4-18. Checking and adjusting the channel selector
In most cases, the need to check the shape of the frequency characteristics and adjust the SC unit arises, for example, when the UHF circuits are detuned due to the displacement of the coil turns; when the capacitances of the circuits change when replacing lamps or transistors (due to the spread of their interelectrode capacitances); when the mounting containers are changed as a result of replacing parts during unit repair; when the intermediate frequency filter is detuned due to changes in the parameters of the tuned coil cores, etc. The adjustment of the SC unit should be done in the following order. First, the IF filter is adjusted, then the heterodyne circuits, the UHF bandpass filter, the input circuits, and finally the resulting frequency response is adjusted. It is advisable to first configure the SC block on one channel, and then configure the remaining channels in the same sequence. The setup should start from the twelfth channel. Let's consider setting up the SK block, carried out using the GKCH.
Rice. 4-5. Equivalent circuit with IF signal detector
Setting the intermediate frequency filter. The output high-frequency cable GKCh type XI-7 (divider in position 1:1) is connected through a capacitor with a capacity of 1000 pF to the control grid of the mixer lamp. The GKCH output can be connected directly to leg 2 of the mixer lamp using conductors or to the fourth contact plate of a large board. To do this, the side cover from the block is first removed. The input low-frequency cable of the GKCh is connected to the output of the S K block through an equivalent load, replacing the disconnected UPCH circuit. An equivalent circuit with an intermediate frequency signal detector is shown in Fig. 4-5.
While setting or checking the IF filter, the mixer grid circuit must be disconnected from its control grid. To do this, remove one of the heterodyne sectors from the block by placing the SK switch in the position in which this sector is turned on. The GKCh range switch is moved to position 27 - 60 MHz. By adjusting the corresponding knobs of the GKCh, one achieves obtaining on its screen the frequency characteristics of the IF filter of the SK block. The setting consists of changing the position of the IF filter cores in order to form a curve observed on the GKCh screen that corresponds to the reference one. In this case, they strive to obtain a two-humped curve with steep slopes, maximums of equal height and a minimal dip between them.
In blocks PTK-5, PTK-5/7, PTK-3 and PTK-10, the IF filter is adjusted by rotating the cores of coils Ll-61, Ll-62, L1-63, and in PTK.-ID - coils L1- 65. The L1-61 coil core, located on the lamp side, adjusts the right hump, and the L1-62 coil core adjusts the left hump of the frequency response. By rotating the core of the coil L1-61, the correct ratio of the levels of the outer humps is established.
Rice. 4-6. Frequency response of the IF filter of the SK block
At correct setting The hump contours must correspond to the intermediate frequencies of the image and audio signals, and the uniformity in the upper part of the characteristic should not exceed 10%. The distance between the humps, i.e. the bandwidth, should be 6.5 MHz. The required bandwidth is set by changing the magnitude of the connection between the circuits by slightly moving the movable cuff with the coil L1-61 and L1-62. Based on the obtained frequency response, one judges how the connection between the circuits needs to be changed so that the response has the desired shape. As the coils move closer together (increasing coupling between the circuits), the bandwidth becomes wider, and as the coils move away from each other, the bandwidth becomes narrower. After the connection has been changed, the coil cores are adjusted again. Once the adjustment is complete, the cuff is fixed to the frame using polystyrene glue or BF-4 glue.
The selection of the optimal connection between the circuits is made at the factory, therefore, when repairing the SC, it is necessary to resort to this operation only in the case of replacing the circuit. When properly configured, the frequency response of the IF filter has the shape shown in Fig. 4-6.
Setting and adjusting the heterodyne frequency. Setting up heterodyne circuits should begin with the highest frequency channel, and then proceed in descending order of channel numbers. The drum of the SK block is set to the receiving position of the tuned channel. In the PTK-5 and PTK-YUB units, the rotor of the local oscillator capacitor should be turned to the position corresponding to setting the local oscillator to the rated frequency (flat down), and in the PTK-5/7, PTK-7, PTK-3 and PTK-P units it is necessary to apply a voltage of about 5 V to the tuning diode (varicap).
If the UHF cascades are configured, then the high-frequency output cable of the GKCh (1:1 divider) is connected through a matching device (Fig. 4-7) to the input of the SK block, and the input of its oscilloscope is connected to the output of the SK block through an equivalent load tape. The TV image contrast control is set to the maximum gain position. Range switch GK 1! are moved to the position corresponding to viewing the frequency response of the channel being tuned. By rotating the GKCH knobs “Exit. voltage", "Gain U" and "Connected frequency" set the size of the frequency response convenient for observation.
If the UHF is not configured, then the high-frequency output cable of the GKCh is connected not to the antenna input, but to the control grid of the lamp of the first UHF stage, i.e., to the fourth terminal of the small contact board. The first and fourth contact plates of this board are connected during setup with a resistor with a resistance of 330 Ohms. Such a connection is necessary to eliminate the influence of the UHF grid circuit on the shape of the resulting frequency response. Then, by rotating the core of the heterodyne circuit, the nominal value of the local oscillator frequency for a given channel is set (Table 4-11). The image carrier mark should be located in the middle of the left slope of the frequency response. In this case, the core should not be in extreme positions. If, when tuning, the core has to be screwed in too deeply or by turning it it is impossible to set the image signal carrier to the middle of the slope of the frequency response, then you need to use a pointed stick of getinax to move apart the turns of the local oscillator coil. If the core protrudes from the frame, then you need to move the turns of the coil, after which the circuit is again adjusted with the core.
Rice. 4-7. Matching device for SK block with 75-ohm input
Table 4-11
Meaning of frequenciesf H 3. and G 3 V. UHF bandpass filter and local oscillator
Channel number | f from , MHz | f ZV . | Frequency tuning geter-homeland at f carried IF= =38 MHz | Channel number | f H4 ., MHz | f 3a .- | LO tuning frequencies at fcarried IF= -38 MHz |
To provide access to the coil turns of the tunable sector, the two heterodyne sectors following it counterclockwise are removed. When determining the direction, the drum is looked at from the long end of the axis. When the circuit is adjusted, it is necessary to secure the coil turns with glue and check the setting again. If the local oscillator is configured correctly, then the vertical line of the instrument’s scale grid, corresponding to the carrier intermediate frequency of the image, intersects the left slope of the curve at a level of 0.5 of the frequency response. When turning the “Settings” knob, the intersection point should move symmetrically relative to the 0.5 level of the characteristic.
If there is a slight deviation of the local oscillator frequency from the nominal value, adjustment can be made (for example, PTK-YUB) while receiving a television program. To do this, switch the unit to the required channel, set the local oscillator tuning knob to the middle position, and insert a long narrow screwdriver into the hole located near the rotor of the local oscillator trimming capacitor and turn the local oscillator core 1/3 of a turn in one direction or the other. In this case, the core should not protrude from the sector or be recessed to a depth of more than 4 mm. This corresponds to approximately five full rotations of the core. Then the screwdriver is removed and the local oscillator adjustment knob is used to check the setting. If the adjustment does not give the desired result, then the adjustment is repeated.
Setting up a UHF bandpass filter. To obtain the characteristics of a bandpass filter on the GKCh screen, it is necessary to connect a high-frequency cable (1:1 divider) to the input of the block, a low-frequency cable - in the PTK-YUB, PTK-N blocks - to the control point KT-1, and in the PTK-3 block to the third plate of the fixed board of the contact group of the heterodyne sector. The GCH range switch is set to the corresponding range, and the switch in the channel selector is set to the channel being tested.
Using the GKH adjustment knobs, the dimensions of the curve are convenient for observation. The required shape of the frequency response of a UHF bandpass filter is shown in Fig. 4-8. The gap between the humps on the characteristic should be within 30 - 50% of the height of the left hump. Frequency values! from. and f 3B., on which the humps of the frequency response of the bandpass filter should be located, are given in table. 4-12. The shape of the frequency response depends on the inductance value of the anode and grid windings, the degree of coupling between them, the capacitance of capacitors C1-6, C1-10 and the distributed capacitance of the installation and lamps. If the frequency response obtained on the GKCh screen differs from that shown in Fig. 4-8, then it is necessary to adjust the UHF bandpass filter. The bottom cover of the unit is removed and, for ease of adjustment, two or three heterodyne sectors located next to the sector of the channel being tuned are removed.
Rice. 4-8. Frequency response of a UHF band-pass filter
UHF circuits are adjusted by moving the turns of the coils with a pointed insulating stick. To expand the filter's bandwidth, you need to move the coils towards each other; to narrow the bandwidth, they are moved apart. To align the curve humps, it is necessary to move the outer turns of the coil. When the curve shifts towards low frequencies, the outer turns of the anode and grid coils should be moved apart. After adjusting the bandpass filter, the turns of the coils are secured with a thin layer of polystyrene glue or BF-4 glue. It should be remembered that the capacitances of the trimming capacitors C1-6 and C1-10 are installed when setting up the bandpass filter on the 10th - 12th television channels, since by moving the turns of the coils of these channels, consisting of only 2 - 3 turns, adjustment can only be made with a certain capacitance of the tuning capacitors. When tuning other channels, it is not recommended to rotate tuning capacitors C1-6 and C1-10.
Setting up input circuits. To configure the input circuits, the high-frequency cable of the GKCh with a 1: 1 divider remains connected to the channel selector input through matching device, and the low-frequency cable is connected through the load equivalent and the detector head to the output of the tuned unit. The block is switched to the channel being tested. The local oscillator “tuning” knob is set to the position corresponding to the average frequency of the local oscillator. The tuning is carried out in the same sequence as for heterodyne circuits, i.e. starting with the highest frequency channel.
Begin tuning by rotating the brass core of the antenna sector. To access it, there is a hole in the block body on the side of the short axis. The core must be rotated slowly, since the permissible depth of core movement is the same as when setting up heterodyne circuits. When setting up, they achieve on the GCH screen a double-humped curve with an unevenness in the upper section of no more than 10 - 15% (on the first five channels) and 25 - 30% (on the 6th - 12th channels). The frequencies at which the curve humps are located should not differ from the values ! short circuit . and f 3B., indicated in table. 4-11. Deviations are allowed no more than 0.5 MHz in the direction of narrowing and no more than 1.0 MHz in the direction of expansion.
To raise the right hump of the characteristic, the core must be screwed into the coil frame, and to lift the left one, it must be unscrewed. If adjusting the core fails to achieve the desired result, then adjustment is carried out by moving the turns of the coils. For this purpose, it is necessary to remove the bottom cover of the unit and remove two or three antenna sectors located next to the sector of the channel being tuned. If the right hump of the frequency response is higher than the left one, then the turns of the grid coil should be moved to the middle, and if the left one is higher, then they should be moved apart to the edges of the frame. If the frequency response has a hump in the middle part, then you need to spread the turns of the antenna coil over the mesh coil equally in both directions. In this case, the left hump increases, which is reduced by moving apart the turns of the grid circuit coil. If the characteristic in the middle part has a large dip, then the turns of the grid coil are moved apart from its middle into two sections, and the turns of the antenna coil are connected together.
Rice. 4-9. Frequency response of the IF signal suppression circuit
Rice. 4-10. The resulting frequency response of the SC block
Setting up the IF signal suppression circuit. In this case, the RCC is connected in the same way as when setting up an IF filter. GKCH handles “Exit. voltage" and "Gain U" are set to the position corresponding to the maximum output signal. Use the “Scale” and “Medium Frequency” knobs to display frequency marks 37, 38, 39 MHz in the center of the screen. By stretching or compressing the turns of the L1-64 coil (in the PTK-3, PTK-YUB block or rotating the core of the PTK-P coil), ensure that the notch mark is located on the characteristic at a frequency of 36 MHz, as shown in Fig. 4-9. After setting up the PTK-3 and PTK-YUB blocks, you need to seal the coil turns with polystyrene glue or BF-4 glue.
Checking the resulting (end-to-end) characteristics of the SK block. The last step in setting up the channel selector is to check its end-to-end characteristics. To do this, the output of the GKCh (divider 1:1) is connected to the antenna input of the unit through a matching device (see Fig. 4-7), and the input of the oscilloscope is connected to the anode of the lamp with a cable with a detector head through a capacitor with a capacity of 100 - 200 pF first cascade of UPCH. The anode circuit of this lamp is shunted with a resistor with a resistance of 200 - 300 Ohms. The “Setting” knob of the local oscillator (in the PTK-YUB block) is set to the middle position, and its switch is set to the channel being tested.
By adjusting the GKCH knobs “Out. voltage", "Gain V" and "Average frequency" (without overloading the device) ensure that the frequency response of the channel being tested is displayed on the screen. For a correctly configured block, the resulting characteristic should be located in the shaded area (as shown in Figure 4-10). If the frequency response of the channel being tested does not fit within the established tolerances, then its final formation is carried out by adjusting the input circuit. Sometimes you need to check the settings of the IF filter and UHF bandpass filter.
4-19. Setting up and checking the UPCH
Before starting the setup, it is necessary to disconnect the SK unit, the deflection system (OS), remove the socket from the kinescope base and connect points 49 and 50 located on the UPCH board.
The setup begins with the third cascade of the UPCH. First, the anode of the L302 lamp must be connected to the chassis through a capacitor with a capacity of 2200 pF or the anode circuit L306, L307 must be bypassed with a 200 Ohm resistor. Otherwise, a small “dip” will be visible in the middle of the frequency response. The output high-frequency cable of the GKCh with a 1: 1 divider is connected to the control grid of the LZOZ lamp (control point KT-7), and the input of its oscilloscope is connected through a resistor with a resistance of 47 kOhm to the load of the video detector (control point KT-8). The device sweep frequency switch is set to the “MHz Ranges” position, and the range switch is set to the “27 - 60” MHz position. At correct installation the remaining knobs of the device and when rotating the “Average Frequency” knob, the resonant curve of the F305 filter should appear on the device screen, which is installed in the center of the screen, shifting it horizontally with the “Medium Frequency” knob. Use the “Scale” knob to set this width of the resonance curve, and use the “Gain U” and “Output” knobs. voltage" such a height that the shape of the curve corresponds to that shown in Fig. 4-11. If necessary, rotate the cores of the coils L312, L313 so that the peaks of the curve are at frequencies of 32 - 32.5 and 38 MHz. Then disconnect the capacitor from the anode of the L302 lamp or the resistor that shunts the anode circuit.
Rice. 4-11. Frequency response of the third stage
Rice. 4-12. View of the characteristic section after setting up the contoursL310AndL311
Rice. 4-13 Symmetrical resonance curve with a maximum at 35 MHz
When setting up the second and third stages, the output of the GKCh is connected through a divider I: 1 to the control grid of the L302 lamp (control point KT-5). The input of the GKCh device remains connected to the KT-8 control point. To eliminate the influence of the L301 C308 circuit on the image of the frequency characteristics of the second and third cascades, it is necessary to short-circuit the anode of the L301 lamp of the first cascade with a 2200 pF capacitor on the chassis or bypass the anode circuit with a 200 Ohm resistor. Using the GKH control knobs on the device screen, the image is set in such a way that the section of the curve with frequencies of 29 and 31 MHz is clearly reproduced in the center. By rotating the core of circuits L310 and L311, they achieve a minimum at a frequency of 30 MHz (Fig. 4-12). Then, having set the image size convenient for observation by alternately rotating the cores of the coils L307 and L309, they achieve a symmetrical curve with a maximum at a frequency of 35.5 MHz (Fig. 4-13). The bandwidth of the frequency response is set by the core of the coupling coils L306 and L308. After tuning, it is necessary to disconnect the capacitor or resistor shunting the anode circuit from the L301 lamp.
Setting up notch circuits. The output of the GKCh device is connected through a 1:10 divider to the control grid of the L301 lamp (control point KT-4 or socket 8 of the KP-la panel). The oscilloscope input remains connected to the video detector load (test point KT-8). Using the GKCH “Exit” knobs. voltage", "Gain V", "Scale" and "Average frequency" maximize the image and shift the section of the curve at frequencies 39 - 40 MHz to the center. By rotating the core of the L303 coil, the notch notch is set to a frequency of 39.5 MHz (Fig. 4-14) and by rotating the variable resistor R308, its greatest depth is obtained. After this, a section of the curve at frequencies of 30 - 32 MHz is shifted to the center of the GKCh screen and by rotating the core of the L305 coil, the gain is reduced at a frequency of 31.5 MHz (Fig. 4-15). Then check the position of the notch at a frequency of 30 MHz, if necessary, adjust by rotating the core of the communication coils L310 and L311.
Figure 4-14 View of the characteristic section at the notch point 39.5 MHz
Figure 4-15. Frequency characteristics at the point of rejection of the sound carrier of the received channel 31.5 MHz
Setting up the first cascade of the UPCH. To do this, the low-frequency input cable of the oscilloscope, at the end of which there is a detector head, shunted with a resistor of 150 - 300 Ohms, is connected through a capacitor with a capacity of 100 - 300 pF to the anode of the L302 lamp (leg 5). The high-frequency output of the GKCh device remains connected to the control point KT-4 Regulator “Out. voltage" is set to a position corresponding to approximately 1/3 of the full output voltage (to avoid distortion of the frequency response due to limitation). Using the "Gain U" regulator, it is necessary to set the full range of the frequency response on the device screen. By rotating the cores of coils L301 and L304, you should obtain the frequency response shape shown in Figure 4-16. Its peaks should be located at frequencies of 33 and 37 MHz.
Information book L 1979 Gruev, I.D. ... Lepaev, D.A. Repair household electrical appliances, electric players and..., V.D. Inspection and testing radio equipment M 1970 Manovtsev, A.P. ...
2.3.1. By analogy with the first works, create a time diagram file labor3.scf in the project folder D:\users\group number\Sidorov and set the simulation time to 2 μs.
2.3.2. By analogy with clause 2.3.2 and clause 2.3.3 of the second laboratory work, move the file labor_adc1. scf into the labor3.scf file window already formed timing diagrams of the input signals CLC, AEN, SA addresses and the high part of the SA register addresses on the address bus, as well as the output signal of the SEL adapter in the state at the beginning of the simulation.
2.3.3. Launch the simulator. The resulting timing diagram for the SEL signal should correspond to Fig. 3.
2.3.4. After completing the steps in paragraph 2.3.5 of the second work, make changes to the selector macro circuit, setting it up to select register addresses corresponding to the task variant. Compile the modified selector circuit and, if compilation is successful, close the macro circuit.
2.3.5. Open the labor3.scf timing diagram file window. and replace on the SA bus the addresses 2CC, 2CE, 2CD and 2CF of the ODR, CR, IDR and SR registers with the addresses of these registers in accordance with the option for setting table. 1.
2.3.6. Launch the simulator. If the address selector is correctly configured and addresses are set on the SA bus according to clause 2.3.4 and clause 2.3.5, respectively, the timing diagram for the SEL signal will correspond to Fig. 3, but with the values of the register addresses on the address bus corresponding to the job option.
2.4. Modeling and tuning of the control signal generator
2.4.1. By analogy with paragraph 2.4.1 of the second work, make changes to the FUS circuit, setting it up for a given task option. Compile the modified fus2 macro schema and, if compilation is successful, close it.
2.4.2. By analogy with clause 2.4.2 and clause 2.4.3 of the second laboratory work, replace the timing diagrams in the labor3.scf file window with diagrams from the labor_fus2 window. scf. The screen will display already formed timing diagrams of input signals CLC, AEN, NIOW, NIOR, SA0, SA1, address codes of registers on the SA address system bus, as well as output signals WOR, RSR, WCR and RIR of the adapter in the state at the beginning of the simulation. Make changes to the register address code diagram on the SA bus, replacing addresses 2СС, 2CD and 2CE and 2CF with the addresses to which the ADC was configured.
2.4.3. Launch the simulator. If the FUS is configured correctly and the addresses on the SA bus are set correctly, the timing diagram for the SEL signal and the control signals WOR, WCR, RSR and RIR will correspond to Fig. 5, but with the values of the register address codes on the address bus corresponding to the job option.
2.5. Simulation of adapter operation
When organizing interaction with the control panel in interrupt mode, the processor (driver program) must configure the control panel adapter to operate in this mode. To do this, it performs a cycle of writing to the CR control register of byte D7-D0, in which bit D1 must have the value 1. The high level signal of bit D1 = 1, arriving via line SD1 of the SD ISA data bus to the input of trigger T3 of the CR control register, will ensure the formation at its output Q1 the interrupt enable signal INTA, and, therefore, with IF = 1 and the interrupt request signal IRQ at the output of the AND2 matching circuit.
The single value of the SD0 bit, the signal of which is supplied via the SD0 line to the input D of the T2 trigger of the CR register, as in the adapters of the first two works, is used to generate the Start signal.
The cycles of writing a byte (AD) to the output register ODR of the adapter to set the argument and byte 03h (D0=D1=1, the remaining bits of the byte are zero) to the control register CR to generate the INTE and Start signals are shown in Fig. 7. The diagrams are shown for an adapter developed according to the “example” option.
After setting the argument for the PU, the type of exchange with it and its launch, the processor will continue executing commands of the interrupted program that are not related to accessing the IDR register of the adapter. In the timing diagrams shown in Fig. 7, these are commands for reading data from ports with addresses 3BBh, 3BAh and 3B9h.
The IRQ interrupt request signal, which appeared at the output of the adapter when the bit or ready flag IF=1 was set in the SR status register, will be sent via one of the IRQi lines of the SC control bus of the ISA bus to the input of the programmable interrupt controller PKP of the processor module. The control panel will generate an INT interrupt signal and send it via a special line to the maskable interrupt INTR input of the processor.
Upon the INT signal, the processor must complete the execution of the command of the interrupted program, which received the IRQ interrupt request signal (in Fig. 7, this is one of the commands for reading data from ports with addresses 3BBh, 3BAh, 3B9h), and proceed to the execution of the interrupt service procedure. The result of this procedure should be the processor executing a command to read data from the data register of the adapter that requested the interrupt - in our case, from the input data register IDR.
2.5.1. Set the simulation time to 1.7 μs and, by analogy with clause 2.4.2, replace the timing diagrams in the labor3.scf file window with the timing diagrams from the labor_r3_in file window. scf. The screen will display the already generated timing diagrams of input signals and codes shown in Fig. 7, as well as the output signals SEL, WOR, ROR, RIR, STB, WCR, PUSK and data on the PUD, ID, OD, SD(O) buses of the adapter in the state at the beginning of the simulation.
2
.5.2. Make changes to the register address code diagram on the SA bus, replacing addresses 2СС, 2CD and 2CE and 2CF with the addresses to which ADC and FUS were configured. Replace the data byte (ADh) on the SD(I) data bus with the code from the “Argument” column of the table. 1, corresponding to the task option.
2.5.3. Launch the simulator. The timing diagrams of output signals and codes on the adapter buses must correspond to Fig. 8, but with register addresses and “Argument” corresponding to the task option.
2.5.4. Set the simulation time to 4.0 µs. Continue the simulation by making changes to the diagram of codes on the SA bus and signals on the NIOR line so that the processor, executing the interrupt service procedure, executes a cycle of the command to read data from the input register IDR of the adapter after time T = K*100 ns after completion of the command, at which the IRQ signal appeared at the adapter output (read at address 3BAh),
The time period T was introduced to simulate the time required for the processor to find the interrupt procedure using the control panel and execute the commands of this procedure preceding the read command from the IDR register (see lecture course). For even variants of tasks, take K equal to one, for odd ones - two.
2.5.5. Launch the simulator. Save the resulting time diagrams under the name labor_r3_out1. scf and include it in the report.
2.5.6. After completing the reading cycle from the IDR register, continue simulating the operation of the adapter in the ready exchange mode, disabling the adapter exchange by interruption. To do this, make changes to the code diagrams on the SA address buses, SD data and signals on the NIOW and NIOR lines, ensuring sequential execution by the processor:
1. A cycle of the command to write a new argument to the ODR register, which would be 33h less than the one specified by the job option;
2. Cycle of the command to write to the control register CR byte 01h, which ensures the launch of the control unit and the prohibition of exchange by interruption;
3. Several cycles of commands to read data from the SR status register in order to check the status of the IF ready flag.
2.5.7. Launch the simulator. Using the resulting diagrams, determine the reading cycle from the SR status register, during which code 01h appeared on the SD(O) data bus, indicating that the readiness bit IF=1 was set in the register.
2.5.8. Make changes to the diagram of codes on the SA bus and the signal on the NIOR line, ensuring that the processor cycle executes the command to read data from the input register IDR of the adapter after the read command from the SR register, where code 01h appeared on the SD(O) bus.
2
.5.9 Launch the simulator. Save the resulting time diagrams under the name labor_r3_out2. scf and include it in the report. Timing diagrams of input and output signals and codes on the buses listed in clause 2.5.1 for the adapter developed according to the “Example” option with K = 3 are shown in Fig. 9.
Adjusting the selector includes the following operations: checking and adjusting the frequency response of the radio frequency amplifier and local oscillator, adjusting the IF input circuit.
Checking and adjusting the frequency response of the frequency amplifier and local oscillator. The connection diagram for measuring equipment is shown in Fig. 17.
A voltage signal of about 10 mV is supplied to the selector input from the frequency response meter TR-0813 (X1-50) using a coaxial cable. From the selector, the signal is taken from the KT2 control point using a cable with a detector head, shunted by a 75 Ohm resistor, and then fed to the frequency response input. A voltage with a frequency of 38 MHz is supplied to the “IF output” of the selector from the radio frequency generator at a level convenient for observing the mark on the frequency response screen when tuning the local oscillator. The amplitude-frequency response of the tuned selector should be located in the shaded area.
Rice. 17. Block diagram of connecting devices for configuration
Frequency response of the radio frequency amplifier and local oscillator of the channel selector
SK-M-24-2 (a) and frequency response form (b)
When adjusting the frequency response of a radio frequency amplifier, you must be guided by the following provisions:
spreading the turns of coils L12, L15, L13 and L16 reduces the inductance of the circuits and shifts the adjustable characteristic towards a more high frequencies(to the right on the frequency response screen);
compression of the turns of coils L12, L15, L13 and L16 increases the inductance of the circuits and shifts the characteristic towards lower frequencies (to the left in the frequency response);
increasing the distance between coils L12 and L15 or reducing the inductance of coil L14 (ranges I, II) reduces the coupling between them and allows the frequency response of the radio frequency amplifier to be narrowed;
decreasing the distance between the loop coils L12 and L15 or increasing the inductance of the L14 coil increases the coupling and expands the frequency response of the radio frequency amplifier;
reducing the distance between the secondary loop coil L15 (or L16) and the corresponding coupling coil L17 (or L18) narrows the frequency response, reduces its dip and vice versa;
a decrease in the inductance of only the moving coils L12, L13, with the connection between the loop coils remaining unchanged, leads to a slight increase in the right maximum frequency response of the radio frequency amplifier and shifts it towards higher frequencies;
increasing the inductance of only the secondary coils L15 and L16, with the connection between the coils remaining unchanged, allows you to significantly increase the left maximum frequency response of the radio frequency amplifier and shift it towards lower frequencies.
The channel selector is first adjusted in ranges I-II from channel 5, setting the adjustment voltage to 20V on pin 4 of connector X1. Tuning in the III range begins with channel 12, setting the tuning voltage to 18V on pin 4 of connector X1. When setting up these channels, the maximum frequency response of the radio frequency amplifier must be located symmetrically relative to the carrier frequencies of the image and sound of the corresponding channel, and the frequency is determined by the marker marks of the frequency response.
If necessary, adjustment is made using tuning capacitors C24, C27 on ranges I-II and C19, C28 on range III. When adjusting the selector with wire capacitors (C8, C11, C24, C26), the change in capacitance is achieved by changing the number of turns. The capacity decreases as the turns are unwinded, and the remaining output is bitten off.
Next, it is necessary to adjust the local oscillator frequency by combining ff, from with f from on the observed frequency response. To do this, by moving or compressing the turns of coil L19 (range III) on channel 12 and coil L20 (ranges I-II) on channel 5, align the mark ff, from with f from on the observed frequency response. After adjusting the local oscillator frequency, coils L19 and L20 are no longer adjusted.
By changing the voltage on pin 4 of connector X1 in range III, they are tuned to channel 6, and in ranges I-II - to channel 1. When tuning these channels, the frequency response maxima of the radio frequency amplifier should be located symmetrically relative to fiz and fz, and the mark ff,iz should be aligned with the mark fiz. If necessary, adjust the frequency using coils L12, L15, L17 in range III or coils L13, L14, L16, L18 in ranges I-II. The voltages on pin 4 of connector X1, at which the adjustment is made, must be recorded, since these voltages must be set when checking the unevenness of the frequency response after repair.
Setting up the output circuit of the inverter. Structural scheme Connections of devices for this type of work are shown in Fig. 18.
A signal with a voltage of about 10 mV is supplied to the selector input using a radio frequency cable from the frequency response. The IF signal from the selector output is fed to the frequency response input using a cable with a detector head shunted with a resistance of 75 Ohm. Then connect the voltage to the corresponding contacts of the selector connector when operating in range III. By changing the voltage on pin 4 of connector X1, adjust the selector to one of the channels of the III range. Using the core of the inductor L21, the peak of the maximum frequency response curve is adjusted to the average intermediate frequency of 34.75 MHz.
Rice. 18. Block diagram of connecting devices for configuration
input circuit of the IF channel selector SK-M-24-2
In this article we will look at the different types of selectors. Each of them has its own task and each works only if conditions are met, and according to these conditions they are divided into several types:
1) Regular selector.
2) Context selector.
3) ID selector.
4) CLASS selector.
5) Parameter selector.
Discuss regular selector we won’t, because, firstly, we discussed it, and, secondly, it’s ordinary HTML tag, so there’s nothing to say here.
Now let's look at it in detail context selectors, since they are used, perhaps, most often. They are needed so that a style can be applied to an element, provided that this element lies inside a tag that lies inside another tag. It sounds confusing, I don’t argue, but let’s understand it with an example
Header in container
Element, in in this case- this is the text " header in container" lies in the tag Tag1 tag2 ( And it works like this: if tag2 is inside tag 1, then the elements inside tag2 will accept properties1 And properties2 with meanings value1 And value2. And now an example CSS for the example above. Div h2 ( This style will be applied to the example above and " header in container" will become bold. And if it is written simply: Then the style will not be applied to this element, because it is not inside the tag Question: what are they for? context selectors? You will be forced to use them repeatedly, due to the fact that your page will probably have many duplicate tags (
, ID selectors are also very common. They allow you to specify a unique element on the page, and the syntax for declaring this selector is as follows: Tagname#name ( Now if the tag " tag name"has attribute" id"with meaning" Name"then to the elements inside the tag " tag name" the style will be applied. If " tag name" is missing (that is, the selector begins with the character "#"), then this style can be applied to any tags that have the attribute " id" in meaning " Name". And now an example: #red ( And now HTML code, to which this style will be applied: Red text As you can see, everything is very simple, but there is one big BUT! Use ONE ID only ONCE per page! For example, you can’t write like this: Red text Another red text In such cases, you need to create two identifiers like this: #red1, #red2 ( AND HTML code: Red text Another red text Now it will be right. By the way, pay attention to the “comma” in the selector description. This is a common technique for reducing the number of lines in a style. If you have two or more elements with the same style, then you can list all the selectors separated by commas, and then write the corresponding style for all of them at once, as in the example above. Now about selector CLASS. He is very similar to ID selector, but its "name" can be used multiple times on a page. The general syntax for this selector is as follows: TagName.name ( Thus, if the tag " tag name"worth attribute" class"with meaning" Name", then this style will be applied to the elements inside. Likewise, with ID selector, If " tag name" is not specified (that is, the selector description begins with the symbol "."), then this style can be assigned to any elements. And now an example: Red ( AND HTML code for this style: Red text Another red text Again, everything is very simple. Now the question arises: what is better then? ID selector? And it is better in that these elements are very convenient to access through, for example, JavaScript. Therefore, it is very convenient to specify exactly ID, provided that there is only one such element on the page, that is, it is unique. And the last type CSS selectors
- This parameter selector. Not used very often, but in some cases it is almost irreplaceable. I hope you noticed that the appearance of many tags depends on their attributes. A striking example is the tag
, which can be a button, a radio button, or a text field. Agree that all these elements look completely different, however, the same tag is responsible for them. And in order to apply the style only when a certain value any attribute, and use parameter selectors. The syntax is as follows TagName[attributename="attributevalue"] ( This style is applied in the following case: if in the tag "name" the value of "attributename" is equal to "attribute value" then the style will be applied, otherwise the style will not be applied. To make it even clearer, I give an example: Input ( AND HTML: I hope that everything is transparent here too. Another very important point, kinds selectors you can combine, for example, this CSS quite normal and working: #header li a ( AND HTML code which will call this style: I think that there will be no questions here either. Finally, I would like to say that selectors- this is something that anyone who knows must know. How to use these selectors- it depends only on your design skills.
, which in turn lies in the tag
property1: value1;
property2: value2;
}
font-weight: bold;
} Heading
,
,
and others), and, of course, you will want them to not always have the same appearance. And this is where they will come to the rescue context selectors.
property1: value1;
property2: value2;
}
color:red;
}
color:red;
}
property1: value1;
property2: value2;
}
color:red;
}
property1: value1;
property2: value2;
}
border: 2px double black;
}
font-size: 150%;
}