The setpoint generators, collected by mixing schemes, as well as tunable crystal oscillators were described several times before, but they are quite complex.
Offer simple master oscillator, the stability is almost equal to the quartz oscillator and does not require significant alterations in the case of application in a ready-made transmitter. The possible overlap of the frequency ranges of 400-500 kHz.
The principle of operation of the master oscillator is based on the following phenomenon. If in the quartz generator, assembled according to the scheme of capacitive "treatacne", to include in series with the resonator coil, the oscillation frequency decreases relative to the frequency of the quartz. If we turn on (also in series) capacitor, the frequency will increase. In both cases, the degree of change frequency will depend on the values of inductive (XL) and capacitive (XC) resistances. In this generator (see figure) in a chain of quartz is connected in series circuit L1C1. When the voltage resonance (XL=XC, and Z=0) the generator is operating near the frequency of the series resonance of the quartz. The capacitance change in either direction from the position of the resonance leads to a predominance of the influence of either capacitance or inductance.
To the frequency of the generator at maximum capacity after multiplication was equal to 144 MHz, it is necessary to use quartz with frequency corresponding to the harmonic 144,25-144,33 MHz (4010, 6015, 8020, 12030 kHz, etc.). Since many hams such crystals may not, you can use any quartz at 4, 6, 8, 12 MHz, reducing the layer of silver elastic band to obtain a resultant frequency 144,25 MHz. Note that with this increase in the frequency of a quartz activity and overlap somewhat reduced.
The variable capacitor C1 should have a maximum capacity of 100-150 pF and least possible value of the minimum capacity. The coil L1 has a diameter of 8-10 mm. in bulk and wound wire PELSHO of 0.15. The number of turns of 30-60 (depending on quartz). These coil L2 and the capacitor C2 depend on the frequency of the applied quartz and is therefore not indicated.
When establishing the generator install capacitor C1 to the maximum capacity. If a generation is missing, it is necessary to rewind a portion of the turns of the coil L1. If the generation fails in the minimum position of the capacitor C1, in parallel it is necessary to connect the DC capacitor 5-7 pF. To obtain the maximum overlap it is also useful to find the capacitance of capacitors C3 and C4.
The anode circuit L2C2 set to the appropriate harmonica. If you apply two or three switchable quartz, it is possible to block the part 144-145 MHz, which employs the vast majority of hams. If modifications are ready transmitter is sufficient to break the chain quartz to enable the circuit L1C1 and choose the parameters of the elements.
This device for several years successfully used RA6LAF, RA6LDC, UW6MA and UK6LAA.
Author: V. Gusinsky (UW6MA) Rostov-on-don; Publication: N. Bolshakov, rf.atnn.ru