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The Spectrum Application
R&S
®
FPC
127
User Manual 1178.4130.02 ─ 07
R&S
FPC 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
FPC 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.
14.10.3
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.
If you enter a positive offset, the two temporary markers are placed below the active
reference point. If you enter a negative value (for example for notch filter measure-
ments), the two temporary markers are placed above the active reference point.
Measuring the signal bandwidth
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 "N dB Down" menu item.
The R&S
FPC shows two vertical lines in the diagram that represent the temporary
markers and measures the distance (bandwidth) between those two lines.
4. Select the "N dB <x>" menu item to select the distance between the temporary
markers.
Marker Functions