4
Noise Source Selection
The other critical piece of equipment needed to make a noise figure measurement
is a noise source. Noise sources contribute to your total measurement noise
figure via ENR uncertainty and input mismatch.
The output of a noise source is defined in terms of its frequency range and excess
noise ratio (ENR). Nominal ENR values of 6 dB and 15 dB are commonly available.
A low ENR noise source will minimize error due to noise detector non-linearity.
This error will be smaller if the measurement is made over a smaller, and therefore
more linear, range of the instrument’s detector. A 6 dB noise source uses a smaller
detector range than a 15 dB noise source.
Use a 15 dB noise source for:
• General-purpose applications to measure noise figure up to 30 dB
• User-calibrating the fullest dynamic range of an instrument before measuring
high-gain devices
Use a 6 dB noise source for:
• Measuring a device with gain that is especially sensitive to changes in the
source impedance
• The device under test (DUT) has a very low noise figure
• The device noise figure does not exceed 15 dB
Agilent offers three different families of noise sources, and all may be used in
conjunction with the NFA. The smart noise sources simplify measurement set-up
and improve accuracy and reliability, automatically downloading electronically
stored calibration data to the instrument to save valuable time. The 346 Series
noise sources are the traditional and most cost-effective solution, offering the
widest range of frequency coverage. Lastly, Agilent offers high-frequency noise
sources for customers making measurements above 26.5 GHz. If one source does
not include both frequency ranges, a second source will be required. A second
noise source may also be necessary when measuring a non-frequency translating
device with low noise figure and high gain.
For more information on these noise sources see the Noise Figure Selection Guide,
literature number 5989-8056EN, or application note 57-3, “10 Hints for Making
Successful Noise Figure Measurements,” literature number 5980-0288E,
both available at www.agilent.com/find/nf.
Helpful tip: Agilent’s most
popular noise sources are the
N4000A smart noise sources and
346B traditional noise source.
Noise source ENR-typical Frequency range
N4000A 4.6 – 6.5 dB 10 MHz – 18 GHz
Smart Noise
N4001A 14 – 16 dB 10 MHz – 18 GHz
Sources
N4002A 12 – 17 dB 1 10 MHz – 26 GHz
346A 5 – 7 dB 10 MHz – 18 GHz
Traditional
346B 14 – 16 dB 10 MHz – 18 GHz
Noise Sources
346C 12 – 17 dB 10 MHz – 26 GHz
346CK01 21 dB 1 GHz – 50 GHz
High Frequency
Q347B 6 – 13 dB 33 GHz – 50 GHz
Noise Sources
R347B 10 – 13 dB 26.5 GHz – 40 GHz
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