Rohde & Schwarz 1309.6000.08 - Measuring the Frequency

Using the Markers R&S FSH
1309.6275.12 4.30 E-2
Operating sequence:
 Press the MARKER key.
 Press the MARKER FUNCTION softkey.
 Using the cursor keys or the rotary knob, select the
NOISE menu item.
 Confirm the selection with the ENTER key or by
pressing the MARKER FUNCTION softkey again.
The R&S FSH now indicates the marker level in
dBm/Hz. If the delta marker is the active marker, it
displays the result in dBc/Hz. The reading is referred to
the main marker1.
Measuring the frequency
The FREQUENCY COUNT function is used to measure the frequency at the marker position. The
accuracy of the marker frequency readout is then no longer dependent on the pixel resolution of the
trace, but only on the accuracy of the internal reference frequency.
The R&S FSH calculates the marker frequency from the center frequency, the span and the frequency
of the trace pixel on which the marker is positioned. The trace has 631 pixels corresponding to
631 frequency coordinates. The frequency resolution is therefore relatively coarse – especially if a large
span is set. To circumvent this problem, the R&S FSH’s internal frequency counter can be used. When
frequency measurements are being made, the R&S FSH briefly stops the sweep at the marker position
and measures the frequency using the frequency counter. The resolution of the frequency counter is
0.1 Hz and so is considerably higher than the resolution that is obtained without the FREQUENCY
COUNT function. Even though the resolution is high, frequency counting is extremely fast due to a
special algorithm for the IQ baseband signal (approx. 30 ms at a resolution of 1 Hz). Basically, the
accuracy of the frequency readout depends only on the accuracy of the internal reference frequency
(TCXO).
The frequency counter only gives completely accurate readings for sine signals that are at least 20 dB
above the noise floor. If the S/N ratio is less, noise affects the results.
Operating sequence:
 Press the MARKER key.
 Press the MARKER FUNCTION softkey.
 Using the cursor keys or the rotary knob, select the
FREQUENCY COUNT menu item.
 Confirm the selection with the ENTER key or by
pressing the MARKER FUNCTION softkey again.
The R&S FSH now displays the counted marker
frequency with a resolution of 1 Hz. To indicate that the
FREQUENCY COUNT function is on, the marker
symbol changes from M1 to C1.