Quartz super oscillator (Super VXO). Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Quartz super oscillator (Super VXO). 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 proposed supergenerator differs from conventional quartz oscillators by using instead of one or two identical quartz resonators connected in parallel. This inclusion allows you to adjust the frequency of the generator in a much wider range than single-crystal circuits. So, according to my experiments for resonators at a frequency of 10,15 MHz, this range is about 40 kHz, and for 13 MHz quartz - about 90 kHz (!).

Quartz Super Oscillator (Super VXO)

The oscillator circuit was proposed by JA0AS (Mr. Shimizu) and JH1FCZ (Mr. Okubo) and named "Super VXO" by them. The first article about this generator was published in Japan in August 1980 in the magazine "Fancy Crazy Zippy" (N 64). Then this circuit was described in the book "Textbook for Homebrewing of Electronic Circuits" by JH1FCZ..

Here are the results of my experiments:

1. Two quartz crystals at a frequency of 10.15 MHz, a 15 μH inductor, a 20 pF variable capacitor. With these parameters, the generator worked in the range of 10.10 - 10.14 MHz. With such a generator, I made a direct conversion receiver for a range of 30 m. The frequency is very stable. A 2SC1815 transistor with an upper cutoff frequency of 80 MHz was used.

2. Two quartz crystals at a frequency of 13 MHz, an inductor VXO-50 (7 ... 11 μH), a 30 pF variable capacitor. The resulting tuning range is 12.91...13.00 MHz. The transistor is the same. The VXO-50 coil is proprietary, designed specifically for the VXO at 6 meters and has a small temperature coefficient.

I also used this generator in a QRP transmitter for 6 m. At a quartz frequency of 11.2735 MHz and after tripling, it covered the range of 50.00 - 50.27 MHz (270 kHz!).

The frequency range of tuning of the specified generator can be wider, but its stability becomes worse with increasing inductance. JH1FCZ recommends in his book to keep the frequency change within 0.5% of the rated frequency, i.e. for 10 MHz it is 50 kHz.

I have tried inductors of various designs, and as practice has shown, larger coils work better. When tuning the frequency, sudden frequency dips are possible, this can be eliminated by connecting in parallel the inductance of a resistor with a resistance of 10-30 kΩ.

Frequency stability depends largely on the temperature coefficient of the inductor core material used. Therefore, it is better to use coils without a core.

Author: MINOWA, Makoto, 7N3WVM; Translation and publication: N. Bolshakov, rf.atnn.ru

See other articles Section Knots of amateur radio equipment. Generators, heterodynes.

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