Stable smooth range generator up to 30 MHz. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Stable smooth range generator up to 30 MHz. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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The generator provides stability (up to 30 MHz) sufficient for an amateur SSB transceiver. The generator circuit is shown in the figure.

Transistors V1 and V2 are connected in a common base circuit. The gain of the cascade on transistor V2 is close to unity, since its load is the low resistance of the emitter junction of transistor V1. The large collector junction resistance of transistor V2, included in the emitter circuit of transistor V1, creates a deep negative current feedback. Due to this, the output resistance of the cascade on the transistor V2 increases many times over and amounts to a few megaohms.

Such a high output impedance allows you to include the entire LC circuit in the collector circuit. A large load resistance allows you to get a high overall gain of the cascades (up to 1000) and establish a weak feedback (through the C4C6 divider), which reduces the effect on the emitter circuit of the transistor V2.

Stable smooth range generator up to 30 MHz

The output voltage is taken from the connection point of the transistors, low-resistance and well decoupled from the circuit. Therefore, the load has little effect on the generation frequency.

The generator used MLT-0,125 resistors, capacitors C3, C7, C8 - K10-7, C1 - KPVM-1, C2 - KSOT-1, C4 - KPK-MP. C6 - KD-2. C5 - CD-1.

For the frequency range of 28...29.7 MHz, a coil on an annular core of size K7x4x2 made of 7VCh ferrite was used. containing 9 turns of wire PELSHO 0.47.

The effective RF voltage at the output was 0,2 V. This voltage is sufficient to operate the mixer on germanium diodes. If the voltage needs to be increased, the D814A zener diode should be replaced with a higher stabilization voltage. An increase in the output voltage can also be obtained by reducing the resistance of the resistor R5.

After a ten-minute warm-up, the frequency drift of the generator (by 28 MHz) was 800 Hz for five minutes, and for the next five minutes - less than 100 Hz. After a half-hour warm-up, the generator frequency was in the range of inaudible beats for 10 minutes. In the absence of external electric and magnetic fields, the signal was almost sinusoidal.

Author: Y. Medinets (UB5UG), Kyiv; Publication: N. Bolshakov, rf.atnn.ru

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