The Spectrum Application
FPC1000
104
User Manual 1178.4130.02 ─ 02
4. Select the "Noise" menu item again to turn off the noise measurement.
9.10.2 Frequency Counter
Access
: "Mkr" > "Marker Mode" > "Frequency Count"
The R&S
FPC1000 provides a frequency counter. The frequency counter accurately
measures the frequency at the position of marker 1 (M1).
When calculating the horizontal position of the marker, the R&S
FPC1000 includes the
current span, center frequency and the frequency of the pixel the marker is on. As the
trace only has a limited number of pixels, the marker position is usually just an approxi-
mation, especially if the span is very large.
With the frequency counter, however, you can get a more accurate result of the fre-
quency that the marker is positioned on. If the frequency counter is active, the
R&S
FPC1000 stops the measurement at the marker position for a short time and
measures the frequency using the internal reference frequency.
The accuracy of the results therefore depends only on the accuracy of the internal ref-
erence frequency. The frequency counter has a resolution of 0.1
Hz and therefore pro-
vides far more accurate results. Despite the accuracy, the measurement is still fast
(because of a special algorithm for the I/Q baseband signal).
The frequency counter only gives accurate results for sine signals that are at least
20
dB above the noise floor. If the S/N ratio is less, noise affects the results.
Measuring the frequency
1. Press the "Mkr" key to open the marker menu.
2. Select the "Marker Mode" menu item to open the marker function menu.
3. Select the "Frequency Count" menu item.
The R&S
FPC1000 displays the accurately measured frequency at the marker
position in the marker list.
4. Select the "Frequency Count" menu item again to turn off the frequency counter.
9.10.3 Signal Bandwidth Measurement
Access
: "Mkr" > "Marker Mode" > "N dB Down"
You can measure the signal bandwidth with the n dB down marker function.
The n dB down marker function uses the current value of marker 1 (M1) as the refer-
ence point. It activates two temporary markers on the signal, whose level is n dB below
the level of the reference point. One temporary marker is placed to the left and the
other to the right of the reference marker. The default setting for n is 3
dB, but it can be
changed.
Marker Functions
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