Specifications

Setting the Frequency R&S FSH
1145.5973.12 4.2 E-10
Setting the Frequency
The R&S FSH's frequency is set with the FREQ key. The frequency can be specified in terms of the
center frequency (center freq. = frequency at the center of the frequency axis in the measurement
diagram) or the start and stop frequency for a particular span.
It is best to enter the center frequency when a signal is to be measured at a known frequency. When
you are investigating signals, e.g. harmonics, that are within a particular frequency range, the best
option is entering a start and stop frequency to define the span.
Entering the center frequency
¾ Press the FREQ key.
The R&S FSH opens the frequency menu. Center frequency entry is always activated, so that the
frequency settings can be made with the minimum number of keystrokes. The current center frequency
is displayed in the value entry box. A new center frequency can be entered directly from the numeric
keypad. You can also use the rotary knob or the cursor keys.
¾ Enter the frequency you want from the numeric
keypad and terminate the frequency entry with the
appropriate unit (GHz, MHz, kHz or Hz).
The frequency you have entered now becomes the
new center frequency. The value entry box remains
open for any further entries.
¾ As an alternative, you can change the center
frequency with the rotary knob or the cursor keys
and terminate the entry with the ENTER key.
¾ You can clear the value entry box from the screen
by pressing the CANCEL key.
The smallest step for adjusting the center frequency with the rotary knob is a pixel, in other words, as
the trace comprises about 300 pixels, each step is equal to about 1/300 of the span. When you use the
cursor keys, a frequency step is equal to 10 % of the span (= 1 grid division). If you want to use a
different stepsize, you can define it with the CF STEPSIZE function (CF = center frequency).
When you are adjusting the center frequency, you may obtain a value that is outside the R&S FSH’s
maximum span. If this happens, the R&S FSH automatically reduces the span. It also outputs the
message "Span changed" to inform the user what has happened.
Setting a frequency offset
For measurements on frequency converters such as satellite downconverters, it is often convenient to
reference the results to the frequency prior to conversion. For this purpose, the R&S FSH offers a
frequency offset, which arithmetically shifts the center frequency to higher or lower frequencies; thus,
the R&S FSH displays the input frequency of the DUT.
Positive frequency offset is possible in the 10 Hz to 100 GHz range, in 10 Hz steps. The size of the
negative frequency offset permitted depends on the start frequency setting; the start frequency, taking
into account the frequency offset, is always ≥ 0 Hz.