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HEWLETT- PACKARD
JOURNAL
TECHNICAL INFORMATION FROM THE -hp- LABORATORIES
Vol. 9 No. 5
JBLISHED BY THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA JAN., 1958
An Automatic Noise Figure Meter
For Improving Microwave Device Performance
BECAUSE it compares actual output noise ment, a noise figure meter has been developed
power with the output noise power of a which both measures noise figure automati
theoretically ideal device, the quantity noise cally and has a number of important conven
figure is generally used to specify in a funda iences not previously available. The meter can
mental manner the quality of amplification be used with either 30- or 60-megacycle i-f re
SEE ALSO: provided in micro ceivers and has a primary measuring range
"Noise figure and wave devices such as from 3 to 30 db.
its measurement,"
r e c pe 3 i v e r s , f o r w a r d -
. The instrument is designed to operate with
wave and backward-wave tubes, etc. In addi gas discharge noise sources for measurements
tion to being a fundamental property, how on microwave devices and with temperature-
ever, noise figure can also be much faster and limited diodes for measurements on i-f ampli
easier to measure than equivalent measure fiers. A diode source and a series of high-per
ments with signal generators. From a perform formance waveguide noise sources have been
ance standpoint, improving receiver noise fig developed for these purposes. Supply voltages
ure in a system such as a radar is just as valuable for the sources are provided by the instrument.
and tremendously more economical than in The instrument provides two additional out
creasing transmitter power an equivalent puts for simplifying various measurements.
amount. A 5 db improvement in receiver noise One of these is a voltage that increases with the
figure, for example, is equivalent to increasing gain of the device being measured and is thus
transmitter power by 3:1. valuable in such work as adjusting twt's to the
To enable noise figure to be measured simply optimum gain region during the NF meas
and accurately and with economy of equip urement.
IK
Is
FREQUENCY (KMC)
Fig. 2. Recorded stcept NF measurement made of X-band
low-noise twt at General Electric Microwave Laboratory,
Palo Alto, using swept measurement techniques described
in text.
Fig. 1. (at left) -hp- Model 340 A Noise Figure Meter auto
matically measures noise figure of microwave receivers and
amplifiers over 3-30 db range and of 30- or 60-megacycle i-f
systems over 0 - 15 db range. Waveguide and i-f noise sources
have also been designed for these uses. NF meter outputs are
provided for recording swept measurements and for indicat
ing variations in gain of devices such as twt's.
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 8 H E W L E T T - P A C K A R D C O .