Rohde & Schwarz FSH3 - Measuring the Frequency

Using the Markers R&S FSH3
Measuring the frequency
The FREQ 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 FSH3 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 301 pixels corresponding to
301 frequency coordinates. The frequency resolution is therefore relatively coarse – especially if a large
span is set. To circumvent this problem, the R&S FSH3’s internal frequency counter can be used. When
frequency measurements are being made, the R&S FSH3 briefly stops the sweep at the marker
position and measures the frequency using the frequency counter. The resolution of the frequency
counter is 1 Hz and so is considerably higher than the resolution that is obtained without the FREQ
COUNT function. Even though the resolution is high, frequency counting is extremely fast thanks 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:
¾ Press the MARKER key.
¾ Press the MARKER MODE softkey.
¾ Using the cursor keys or the rotary knob, select the
FREQ COUNT menu item.
¾ Confirm the selection with the ENTER key or by
pressing the MARKER MODE softkey again.
The R&S FSH3 now displays the counted marker
frequency with a resolution of 1 Hz. To indicate that the
FREQ COUNT function is on, Mark in the top left
corner of the screen changes to 'Count:'.
1145.5973.12 4.30 E-6