Radiometric receiver system, which measures noise temperatures in degrees Kelvin, does not require cryogenic noise sources for routine operation. It eliminates radiometer calibration errors associated with RF attenuation measurements. Calibrated noise source is required only for laboratory adjustment and calibration

Brown, W.

Ewen, H.

Haroules, G.

English

NASA Technical Reports Server

September 1970	 Brief 70-10376 
NASA TECH BRIEF 
--•-	 --- _____	 --	 - ---
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
-	 -- -----:-	 - ---------- --	 ______ 
Radiometric Absolute Noise-Temperature Measurement System 
Features Improved Accuracy and Calibration -Ease 
TE	
Jad
	 Chamber 
	
I	 _____ 
Switch	
Noise -
	 Reference 
Generator 
	
Generator	 Port (2)
SYNa
 I Modor1GET Detector Envelope H - Amplifier F[petec  
Coupler
c& Integra LuA;i; i r..® 
Switch 2
	
Noise Source	
L - - - -	
J [Load
	 Hfl Indicator TE  
Attenuator 
Port (1) 
Signal Input 
•	
Port 
Comparison' 
Port
rCalibration
Source 
LTL<_.J 
Reference Load
The problem:	 cryogenic noise sources for routine operation. This 
Standard radiometric methods for measuring the system eliminates radiometer calibration errors associ-
absolute temperature of microwave and millimeter ated with rf attenuation measurements. Output mdi-
noise sources require precise knowledge of rf attenua- cator zero position represents zero degrees Kelvin 
tion effects on instrument calibration. The measure- and the scale reads directly in degrees Kelvin. A cali-
ment of weak signals from low-noise-temperature brated noise source is required only for laboratory 
sources requires a resistive load immersed in liquid 	 adjustment and calibration. 
helium acting as a comparison noise source. These How it's done: 
methods require complex calibration procedures to
	 All rf components of the system (represented in 
ensure accurate measurements,	 the block diagram) are contained within an environ-
The solution:	 mental chamber at a temperature slightly higher than 
A new radiometric receiver system measures noise
	
the highest anticipated ambient operating condition. 
temperatures in degrees Kelvin and does not require 	 Connecting the comparison port of switch S I to a 
(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=19700000362 2020-03-17T00:44:58+00:00Z
reference load establishes the indicator-scale zero 
position. Introducing an external, calibrated noise 
source to the signal input port, then through port (1) 
to port (2), causes a negative indicator deflection 
proportional to the noise-temperature difference 
between the chamber and the calibration source. The 
relationship between the deflection in scale units and 
the noise-temperature differential provides a scale 
calibration in degrees Kelvin. Receiver calibration is 
completed by activating the noise generator and 
adjusting the attenuator to provide a positive indica-
tor deflection equivalent to the known absolute tem-
perature, TK. Switch S2 and noise source T C
 provide 
an independent measure of the noise level injected by 
the noise generator, attenuator, and coupler combina-
tion. 
The novelty of the system lies in (1) introducing 
switch S 1
 and the reference load to provide a zero-
position reading; (2) using a noise generator to provide 
an absolute calibration in degrees Kelvin; (3) using 
a noise source to monitor the radiometer; and (4) 
maintaining all critical rf components at a common, 
near-ambient temperature. These features combine 
to provide a highly accurate radiometer useful fr 
studying microwave emissions from the earth's surface 
and atmosphere; measuring atmospheric effects, 
plasma noise temperatures, and antenna-system 
noise temperatures; and in high-altitude radiometry 
of clear-air turbulence phenomena.
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-TR-R-27 1 (N67-35599), Absolute 
Temperature Measurement at Micro-
wave Frequencies 
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: G. Haroules, W. Brown of

Electronics Research Center

and H. Ewen of

Ewen Knight Corp.

under contract to

Electronics Research Center

(E RC-90066) 
Brief 70-10376	 Category 01


Radiometric absolute noise-temperature measurement system features improved accuracy and calibration ease

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