voltage at the output of the source follower VT4 is in the range of 1,1-1,3V in all subranges and only in the fifth can it reach 1,8V. Further, through the corrective circuits R11, R12, C7, C8, the RF voltage is supplied to the first gate of the resonant amplifier - modulator VT6. On four subranges, a transformer connection with the circuit was used to equalize the load of the cascade, on the 5th - the complete inclusion of the circuit in the drain circuit. The amplifier circuit is rebuilt simultaneously with the master oscillator circuit. Switching of subbands is carried out by switch SA1. At the same time, it is modified in such a way that sections SA1.2 and SA1.5 close the loop coils of all non-working sub-bands, the frequencies of which are lower compared to the included ones, to the body. The schematic image of these sections is trying to reflect the design, which will be discussed below, and the author did not find a generally accepted image of such a case. From the amplifier circuit of the voltage modulator, it enters the matching stage - a composite follower (VT7. VT8), the load of which is R31 - a smooth RF level controller. R31 is calibrated from 0,1 to 1 mV. From the R31 engine, through the matching circuits, the signal is fed to the input of the step attenuator. The circuit ensures that the output impedance of the RF level control is constant. The attenuator is a set of dividers from 0 to 80dB through 20dB, switchable by SA2. In the "X100" position there is no attenuation, in the "X10" position the 20dB step is turned on, in the "X1" position - two steps of 20dB each, in the "X0,1" position - two steps of 30dB each, in the "X0,01" position - three the attenuation steps are 27,26 and 27 dB, respectively. Sections SA2.2 and SA2.3 close to the case all the inputs and outputs of the attenuator, which have a lower degree of attenuation compared to the selected one. From the output of the attenuator, the signal goes to SW2 of the RF output, to which a load with an additional attenuation of 75dB is connected via a 70 ohm RF cable 20 cm long. It is necessary to pay attention to the values of the attenuator resistors and adjacent circuits (R38….R56). These denominations were obtained by calculation and rounded to within ±0,25%. The control of the output voltage of the HRF is carried out at the connection point of the VT8 collector and the level controller. Here, a level of 1V must be strictly maintained by means of a stabilization circuit. To do this, the voltage is rectified by a detector with a doubling of VD14, VD15 and processed by the op-amp DA6 with compensating diodes VD18, VD19 in the feedback circuit. The initial bias current flows through the diodes thanks to R82, R83. If all the mentioned diodes are sufficiently identical to each other, then we get a fairly linear detector characteristic from a tenth of a volt to a unit of a volt. The voltage from the output of the detector is compared by DA7 with the reference voltage set by the tuning resistor R92. The output of DA7 is fed to the second gate of the amplifier - modulator, which is what stabilizes the output voltage of the MFR. If, from the output of the GZCH through the circuit R91, C58, an audio frequency voltage is applied to the circuit for generating a reference voltage, then we get amplitude modulation. The depth of modulation is controlled by changing the output voltage of the GZCH. To obtain an additional unmodulated RF output to the frequency meter, the signal is fed to the VT3 gate, then to the VT5 base. From the VT5 emitter, the voltage through the diode switch VD11, VD12 and then through another VT9 follower is fed to an additional RF output. The diode switch is controlled from the power supply via the XT1 contact. When the frequency meter is turned off, minus 1V voltage is supplied to the contact XT12 from the power supply instead of + 12V, which causes the diode switch and transistor VT9 to lock. The apparent circuit "excesses" are explained by the requirement to exclude RF penetration through an additional output when checking highly sensitive equipment, when it is necessary to turn off the frequency meter to eliminate interference and, at the same time, to avoid the influence of the state of the diode switch on the frequency of the master oscillator. The GZCH is assembled on the op-amp DA2 ... DA4 and the transistor VT10 and practically repeats the design described in [1]. To reduce the constant component at the output of DA2 ... DA4, balancing resistors are installed. Cascade VT11, VT12 provides an additional AF output to the frequency meter. To control the output level of both generators, a DA5 peak voltmeter with a PA1 measuring head is used. The appearance of the output meter scale is shown in Fig.2.
The upper scale is calibrated in effective values, the lower one in percent modulation. The voltmeter output switch is interlocked with the GRCH switch, and when the latter is de-energized, the voltmeter input is switched to the GZCH output. On the upper scale, the audio frequency voltage is read at the output XS4 “x1". If the MRF is turned on, the voltmeter is connected to the output of the detector, or rather to its divider R86. In the absence of modulation, the meter needle should clearly be against the 1V mark on the upper scale and against 0% on lower at any frequency, which indicates the normal operation of the MGF output voltage amplitude stabilization circuit. When the MGZ output voltage increases from zero, the modulation depth is read on the lower scale. and an output divider. The applied peak voltmeter has some drawback that must be taken into account in the work. The inertia of DA31 at frequencies above 5 kHz affects: at frequencies of 10 kHz, the blockage is 20 dB, at a frequency of 1 kHz - 100 dB. When measuring the output voltage of the HRF, this does not affect, since it has its own detector. HRF and GZCH have separate power switches. The VT13 cascade switches minus 12V for the HRF due to the lack of SA4 contacts. The supply of the master oscillator and the amplifier - + 8V modulator is provided by the DA1 microcircuit stabilizer. All the main components of the HRF are located in the RF unit with double shielding. The HF block with dimensions 132x62x90mm is soldered from double-sided foiled glass textolite 1,5mm thick. The design of the RF block (top view) is shown in a simplified way in Fig.3.
The top, bottom and side walls are brazed with four tinplate corners placed over the corners. The generator is separated from the attenuator by a longitudinal partition, and they, in turn, are divided into compartments by transverse partitions, the joints are soldered. After installation and debugging, the compartment covers were soldered. The outer sides of the RF unit do not have electrical contact with the inner screens. Thin-walled brass tubes with a length of about 32 mm and an inner diameter of about 5 mm from the knee of the telescopic antenna are soldered into the attenuator partition. Attenuator resistors are placed inside the tubes as shown in callout A of Fig. 3. For the GSS case, a cast case of an unknown purpose made of aluminum alloy was used, with front and rear covers, with internal partitions. The RF block is placed inside this case, the inner shield of the block is connected to the outer case at one point by the outer sheath of the RF cable segment connecting the attenuator output to the XW2 output jack. The XW2 socket is located on the front cover of the outer housing. The axes of the HCG controls are isolated from the outer case by insulated extension cords or tubes. The KPE block (from "Speeds") is connected through the friction clutch to the knob for smooth frequency setting. The installation is carried out by small functional modules on boards made of double-sided foil-coated fiberglass in a planar manner. Printed circuit boards were not developed. Tracks and pads were cut with a cutter. The data of the coils of the circuits are placed in table. one. Table 1
Coils of sub-ranges 1…3 are placed in armored cores made of carbonyl iron SB-12a and wound in bulk on three-section frames, and sub-ranges 4 and 5 are wound in a single layer on polystyrene frames ø5,5 mm, having trimmers made of carbonyl iron RM4x11,5 (such frames were used in TVs "VL-100", "Electronics"). The coupling coils are wound in the middle sections of the multi-split coils, and the L11 coil on top of the L15 is stepped with it from the ground end. Trimmer capacitors C17 ... C21 small-sized imported production with a capacity of 2 ... 10 pF. Switches SA1 and SA2 used type PG3-5P10N with revision. Extra sections are removed, and two sections of each are finalized. One of the two "knives" in the section is removed and replaced with a wider one. Extra contacts are deleted. The result is shown in Fig.4. On the left - the initial position "1" in accordance with the diagram. The wide "knife" sector is not involved in the work. On the right - position "4", in which the wide sector closes the conclusions from the first to the third to the case. Switch SA3 type PR-4P4N. Resistor R61 type SP3-30g with functional characteristic A. Resistors R31, R64, R74, R92 type SP4-1a, wire resistor R86 SP5-1v, R68, R80, R84 - SP3-19b.
It is better to balance the op-amp before installation and install it with selected fixed resistors. About resistors R38 ... R56. The best option is C2-10 of the closest denominations of the E192 series. The author failed. In fact, about 20 pieces of the nearest lower value of resistors, similar to MLTs, were bought in the store. Suitable specimens were selected with a 0,25% class digital instrument. If necessary, their size was adjusted on a thin emery wheel, followed by oil varnishing. Of particular note: the purchased resistors did not have helical threads. For the selection of diodes VD14, VD15, VD18, VD19, 24 samples were taken and the I–V characteristics were taken for all at currents from 0,05 to 4 mA. According to the characteristics, the four closest ones were selected. As a meter, a head from a M42100 class 1,5 voltmeter with a total deflection current of 1 mA was used, which was placed in a small-sized case from the level indicator of the Vesna tape recorder.
Chokes for 100 µH - standard, L19, L20 - any type with an inductance of at least 1 mlH. SA4, SA5 - microtoggle switches MT-3. External views of the GSS are shown in Fig. 5 and Fig. 6. Figure 7 shows the appearance of the GSS with a stabilized power supply and a frequency meter in one unit. With proper installation and pre-balancing of the op amp, mode adjustment is not required. At the beginning, the GZCH is adjusted, which is described in detail in [1]. Resistor R64 sets the maximum voltage at the output of XS4 about 2V. The frequency meter calibrates the GZCH scale. By setting the GZCH frequency to 1000 Hz and connecting an exemplary voltmeter to the XS4, calibrate the upper scale of the output meter by setting the maximum scale value to 1,8V. On the lower scale, 0% marks are applied against the 1V mark of the upper scale, 30% against the 1,3V mark, 60% against 1,6V. When using the meter for another value of the total shutdown current, it is necessary to change the value of C87 in parallel with the selection of R55 to maintain the same time constant. Next, turn off the GZCH. Temporary covers with holes are installed on the HF HRF unit to allow adjustment of inductance and capacitance trimmers. Turn on HGH. An oscilloscope (for example, C1-65A), with an input divider, checks the amplitude and shape of the signal on all subbands at the output of the VT4 source follower. If necessary, make a correction by changing the resistors R1 ... R5 within a small range. By applying +1V to XT12 with the help of a frequency meter (at the XW3 output), the boundaries of the subranges are laid. Then connect the oscilloscope to the RF output (XS1), set the attenuator to the "x100" position, the "mV" output control to the maximum and tune the resonant amplifier circuits as usual to the maximum. At the same time, the R92 trimmer maintains the output voltage within 50 ... 150 mV. It is also convenient to make the adjustment by turning on the GZCH, setting it to a frequency of 1000 Hz, and setting the modulation depth of 50 ... 70% with the GZCH output regulator. The moment of precise tuning of the amplifier is recorded by the maximum amplitude and minimum distortion of the envelope. Further on the frequency meter, a frequency of 1 MHz is set on the GSS. A high-frequency millivoltmeter with an input low-capacity divider, for example B1-1, is connected to the socket XS3 "X56" of the remote divider. The "mV" knob is set to a position close to the maximum. GZCH is turned off. The trimmer R92 is set to a millivoltmeter at the output of 100mV. Using the trimmer R86, set the output meter needle to "1V" (or 0% on the lower scale). Further, in exchange for temporary covers, permanent ones are installed on the RF block and soldered. The GSS is finally assembled and the front panel is installed (made of foil fiberglass, pasted over with black paper). Check all settings. Perform frequency calibration with a frequency meter. Next, the settings of R92 and R86 are checked, after which the scale of the RF output regulator "mV" is calibrated, marking divisions from 0 to 1mV through 0,1mV in accordance with the readings of an exemplary RF millivoltmeter. In the former case, all the inscriptions were made in white gouache with a drawing pen and a fountain pen. After that, the front panel was varnished twice PF-283. After drying the first coating, the pile is removed with fine sandpaper and the inscriptions are corrected. Literature
Author: S.Drobinoga, Poltava, Ukraine
Traffic noise delays the growth of chicks
06.05.2024 Wireless speaker Samsung Music Frame HW-LS60D
06.05.2024 A New Way to Control and Manipulate Optical Signals
05.05.2024
▪ Toshiba Dynabook R82 and Dynabook RT82 hybrid tablets ▪ VIPER26K regulators with built-in MOSFET 1050 V
▪ section of the site The most important scientific discoveries. Article selection ▪ article by Benjamin Disraeli. Famous aphorisms ▪ article When did you first use combs? Detailed answer ▪ article Mobile power station driver. Standard instruction on labor protection ▪ Cheese article. Simple recipes and tips
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page