HP 3048A Operating Manual page 84

Table 3-6. Setup Considerations for the Free-Running RF Oscillator Measurement Example.
Setup Considerations
Measurement Noise Floor
HP 8640B VCO Reference
Comments
The signal amplitude at the R input port on the HP 11848A sets
the measurement noise floor level. Use the following graph to
determine the amplitude required to provide a noise floor level
that is below the expected noise floor of your DUT. (The
Checking the Beatnote procedure in this section will provide you
with an opportunity to estimate the measurement noise floor
that your DUT will provide.)
L PORT LEVEL +15dBm
9 +15
m
TJ
_i
u
a
+s
_i
<
z
2 -5
to
a. o
O-
-140 -150 -160 -170 -180
EXPECTED PHASE NOISE FLOOR OF DUT (dBc/Hz)
f > lBKHz
If the output amplitude of your DUT is not sufficient to provide
an adequate measurement noise floor, it will be necessary to
insert a low noise amplifier between the DUT and the
HP 11848A input. (Refer to Inserting a Device in the Problem
Solving section of this chapter for details on determining the
effect that the amplifier's noise will have on the measured noise
floor.)
This uses the HP 8640B as the VCO reference source. In order
for the noise measurement results to accurately represent the
noise of the DUT, the noise level of the reference source should
be below the expected noise level of your DUT. If you have an
idea of the expected noise level of your device, you may want
to compare it to the noise characteristics graph shown for the
HP 8640B in the HP 3048A Reference Manual.
3-34 Signal Source Applications