
Model 8640B
TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-20. SINGLE SIDEBAND BROADBAND NOISE FLOOR (Cont'd)
2.
Set 10 dB step attenuator to 80 dB. Set reference signal generator for a 500.005 MHz (i.e., 5 kHz above the test
generator's frequency), CW signal at +13 dBm (output vernier maximum cw). Set 40 dB amplifier's input
impedance switch to 50 ohms.
3.
Set spectrum analyzer's resolution bandwidth to 1 kHz, set input level control to -40 dBm and dBm/dBV to dBm 50
ohm, and adjust frequency controls to set the 5 kHz difference frequency in the center of the display. Set
analyzer's display reference level controls for 10 dB per division with the 5 kHz difference signal 1.3 dB from the
top (reference) graticule line on the display.
NOTE
The correction factors for this measurement are as follows:
a. The DSB to SSB transfer is -3 dB because the mixing process translates two uncorrelated 1
kHz BW portions of the noise into the 1 kHz BW of the analyzer-giving
√
2 times the effective
noise voltage.
b. +2.5 dB because noise is average detected after logging.*
c. -0.8 dB. Effective noise BW is 1.2 x 3 dB BW which gives -0.8 dB - 10 log (actual 3 dB
BW/nominal 3 dB BW).*
Summing the correction factors gives -1.3 dB - 10 log (actual 3 dB BW/nominal 3 dB BW) or
approximately -1.3 dB ± 1 dB.
4.
Change reference signal generator's output frequency to 500.50 MHz. Set 10 dB step attenuator to 0 dB. Set
analyzer's display smoothing (video filter) to 10 Hz. The top graticule line on analyzer's display represents -110 dB
(the transfer from a 1 kHz BW to a 1 Hz BW is 30 dB). The average noise level on the display should be >30 dB
below the top graticule line (i.e.,>140 dB below carrier).
30 dB ___________________________
NOTE
If the test generator appears to be out of specification, check for excessive noise in the test
setup by disconnecting the test generator. The noise level on the analyzer's display should
decrease at least 10 dB.
* See Hewlett-Packard Application Note 150-4. Spectrum Analysis - Noise Measurements.
4-19
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