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T A K I N G
M E A S U R E M E N T S
When your measurements are complete, again select Utilities
un-check this utility and resume normal operation.
3.7 Using the Measuring Receiver Utility
The measuring receiver utility takes measurements of AM and FM modulation and
relative signal level measurements. If you are familiar with other measuring receivers,
some of this information will be
redundant. In addition to modulation
measurements, the measuring receiver
also accurately measures relative power.
To use this, center the signal on the
graticule in the spectrum analyzer with a
span of 200 KHz or less, then select
Utilities->MEAS RCVR from the
menu. Note: The carrier frequency for
modulation measurements will be set to
the CENTER FREQ from the spectrum analyzer.
Enter the desired IF and audio settings, then click START to begin analysis.
3.7.1
Audio Analysis Controls
RF Carrier Freq: the frequency of the RF carrier.
⇒
IF Bandwidth: keep this at least 2.4x your peak FM modulation. Any
⇒
modulation outside this bandwidth will be rejected.
Audio Low Pass: This selects a digital low pass filter (windowed sinc) for
⇒
the demodulated audio, to reject high frequency audio noise. The filter
rejects audio modulation above the selected cutoff frequency, Fc.
Audio Band Pass: Narrow band audio filter (~160 Hz BW) to select a
⇒
single modulation frequency and reject all others.
The Synchronous / Average Level Detector is used to select between
⇒
two relative amplitude measurement modes.
o There are two gain ranges for RF level. If your amplitude
readings must span both ranges, you must take a stable power
level reading in the overlapping region (–45 to –65 dBm) to
properly calculate relative power. When the RF level is in this
20
Phase Noise Plot to
Figure 3: Measuring Receiver
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