A Spectrogram is a three dimensional representation of frequency, time and power useful for identifying intermittent interference. Color is used to represent power levels.
Required Equipment
• An antenna that is appropriate for the frequency range to be measured
Required Setup
• Place the instrument in Interference Analyzer mode.
• Connect the antenna to the RF In test port.
Procedure
The following procedure demonstrates one example of an Interference Analyzer Spectrogram setup.
1. For the most effective spectrogram display, press the Amplitude main menu key, press the Reference Level submenu key and set the reference level such that the largest signal to be displayed will be near the top of the spectrum analyzer area of the screen. The reference value required can be determined by observing the color of the highest signal and changing the reference level to place that value near the top of the spectrum analyzer area.
2. Press the Scale submenu key and set the scale value to place the lowest signal near the bottom of the screen. In general, 4 dB/division or 5 dB/division will be good starting values.
3. Press the BW main menu key and set Auto RBW and Auto VBWOn, or set the applicable RBW and VBW values by pressing the RBW and VBW submenu keys.
4. Press the Measurements main menu key, then the Spectrogram submenu key to display the spectrogram. Press the Spectrogram key again to open the Spectrogram Menu.
5. Set the time between sweeps by pressing the Sweep Interval submenu key, or set the total time for a full spectrogram by pressing the Time Span submenu key.
6. To change the time between sweeps, press the Sweep Interval submenu key and use the rotary knob or keypad to set the time from 0 seconds to 60 seconds. Entering the time interval value causes the corresponding time span value to be automatically computed. The time span can be viewed or changed by pressing the Time Span submenu key and using the rotary knob or keypad to set the span. Changing the time span will automatically change the sweep interval.
Note
Setting a Sweep Interval value > 0 will change the detection method to Max Hold, so that any event within the time interval will be captured to the screen. This allows extended measurement times to be set.
7. To set the total time span for a complete display, press the Time Span submenu key and use the rotary knob or keypad to enter a time between 1 minute and 4,320 minutes (72 hours). Entering a time span value causes the corresponding sweep interval value to be automatically computed and shown when the Sweep Interval submenu key is pressed.
8. The instrument can be set so that spectrogram plots are automatically saved when the display is full. Press the Record submenu key to toggle saving On or Off.
9. The Time Cursor submenu key is used to turn on the horizontal time cursor. Use the up or down arrow key to move the cursor vertically through the spectrogram. The date and time that the measurement at the cursor position was taken is displayed at the top of the screen.
Note
When the Time Cursor is activated and is not on the zero trace position, the unit will automatically stop making measurements.
10. Press the Marker main menu key to place up to six markers on the signal and display the power and frequency at each marker position.
Note
Screen captured images are provided as examples. The image and measurement details shown on your instrument may differ from the examples in this Measurement Guide.
