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RF
Power and
TRFL
5-11
Noisy Source
Diagram 5-4 shows how to set-up
TRFL
measurements for an
extremely noisy signal source. Using
t h i s
setup, signal levels with
many M H z of residual FM deviation can be measured to -100 dBm.
Diagram
5-4.
Setup for Measuring the
TRFL
of
an Extremely
Noisy Source.
The only requirement on the signal source is that
it
have an auxiliary
output.
The awilliary output is down-converted and substitutes as the
local oscillator (LO) for the HP 8902A. With this setup, the same residual
FM, d r i f t , or instablilty present at
the signal source output is also present
on the LO input to the
HT
890214. This enables the IF Synchronous
detector in the HP 8902A to automatically track the noisy input signal.
Harmonic Mixing
In normal operation, the HP 8902A uses the fundamental mixing of
its internal local oscillator (LO) to make measurements to 1300 MHz.
You can extend the measurement range to 2.1 GHz
by
using
harmonic mixing of the internal LO. (Because harmonic mixing
produces higher conversion loss, measurement sensitivity begins to
degrade above 1300 MHz to -105 dBm at 2.1 GHz.) This is one
of three techniques available for extending the RF frequency range
of the
HP
8902A. The other two are also shown in this chapter.
1. Connect the
HP
8902A to the signal source and set the source level
to between
0
and
-20
dBm. Disregard Error 10 if it
is
displayed.
2.
Press
the Blue Shift key, the INSTR PRESET key, the
gold
S
key,
and the
TUNED
RF
LEVEL key.
3.
Key in 3.6 SPCL to select the narrow-band
455
kHz
IF filter.
4.
Press
the Blue
Shift
key and the DISABLE ERROR (RANGE
HOLD)
key to disable Error 01 if it remains in the display.
5.
Manually tune the
H P
8902A to a frequency equal to 0.30333 MHz
less than one third of the signal to b e measured. (For example,
to tune to a 2100 MHz signal, manually tune the HP 8902A to
699.6867
MHz: (2100/3)
-
0.30333
M W Z
=
699.6967 M H z . )
6.
Decrease the level of the input signal and perform the
TRFL
calibration.
Press the LOG/LIN key
if
you wish to toggle between Watts and dBm units.
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