AM band adjustmentCascades of high frequency radio contain input circuits, and UHF frequency converter. The main objective when adjusting these cascades are checking LO generation and setting its contours, adjustment the gain stage higher frequency signals and the coupling configuration input circuits, UHF and LO.
Do not use a screwdriver for adjusting! A screwdrivers blade affects the tuning, but you need a non-metallic stick with a flat end.
Setting a begin check for generating local oscillator frequencies corresponding to each band. Verification is carried out using vacuum tube voltmeter and oscilloscope connected to the point of applying a voltage to the oscillator stage mixer (or transistor inverter in the performance of his single-transistor). The voltage to the local oscillator must be within certain limits, to create optimal conditions for the conversion stage. The values of these stresses are specified in the repair instructions and must be in the range of 100-200 mV. The shape of the local oscillator signal to be purely sinusoidal.
Verify that the local oscillator, start to set up its contours, the purpose of which is the correct styling range limits of the receiver. Overlapping oscillator frequency on each band should fall within specified limits of tolerance for frequency offset adjustment circuit when the temperature and humidity of the environment. Admission is 1-2% standard boundary frequency range.
When you configure the radios in the LW and SW, with internal magnetic antenna, the signal is fed from the generator of the standard fields, and in the range of KB, as well as setting up radios that do not have internal magnetic antenna, the signal is supplied from the GSS AM antenna via a standard equivalent. A tone modulated at 1000 Hz with a modulation depth of 30%. Tuning oscillator circuits are produced in the following order:
- Range switch is set to "DV". Variable capacitor set to the maximum capacity. Rotor tuning capacitor circuit oscillator range ET is set to the middle position. From the test generator serves AM signal with frequency 148 kHz, which corresponds to the lower end of the range with a small DV clearance. Rotate the tuning coil core contour LO ET tuned circuit on the maximum power output radio.
- Then the variable capacitor is set to the minimum capacity and give a signal to the upper frequency range of ET with a small tolerance (415 kHz). Trimmer tuned oscillator circuit so that the voltage at the output of the radio is maximized. Tuning in to the upper frequency range introduces some mismatch at the lower frequency. Therefore, GSS AM signal is fed back 148 kHz frequency, tuned to a receiver local oscillator and reset circuit trimming contour core coil. Then semi-variant capacitor oscillator circuit will adapt to the upper frequency range (415 kHz). Similar operations adjustment is repeated 2-3 times.
- Loop tuning range LO NE performed in a similar manner, serving successively boundary frequency range 515 and 1630 kHz.
After setting up the local oscillator circuits ranges LW and MW transferred to configure KB range. If the range of the radio KB panoramic, t. E. Covers the entire wavelength range from 25 to 75 meters, the limiting frequencies for frequency settings are: lower 3.8 MHz, 12.2 MHz upper. If the range is divided into SW half stretched out or expanded ranges, the frequency limits respectively are different.
When configuring KB circuits is very important not to make mistakes and to tune in to the signal of the main channel and not the mirror, the frequency of which lies above the ground on 930 kHz. To verify the correct placement of ranges SW frequency supplied from the signal generator is increased to 930 kHz. In this must be taken mirror signal.
Very often in the range of stacking KB boundaries performed only at the lower frequencies range and upper frequency limits only check for compliance with the required standards. They should be provided with face values applied in the condenser circuit.
After laying the range limits oscillator circuits carried adjustment circuits input circuits and UHF tuning by pairing them with appropriate local oscillator circuits. Pairing circuits can be started from any range if the input circuits do not have to connect an additional coils or capacitors. If, for example, the coil CB range are part of long-wave coils, the pair should begin with a range of ST.
Pairing circuits is carried out in reference points pairing. The lower frequency is usually chosen precise pairing 5-10% higher than the lowest frequency range, and upper - 2-5% below the maximum rate. For the lower frequency range NE interface is 570 kHz, the upper - 1560 kHz and average - 1000 kHz.
Setting circuits at lower frequencies bands performed Trimmer core contour coils, and on the top - tuning capacitor connected to the loop.
Setting (conjugation) of the input circuits LW and MW bands performed on a ferrite rod magnetic antenna, proceed as follows. Range switch is set to "NE". Alternator standard field signal is fed 1-3 mV lower frequency coupling (570 kHz) with a modulation frequency of 1000 Hz and a depth of 30%. The receiver is tuned to the frequency of the applied signal. Then, moving coil input circuit range NE along the ferrite rod antenna, adjust the input circuit on the maximum power at the output of the radio.
Displacement of the coil to the middle of the rod increases the inductance of the input circuit, the offset to the edge of the rod - decreases. The direction of movement is useful to determine with the help of the ferrite and copper rods, if the approach of the ferrite rod output voltage increases, the coil must be moved to the center, if the output voltage increases as the copper rod, coil must be moved to the edge of the magnetic antenna. If the approximation as ferrite and copper rods to the coil causes a decrease in the output voltage, then the coil circuit at a given frequency is tuned in resonance. During the configuration process, as we approach the fine-tuning the field strength of the applied signal should be reduced, since the large signal is difficult to accurately tune the receiver of the action of the AGC.
After pairing, at a frequency of 570 kHz generator rebuild ua upper frequency coupling (1550 kHz) and tune the radio to the frequency of the applied signal. Rotate the rotor tuning capacitor input circuit, achieve maximum voltage measurement at the output of the radio. Check the accuracy of the interface by presentation to the ferrite and copper rods. If for presentation ferrite rod output signal increases, increase the capacity of the tuning capacitor, and the output voltage increases when brought near a copper rod, the capacitance tuning capacitor should be reduced.
Pairing on the upper frequency can lead to disruption of conjugation in the lower frequency, so you need to make an adjustment to re-pair on the bottom, and then back to the top to get an accurate frequency pairing. After pairing, the input and LO circuits on the lower and upper frequencies of the input coil circuit is fixed on a ferrite rod antenna and move to the verification interface at the midpoint of the range, which is fed from the generator signal with a frequency of 1000 kHz. The receiver is tuned to the frequency of the applied signal and verify the accuracy of coupling in a similar manner. If the presentation to turn the ferrite and copper rods to the antenna coil output voltage will not increase more than 1.3 times, the setting can be considered satisfactory. Otherwise, you must replace the mating capacitor circuit; The desired capacitance of the capacitor can be determined in the following manner. If the presentation to the ferrite rod to the coil circuit input signal at the receiver output is increased, the capacity of a coupling capacitor should be increased. In the case where the output signal is increased approaching the input circuit of a copper rod, the capacitance of coupling capacitor needs to be reduced.
After replacing a coupling capacitor is necessary to re-execute the operation range of the local oscillator and laying hold a full cycle of conjugation. Bad pairing at the midpoint on all bands indicates malfunctioning of the variable capacitor.
After the setting range SV circuits go for pairing the input and LO circuits in the ET range.
Sequence of operations for configuring the range of DV is the same as when configuring the range of ST. The lower frequency range for precise pairing ET is 165 kHz, the upper - 380 kHz and average - 250 kHz.
Pairing settings radio circuits designed for operation from an outside antenna or whip antenna, exercise, feeding from GSS AM through its equivalent antenna signal to the radio. Alternately tuned circuits for each band radio. At lower frequencies, each band contours adjust the rotation of the contour trimming core coils, and at higher frequencies - Rotating trimmer capacitors. The adjustment is made to the maximum voltmeter readings included in the output of the radio.
Pairing and LO input circuits on the upper frequency leads to disruption of conjugation in the lower frequency, so for more accurate interface circuits tuning operation on the lower and upper frequencies of conjugation to repeat until no further increase in the output voltage "and will not provide the required sensitivity. the entire range. properly interfacing circuits attenuation image channel and the real sensitivity should not be worse than the norm for this type of radio.
After pairing, the circuit is tuned filter attenuation of signals with a frequency equal to the intermediate. For this purpose, the receiver is set to the position receiving a signal with a frequency which is closest to the intermediate (410 kHz, the upper end of the range LW) and with the oscillator signal is supplied with the frequency 465 kHz. Coil filter tuned to the minimum voltmeter at the output of the receiver.
After setup all trimmers cores contour coils provisions coils magnetic antenna lead wires to the SW antenna is intact.