Phase lock reference provides a rapid and accurate method of determining the signal-to-noise ratio at the intermediate frequency stage of a receiver

Deerkoski, L. F.

English

NASA Technical Reports Server

May 1972	 B72-10102 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Signal to Noise Measurement Circuit 
	
AGC
	
Phase Lock 
	
Circuit	 Reference 
Input H	 Input	 f	 1MHz Signal	 Band Pass Filter 
The problem: 
At present there is no rapid and accurate method of 
determining the signal to noise ratio at the intermediate 
frequency of a receiver. 
The solution: 
A phase lock reference system provides a rapid and 
accurate method of determining the signal to noise ratio 
at the I. F. stage. 
How it's done: 
The circuit shown is a phase lock receiver with AGC 
control which maintains the signal level constant at the 
I.F. stage. This causes the noise to vary directly as the 
gain required to adjust the incoming signal level. By 
passing the I.F. signal plus noise through a limiter, the 
output signal from the limiter varies as a function of the 
I.F. noise level. The varying signal from the limiter is 
coherently detected since the input signals are phase 
locked to an internal reference. The phase lock reference 
mixing signal is clean; thus, the mixing process followed 
by a low pass filter gives a good measure of the varying 
signal level. This detected output is a measure of the in-
put noise level to the limiter. From this, signal to noise 
ratio at the I.F. can be determined. This technique has
Limiter
Low Pass	 Detected 
Filter	 Output 
application in providing optimum channel weighting in 
diversity receivers. 
Note: 
Requests for fUrther information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: B72-10102 
Patent status: 
This invention is owned by NASA, and a patent appli-
cation has been filed. Royalty-free, non-exclusive licenses 
for its commercial use will be granted by NASA. Inquiries 
concerning license rights should be made to NASA, 
Code 204-GSC, Washington, D.C., 20546. 
Source: L. F. Deerkoski 
Goddard Space Flight Center
(GSC-1 1239) 
Category 01 
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=19720000102 2020-03-17T03:25:01+00:00Z


Signal to noise measurement circuit

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