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22 Chapter 1
Making Basic Measurements
Making Better Frequency Measurements
Making Better Frequency Measurements
A built-in frequency counter increases the resolution and accuracy of
the frequency readout. When using this function, if the ratio of the
resolution bandwidth to the span is too small (less than 0.002), the
Marker Count: Widen Res BW message appears on the display. It
indicates that the resolution bandwidth is too narrow.
Better Frequency Measurement Example:
Increase the resolution and accuracy of the frequency readout on the
signal of interest.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz amplitude reference signal of the
analyzer as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the center frequency to 50 MHz by pressing FREQUENCY,
Center Freq, 50, MHz.
4. Set the span to 80 MHz by pressing SPAN, Span, 80, MHz.
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units,
dBm.
6. Set the resolution bandwidth to spectrum analyzer coupling pressing
BW/Avg, Resolution BW (SA).
7. Press Freq Count. (Note that Marker Count has On underlined turning
the frequency counter on.) The frequency and amplitude of the
marker and the word Marker will appear in the active function area
(this is not the counted result). The counted result appears in the
upper-right corner of the display.
8. Move the marker, with the front-panel knob, half-way down the skirt
of the signal response. Notice that the readout in the active
frequency function changes while the counted frequency result
(upper-right corner of display) does not. See Figure 1-13. To get an
accurate count, you do not need to place the marker at the exact
peak of the signal response.