Remote Spectrum Monitor™ MS27201A User Guide : Spectrum Monitor Measurements : Setting Frequency Parameters
 
Setting Frequency Parameters
Frequency-related parameters are set using the FREQ / SPAN Menu. The tuning frequency range can be entered in several different ways depending upon what makes the most sense, either for the user or for the measurement. The center frequency and span can be specified, the start and stop frequencies can be entered.
Entering Start and Stop Frequencies
The frequency settings are displayed along the bottom of the spectrum or spectrogram graph. These parameters can be accessed directly or via the FREQ SPAN menu.
1. Click FREQ SPAN on the main menu.
2. Click START FREQUENCY to open the start frequency parameter entry keypad.
3. Enter the desired start frequency. When entering a frequency with the keypad, available frequency units (GHz, MHz, kHz, and Hz) will be displayed along the left edge of the menu.
4. Click the appropriate frequency unit to terminate the entry or click ACCEPT to terminate the entry with the current frequency unit.
5. Click STOP FREQUENCY to open the stop frequency parameter entry keypad.
6. Enter the desired stop frequency. When entering a frequency with the keypad, available frequency units (GHz, MHz, kHz, and Hz) will be displayed along the left edge of the menu.
7. Click the appropriate frequency unit to terminate the entry or click ACCEPT to terminate the entry with the current frequency unit.
Note 
To quickly move the start or stop frequency value up or down, click the + or – slider controls to increment the frequency by the set FREQUENCY STEP. You can also drag the frequency using the slider.
The center frequency will be set to exactly the middle of the start and stop frequencies. The current settings are shown along the bottom of the spectrum or spectrogram graph (see Figure: GUI Overview (sample display elements)).
Entering a Center Frequency
1. Click FREQ SPAN on the main menu.
2. Click CENTER FREQUENCY to open the center frequency parameter entry keypad.
3. Enter the desired center frequency. When entering a frequency with the keypad, available frequency units (GHz, MHz, kHz, and Hz) will be displayed along the left edge of the menu.
4. Click the appropriate frequency unit to terminate the entry or click ACCEPT to terminate the entry with the current frequency unit.
Note 
To quickly move the center frequency value up or down, click the + or - slider controls to increment the center frequency by the set FREQUENCY STEP. You can also drag the center frequency using the slider or by dragging the trace directly.
Using Offset Frequency
A user‑defined frequency offset can be entered to adjust the frequency that is displayed on the instrument from the actual swept frequency. For example, if the DUT is an antenna system receiving signals in the 10 GHz range and offsetting the signals to the 1 GHz range, you can set a frequency offset in the spectrum monitor in order to display the actual received antenna frequency in the sweep window.
Both positive and negative offset values are allowed. Negative offsets can be useful for seeing differences from expected values. Enter a negative offset of the expected value, and the received antenna frequency should display in the 0 Hz range.
When enabled, the offset value is displayed at the left of the screen in the status panel (see Status Panel). To remove a frequency offset, open the FREQ SPAN menu and set FREQUENCY OFFSET to 0 Hz. You can also access this parameter directly from the left side status panel.
Note 
Offset frequency applies to start, stop, center, and marker frequencies.
Setting the Span
1. Click FREQ SPAN on the main menu.
2. Click SPAN to open the span frequency parameter entry keypad.
3. Enter the desired span frequency. When entering a frequency with the keypad, available frequency units (GHz, MHz, kHz, and Hz) will be displayed along the left edge of the menu.
4. Click the appropriate frequency unit to terminate the entry or click ACCEPT to terminate the entry with the current frequency unit.
5. To select full span, click the FULL SPAN. Selecting full span overrides any previously set start and stop frequencies.
Note 
To quickly move the span value up or down, click the + or - slider controls to increment the span in a 1:2:5 sequence. You can also drag the span using the slider or by pinching the trace in or out.
IF Output
IF output effectively allows the spectrum monitor to be used as a receiver front-end, converting the input signal at the spectrum monitor RF In connector to a signal centered at the IF output frequency. You can then process the IF signal in a way that meets your needs. That may mean using an A-to-D converter or some other signal processing method.
IF Output provides an IF signal of 325 MHz with FFT capture bandwidth ≤ 32 MHz and 300 MHz with FFT capture bandwidth = 100 MHz. The nominal RF output level is –4 dBm with a 10 MHz, –20 dBm input, and with 0 dB input attenuation and preamp off. The spectrum can be inverted in certain RF input bands. The IF output signal is present only when the spectrum monitor span is set to ZERO SPAN and the IF OUTPUT is toggled on (see FREQ / SPAN Menu (Zero Span)). You can select the IF output bandwidth of 750 kHz, 7.5 MHz, 14 MHz, 30 MHz, or 100 MHz using the IF OUTPUT Menu.
Note 
The selectable bandwidth values may differ among instrument models and options.
 
Selected IF Filter Bandwidth
IF Output Frequency
110 MHz
300 MHz
30 MHz
325 MHz
14 MHz
325 MHz
7.5 MHz
325 MHz
750 kHz
325 MHz
The normal IF BW uses analog bandpass filters in the normal RBW chain. By changing the RBW, different filter bandwidths are selected. While the IF bandwidth is influenced by the selection of RBW filters, the digital RBW filters themselves are not employed.
The spectrum monitor has several mixer bands. Depending on the operating frequency, the local oscillator may be above or below the input frequency. When the local oscillator frequency is below the input frequency, an increase in the input frequency results in an increase in the IF output frequency. When the local oscillator is above the input frequency, an increase in the input frequency moves it closer to the local oscillator frequency and the IF output frequency consequently decreases. The following table shows the bands and indicates where the LO frequency is, in relation to the RF frequency.
IF Inversion Bands
RF Band
Start Frequency (MHz)
Stop Frequency (MHz)
Spectrum Inversion
1
0
5350
Y
2
5350
7200
Y
3
7200
9200
Y
4
9200
11100
N
5
11100
13000
N
6
13000
16500
N
7
16500
20400
Y
8
20400
26950
Y
9
26950
33810
Y
10
33810
39900
Y
11
39900
47000
N
12
47000
54000
N
“Inverted” means that the IF is spectrally inverted from the input (as the input frequency goes higher, the IF goes lower).
“Not Inverted” means that the IF is not spectrally inverted (as the input frequency goes higher, the IF goes higher).
You need to take frequency inversion into account when processing the IF signal. Assuming that the IF has been processed to yield I and Q data, inversion is easily done by swapping I and Q.
A residual frequency offset of the IF may exist compared to the RF due to the resolution of the first and second local oscillators. This offset is usually on the order of several kHz, but may be up to 10 kHz or so. To determine the residual offset, you need a second spectrum monitor or a frequency counter.
1. Attach a signal source (or antenna) to the spectrum monitor and set the center frequency to the center of the signal being received.
2. Set Zero Span from the FREQ/SPAN menu, and then click IF OUTPUT to enable the IF output.
3. Attach a second spectrum monitor to the IF Out port and set the center frequency to 300 (or 325) MHz.
4. Set the span of the second spectrum monitor to 100 kHz with the resolution needed to be able to measure an offset that may be 25 kHz or less.
5. Measure the frequency of the IF signal to see how far the signal is offset from 300 (or 325) MHz.
FREQ / SPAN Menu
 
FREQ / SPAN Menu  
-
CENTER FREQUENCY
Sets the center frequency of the sweep range. The current span setting will remain constant or will be adjusted to accommodate the start and stop frequency range of the instrument. The center frequency can also be dragged on the display when gestures are not toggled off.
SPAN
Sets the sweep frequency range. The current center frequency will remain constant and the start and stop frequencies will be adjusted to accommodate the new range. Clicking the plus (+) or minus (–) control increments the span value in a 1:2:5 sequence. The span can also be changed by pinching the trace in or out when gestures are not toggled off.
FULL SPAN
Clicking this button sets the span to cover the entire tunable spectrum of the instrument.
LAST SPAN
Clicking this button returns the span to the previously set span value.
ZERO SPAN
Sets the monitor to zero span and enables the FREQ / SPAN Menu (Zero Span).
START FREQUENCY
Sets the start frequency of the sweep range. The center frequency and span will be adjusted to accommodate the new start and current stop frequencies. Clicking the plus (+) or minus (–) control moves the start frequency in steps defined by the FREQUENCY STEP value.
STOP FREQUENCY
Sets the stop frequency of the sweep range. The center frequency and span will be adjusted to accommodate the current start and new stop frequencies. Clicking the plus (+) or minus (–) control moves the start frequency in steps defined by the FREQUENCY STEP value (set lower in this menu).
FREQUENCY STEP
Sets the frequency step value used for the plus (+) or minus (–) control.
FREQUENCY OFFSET
The frequency offset value accounts for frequency conversions outside of the monitor. The offset frequency value is added to the start, stop, center, fixed marker, and normal marker frequencies. Clicking the plus (+) or minus (–) control moves the offset frequency in steps defined by the FREQUENCY STEP value.
GESTURES
Opens the GESTURES Menu.
FREQ / SPAN Menu (Zero Span)
 
FREQ / SPAN Menu  
-
 
CENTER FREQUENCY
Sets the center frequency of the sweep range. The current span setting will remain constant or will be adjusted to accommodate the start and stop frequency range of the instrument. The center frequency can also be dragged on the display when gestures are not toggled off.
SPAN
Sets the sweep frequency range. The current center frequency will remain constant and the start and stop frequencies will be adjusted to accommodate the new range. Clicking the plus (+) or minus (–) control increments the span value in a 1:2:5 sequence. The span can also be changed by pinching the trace in or out when gestures are not toggled off.
FULL SPAN
Clicking this button sets the span to cover the entire tunable spectrum of the instrument.
LAST SPAN
Clicking this button returns the span to the previously set span value.
ZERO SPAN
Sets the monitor to zero span and enables the FREQ / SPAN Menu (Zero Span).
FREQUENCY STEP
Sets the frequency step value used for the plus (+) or minus (–) control.
FREQUENCY OFFSET
The frequency offset value accounts for frequency conversions outside of the monitor. The offset frequency value is added to the start, stop, center, fixed marker, and normal marker frequencies. Clicking the plus (+) or minus (–) control moves the offset frequency in steps defined by the FREQUENCY STEP value.
IF OUTPUT
Opens the IF OUTPUT Menu. Requires Option 89.
GESTURES
Opens the GESTURES Menu
IF OUTPUT Menu
 
IF OUTPUT Menu  
-
 
IF OUTPUT
Toggles the top panel IF output on or off. When IF output is on, the IF OUTPUT BW button becomes active.
IF OUTPUT BW
When IF output is on, this button provides a list of IF output bandwidth settings.
GESTURES Menu
 
GESTURES Menu  
-
 
DRAG
Toggles the drag feature on or off. When toggled off, the center frequency will not change when dragging the spectrum display. This can be useful when dragging markers.
PINCH
Toggles the touchscreen pinch feature on or off. When toggled off, the span frequency will not change when pinching the spectrum display. This can be useful when dragging markers.
 
Operating the Touch Screen
Remote Spectrum Monitor uses common touch gestures to achieve a variety of operations. These include interactions on hot areas by pressing, double pressing (or tapping), dragging, and pinching.
Touch Screen Gestures
Single Press: Most controls require a single press or tap. Touch the screen briefly and then release.
Double Press: Some controls require a double press or tap. This action is similar to a double mouse click. If a second press is not detected in a certain time period, the action is dismissed or considered a single press.
Press and Drag: Some items can be dragged to a new location. This action is accomplished by pressing and holding the item lightly while dragging it to a new location, then releasing. You can drag items such as markers, limit line nodes, and the center frequency by dragging the trace to the left or right.
Pinch: Some items can be reduced or expanded. This action is accomplished by simultaneously pressing the item with two fingers and holding the item lightly when dragging the fingers in closer together or out farther apart, and then releasing. You can pinch items in or out, such as the frequency span by touching and holding the trace in two positions, and then dragging your fingers closer together to narrow the span or dragging your fingers farther apart to widen the span.
 
 
 
Note 
To use the Pinch functionality the user-supplied PC should be a touch screen enabled one, although not all touch screens support this capability.