To configure receivers with narrowband FM modulation of an intermediate frequency from 5 to 21.4 MHz requires an oscillator with high frequency stability and internal (external) frequency modulation with small nonlinear distortion. Not all have industrial type generators G4-107 or G4-116. The proposed crystal oscillator, FM modulation may in some cases replace them. The oscillator circuit shown in Fig.1. At first glance, specifies the quartz oscillator is made on the VT3 transistor according to the scheme of capacitive treatacne (if it was not the coil L1). However, the inclusion of the expansion coil L1 scheme gives new properties - the ability to generate at a frequency below the frequency of the series resonance of the quartz. In this case, this scheme can be attributed to the scheme of the oscillator with a quartz resonator in the circuit.
In this scheme, the possible parasitic generation through the parallel capacitance of the resonator. For damping this generation is the resistor R12. The frequency control of the oscillator is not very usual. Vari-caps included as a capacitive divider, the emitter-base and emitter-collector of transistor VT3. With this inclusion of semiconductor capacitances frequency control according to the law, is close to linear, which is especially important for customroleprovider generator with small nonlinear distortion.
Generator low frequency oscillations made by the scheme with the rotation phase of the four-bar chain by a quadrupole, phasing voltage, and with a single stage amplifier transistor VT1. The frequency of oscillation is determined by the time constant of the two-port network and is equal to approximately 1 kHz. Low-frequency vibrations through the emitter follower to VT2 and the depth Adjuster deviation coming to the varactors. When using the resonator BQ 1 to 5 MHz frequency deviation is small, and if of 10.7 MHz quartz - quite sufficient for scoprono FM. With crystal oscillator via a broadband emitter follower high-frequency oscillations fed to the divider R23, R24.
(click to enlarge)
When using crystal resonator in the frequency 10700 kHz with a dynamic resistance of 30 Ohms, a voltage of high frequency oscillations at the output is 100 mV. Then they can further weaken the attenuator or to apply for a cascade of frequency multiplication. The multiplication of the frequency generator can be used as a calibrator FM radios. Thus, when the quartz resonator at a frequency of 12 MHz multiplying the frequency of the b signal is good is listening to a broadcast receiver (for example "Leningrad 010").
The scheme is going on PCB from one-sided foil fiberglass 1.5 mm thick. the Fee is designed to install the resistors MLT-0,125, ceramic capacitors type K10-17, electrolytic - type K50-35. Coil L1 wound on the frame with a diameter of 5.5 mm wire 0.1 mm in diameter and contains 20 turns. Trimpot core - type 30 HV Prho,7x8,0. Quartz resonator - type RK 169.
The location of the radioactive elements on the printed circuit Board shown in Fig.2, the arrangement of conductor paths on the reverse side of the circuit Board in Fig.3.
The development of stable generator is correctly set, the oscillation frequency of the podstroechnik coil L1. If spurious oscillations are not stable quartz resonator, includes a resistor R12 and choose its value from 470 Ohm to obtain harmonic oscillations of the desired frequency.
With a quartz resonator for a frequency of 10700 kHz with parallel capacitance pF 4,2, dynamic capacity 0,0172 pF and dynamic inductance 0,0128 MT was achieved sustainable generation when changing the supply voltage by 10%, and the inclusion of anti-parasitic resistor R12 is not required.
Authors: Oleg Belousov, I. chudaeva, Cherkassy region, Vatutino; Publication: N. Bolshakov, rf.atnn.ru