Automatic gain control circuit for a radio receiver handles a wide range of input signal levels without overloading the output stage. The transistorized circuit maintains a relatively constant output by varying attenuation of the input signal

Black, S. H.

English

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March 1966	 Brief 66-10089 
00 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Automatic Gain Control Circuit Handles Wide Input Range 
Control Voltage	 —15 V 
The problem: 
Radio receivers that must handle a wide range of 
input signal levels must use some form of automatic 
gain control (AGC) to prevent overloading the final 
output stage. Presently available circuits are limited 
to maximum undistorted input signal strength of no 
more than 50 millivolts rms. 
The solution: 
An AGC circuit capable of handling input signals 
of the order of 1 volt rms. The transistorized circuit 
maintains a relatively constant output by varying at-
tenuation of the input signal.
How it's done: 
The input signal is coupled through Cl, to the var-
iable attenuator made up of diode tee-pad network 
CRi, CR2, and CR3. The attenuator is prebiased in 
the low-attenuation condition by a reference voltage 
coupled through rf chokes Li and L2. The attenuator 
control elements are Ri, C3, and Qi. Output of the at-
tenuator is coupled through C2 to reflex amplifier Q2. 
The amplified rf output is taken from resonant tank 
circuit L3-C6. The dc control voltage is fed : through 
blocking filter L4-C7 to the dc input of reflex ampli-
fier Q2. The amplified dc output voltage is developed 
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000089 2020-03-11T17:33:58+00:00Z
across collector load resistor R2 and is fed to attenua-
tor control transistor Qi. Emitter resistor R3, in con-
junction with R2 determines the dc gain of Q2, while 
C8, C4, and C5 act as ac bypass condensers to main-
tain the rf gain of Q2 as high as possible. 
Note: 
Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas, 77001 
Reference: B66-10089
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should be 
made to NASA, Code GP, Washington, D.C., 20546. 
Source: Stanley H. Black

of Sperry Gyroscope Company

under contract to

Manned Spacecraft Center

(MSC-166)
S 
S 
Brief 66-10089	 Category 01


Automatic gain control circuit handles wide input range

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