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Circuit Archives
Radio/ Oscillators
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High
Frequency Signal Generator
Reprinted with permission
from Rudolf Graf.
For this and over 1000 other electronic circuits, review and order Rudolf
Graf's Encyclopedia of Electronic Circuits on CD-ROM Vol-1
McGraw-Hill ISBN0078528119
FB19-17 |
Description: High Frequency Signal Generator
A tapped-coil Colpitts
oscillator is used at Q1 to provide four tuning ranges from 1.7 to 3.1 MHz, 3.0 to 5.6
MHz, 5.0 to 12 MHz and 11.5 to 31 MHz. A Zener diode (D2) is used at Q1 to lower the
operating voltage of the oscillator. A small value capacitor is used at C5 to ensure light
coupling to the tuned circuit. Q2 is a source-follower buffer stage. It helps to isolate
the oscillator from the generator-output load. The source of Q2 is broadly tuned by means
of RFC1. Energy from Q2 is routed to a fed-back, broadband class-A amplifier. A 2 dB
attenuator is used at the output of T1 to provide a 50 ohm termination for Q3 and to set
the generator-output impedance at 50 ohms. C16, C17 and RFC2 form a brute-force RF
decoupling network to keep the generator energy from radiating outside the box on the 12 V
supply. (QST, 1/86, p. 40.) From figure FB19-17 of Encyclopedia of Electronic
Circuits on CD-ROM Vol. 1. |
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