Two or more series RLC circuits are used with a negative feedback amplifier to make a voltage variable oscillator. This combination results in high phase stability and optimum frequency modulation

Hearn, C. P.

English

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July 1965.	 Brief 65-10204 
NASA TECH BRIEF 
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NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
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Voltage Variable Oscillator Has High Phase Stability 
Bias	 Bias 
A	 A	 Negative Feedback 
L	 CV	 CV L 
HF- HE—	 V 
I F D3 
Modulating	
[Li Ics IR	 F Voltage C3 Tc, P 
The problem: Although frequency-modulated os-
cillators are available, their applications are restricted 
by certain operating limitations. In LC or reactance-
tube oscillators relatively low levels of phase stability 
are normal, and in piezoelectric crystal oscillators, 
modulation is limited to a fraction of a percent of the 
center frequency. 
The solution: A voltage variable oscillator using a 
low noise, phase stable amplifier with negative feed-
back, plus two (or more) series resonant LC circuits for 
high phase stability and optimum frequency deviation.
Amplifier negative feedback is accomplished by the 
network consisting of C3, Di, D2, and D3. A dc volt-
age proportional to the oscillator output voltage is de-
veloped across D3 and C3 and applied to the high-
frequency point contact diodes Di and D2. If the 
amplifier output tends to increase, the higher output 
signal reduces the dynamic. resistance of Di and D2 
and negative feedback to the amplifier increases to 
maintain a constant output signal level. 
Note: Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
How it's done: The resonant part of the oscillator	 Langley Research (enter 
consists of two identical series resonant circuits, each
	
Langley Station 
consisting of an inductor (L) and a voltage variable
	
Hampton, Virginia, 23365 
capacitance (Cv) loosely coupled by capacitor c2.
	
Reference: B65-10204 
Since C,, is a voltage variable capacitance, the oscil-
	
Patent status: NASA encourages the immediate 
lator frequency can be varied by applying a modulat-
	
commercial use of this invention. It is owned by 
ing voltage. A low-pass filter section, consisting of C,
	
NASA and inquiries about obtaining royalty-free 
Li, and C2, is used to isolate the RF oscillator signal 	 rights for its commercial use may be made to NASA, 
from the modulating signal. The filter load resistor R
	
Code AGP, Washington, D.C., 20546. 
has a resistance much greater than the capacitive re-
	
Source: Chase P. Hearn 
actance of C2 at the oscillation frequency.
	
	
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https://ntrs.nasa.gov/search.jsp?R=19650000202 2020-03-11T17:24:01+00:00Z


Voltage variable oscillator has high phase stability

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