Category: Knowledge Base DSA800 Series

This document provides step-by-step instructions on using the Rigol DSA-800 series of Spectrum Analysers to measure the characteristics of an RF Bandpass filter.
NOTE: The DSA must have a Tracking Generator to effectively perform the following test.

Normalize the trace (Optional)

Many elements in an RF signal path can have nonlinear characteristics. In many cases, these nonlinear effects on your base measurements can be minimized by normalizing the instrument.
1.    Connect tracking generator output to RF input using the same cabling that you will be using to test your device. Any element, like an adapter, used during normalization should also be used during device measurement as any changes to the RF signal path could effect the accuracy of the measurement.
2.    Enable the tracking generator by pressing the TG button > TG On
3.    Store the reference trace by pressing the TG button > Normalize > Stor Ref
4.    Enable normalization by pressing the TG button > Normalize > Normalize On

Measure the filter
1.    Connect the tracking generator output to the filter input using the appropriate cabling and connectors.
2.    Connect the filter output to the instrument RF input.

3.    Set the tracking generator amplitude by pressing the TG button and the TG Amplitude. You can use the keypad or wheel to enter the correct value.

NOTE: If your instrument is equipped with a Preamplifier,    you can enable it to lower the displayed noise floor    by pressing the following sequence:
Amplitude button > Down Arrow > RF Preamp On
4.    Enable the Tracking generator by pressing the TG button > RF Source ON You can see the small bump in the figure below.

Figure 1: Before Auto.

5.    You can use the Auto button to center and zoom on the waveform. You can also use the Freq and Span buttons to manually manipulate the displayed data.

Figure 2: After Auto.
6.    You can now enable the Marker function to measure the bandwidth and attenuation or passband characteristics of the filter.
7.    Press Marker Fctn > N dB BW and set  the function to the amplitude of interest. In this example, we are measuring the 3dB Bandwidth of our filter.

This document provides step-by-step instructions on using the Rigol DSA-800 series of Spectrum Analysers to measure the characteristics of an RF Amplifier. 

In addition to the DSA-800 Spectrum Analyser, you will need an RF Source, cabling, and adapters. 
Measure the amplifier
1.    Connect the RF generator output to the RF input of the instrument using the appropriate cabling and connectors. 
NOTE: If your instrument is equipped with a Preamplifier,    you can enable it to lower the displayed noise floor    by pressing the following sequence:
             
   Press AMP button > Down Arrow > RF Preamp On
 
        Figure 1: Preamplifier off
 
        Figure 2: Preamplifier on
2.    You can use the Auto button to center and zoom on the waveform. You can also use the Freq and Span buttons to manually manipulate the displayed data.
 

• Another option to center the waveform is to press Freq button > Peak → CF. This will automatically align the center of the display with the peak of the trace.
3.    Freeze the unamplified trace by pressing Trace > Trace Type > Freeze. You can use the Marker button to create a marker. This can be used to find the peak frequency and amplitude of the displayed waveform.
4.    Disable the RF Generator output.
5.    Disconnect RF generator from the instrument RF Input and connect it to the Amplifier input. 
6.    Connect the Amplifier output to the instrument RF Input.
7.    Enable the RF generator.
8.    Enable a second trace to visualize the amplified signal by pressing the Trace button > Select Trace 2.
9.    Set the trace type to Clear/Write by pressing Trace > Type > Clear/Write.
10.You can use the Auto button or manually center the trace using the Freq, Span, and Amp buttons.
11.Readjust the amplitude scale by pressing Amp > Auto
12.You can enable an additional marker for the new trace by pressing Marker > Select the marker you would like to use 
13. Now, select the trace you want to mark by pressing Marker > Marker Trace 
> select trace of interest
• Be sure Normal is selected to enable the marker
 

14.You can also enable a marker table by pressing Marker > Down Arrow > Mkr Table ON. This allows a convenient way to compare markers and values between traces.
 

15.    Alternately, you can use the Trace Math function to create a Trace difference on the screen. 
16.    Enable Trace Math by pressing Trace > Trace Math
17.    Set Function to A-B
18.    Set A = T1
19.    Set B = T2
20.    Set Operate > On
21.Set Amplitude by pressing AMPL > Auto
NOTE:  New trace appears. This represents Trace 1 – Trace 2. 
22. Set Marker to Math Trace by pressing Marker > select Marker 3 
23.Set Marker Trace to Math by pressing Marker > Marker Trace > Math
 

• You can then move the marker to the smoothest portion of Trace 3.

The Rigol DSA-815 Spectrum Analyser has a number of optional features that can be activated by obtaining an activation license.
Currently, the advanced measurement kit (DSA8-AMK), VSWR (DSA8-VSWR), and EMI Toolkit (DSA8-EMI) are available.
First, obtain the license key from your local Rigol representative.
The code is a 24 character code of alphanumerics.
Here is a sample:
XXX-XXX-XXX-XXX

1. Power on the instrument

2. Press System > Down Arrow 

      3. Press Install

     4. A textbox will appear
     5. Use the EDIT Keypad on the front panel to enter the alphanumeric code shown on the license.


NOTE: The “1” key will capitalize the letters (A/a).. The “+/-” key will toggle between Chinese (Shown as CN in the textbox), English(EN), and Number (1). Press the numeric character that contains the letter of interest. Multiple presses of the number key will scroll through the available characters. Press ENTER key to accept the letter.

6) Press the OK key after you have entered all of the characters. The instrument should indicate that the license option has been activated.

Many spectrum analysers, like the Rigol DSA800 series, have tracking generator options available. The tracking generator is an RF source that follows the frequency sweep settings of the spectrum analyser.  
For example, if you configure a spectrum analyser to sweep from 100 to 200MHz, and enable the tracking generator, the output of the generator would output a swept sine from 100 to 200MHz at the set amplitude. This sweeping function is useful when characterizing the frequency response of filters and amplifiers. 
 
Figure 1: Response of a filter to a swept RF input using a tracking  generator on a spectrum analyser. 
 
You can also use a tracking generator as a fixed frequency RF source by simply using the spectrum analyser in Zero Span Mode.  
In this note, we are going to configure a DSA815-TG in Zero Span mode to source a 50MHz Sine wave. 
1.    Set the center frequency to 50MHz by pressing FREQ > Center Frequency and set the value to 50MHz using the keypad or scroll wheel 
 
  
 
2.    Set the span to zero by pressing SPAN > select ZERO SPAN 
 
  
3.    Now, configure the tracking generator output by pressing TG > set the amplitude using TG LEVEL 
 
4.    Connect the RF output (TG output) of the spectrum analyser to the device under test 
 
5.    Enable the tracking generator output by pressing TG > ON 
 
Here is a scope capture of the 50MHz output of the TG: 

Communicating over LAN to the DSA series is straightforward. Here are some things to try if you are having difficulty:

1.    Make sure Ethernet cable is connected properly and that the switch/hubs in the network configuration are operating properly.
o    The green LED on the back of the DSA should display a solid illumination when the connection is made.
o    The yellow LED on the back of the DSA should blink when data is sent and received.
2.    The DSA defaults to communicate over USB. To configure the instrument for Ethernet, follow these steps:
o    Press System > I/O Setting > Remote I/O and toggle to LAN


•    Press System to Exit the menu
3.    Find LAN configuration and make sure it matches your instrument settings
•    Press System > I/O Setting > LAN




•    Record the IP Address, Subnet Mask, and Gateway
•    Open a web browser (Chrome, Internet Explorer, etc..) and type the IP address into the address bar at the top.


•    If everything is configured correctly, the DSA’s webpage will load

Starting at firmware revision 00.01.12, the DSA815 spectrum analyser can display the frequency scale in Log mode.
 
Press SPAN and set X Scale to Log 

To save a setup: 
1)    Insert USB stick into the USB port on the front panel 
 
NOTE: The format of the USB stick must be FAT32 
 
2)    Press STORAGE > Set BROWSER to DIR. You can press the button next to the Browser label to toggle the selection. 
  
 
 
3)    Use the scroll wheel to select Mobile Disk (E:) 
  

 
4)    Change File Type to Setup and press the back arrow to get back to the storage screen 
 
       
 
  
 
5)    Press Save, use the keypad to write a filename (I use numbers, they are faster), and press OK 

 

Spectrum analysers are extremely helpful tools for visualising signals in frequency space. This note will describe how to use settings to minimize error when performing peak measurements using a Rigol DSA Spectrum analyser.

Radio Frequency signals, especially continuous wave (CW) signals, have a finite frequency width.  Spectrum analysers, like the Rigol DSA series, use the 
Resolution Bandwidth Setting (RBW) to determine the bandwidth of the filter used analyse each resolution. For a fixed span, smaller RBW settings will equate to smaller frequency “steps” and finer frequency resolution measurement capabilities.  

If the bandwidth of the source is less than the RBW setting of the spectrum analyser, the resultant spectrum analyser trace will have a finite width and a shape very much like a Gaussian or Bell curve as shown in Figure 1.  

In Figures 1through 4, the input is a fixed 10MHz Sine wave. The only difference is the RBW setting  on the DSA. As you can see, the width of the trace decreases as the RBW decreases. This is because the width of the RF input is less than the RBW value. We are effectively viewing the width of the RBW filter.  

It’s also important to point out that the shape of the peak of the trace also changes. It goes from a “bubbled” shape with no real “peak” to a more pointed shape. Traces with “bubbled” shapes may have peak readings that vary because there is not a singular point that is has the highest amplitude.  
     
To achieve high accuracy peak measurements, you should use the smallest RBW setting that you can. If you have varying peak values, try lowering the RBW value and retest.  
 
  
Figure 1: 10MHz input, 300kHz span, RBW = 30kHz 
  

Figure 2: 10MHz input, 300kHz span, RBW = 10kHz 
 
    
Figure 3: 10MHz input, 300kHz span, RBW = 3kHz 
 
  
Figure 4: 10MHz input, 300kHz span, RBW = 1kHz

Microsoft Excel and Visual Basic for Applications (VBA) is a great way for engineers who need to analyse and archive data from their instrument to access the data without deep programming skills.

With this in mind, we have created VBA examples for some of our instruments including this one for Spectrum Analyzers including the DSA800 family.

Download the example file here

Users should also install UltraSigma to make certain all the necessary drivers exist on their system. 

Download the UltraSigma install pack here

Once UltraSigma is installed, the VBA macros can be used to communicate with the instrument. We have added a few buttons to make capturing a spectrum from the instrument simple.

Here is a look at the spreadsheet:



Download further instructions for getting started using this Excel file here

The Rigol DSA815 Spectrum Analyser has a built in Limit Line test that can be a convenient way to measure and compare spectral power against specific masks used for various signal types. 
One common test is NRSC Amplitude Modulation (AM) test. In this example, we are going to use the Pass/Fail mask to evaluate an AM Channel vs. limits set up by the National Radio Systems Committee (NRSC). 

Here is an excerpt from the FCC rule 73.44 

“The emissions of stations in the AM service shall be attenuated in accordance with the requirements specified in paragraph (b) of this section. Emissions shall be measured using properly operated and suitable swept-frequency RF spectrum analyser using a peak hold duration of 10 minutes, no video filtering, and a 300 Hz resolution bandwidth, except that a wider resolution bandwidth may be employed above 11.5 kHz to detect transient emissions. 
Alternatively, other specialized receivers or monitors with appropriate characteristics may be used to determine compliance with the provisions of this section, provided that any disputes over measurement accuracy are resolved in favour of measurements obtained by using a calibrated spectrum analyser adjusted as set forth above.” 

This provides the instrument settings we will use throughout this example.

1.    Set Center Frequency to match the channel you are monitoring. In this example, we are testing 1100kHz 
•    Press Freq > Center and adjust using the keypad or scroll wheel
 

2.    Set Span. In this case, we are testing AM NRSC which currently specifies 100kHz. 
•    Press Span > Span and adjust using the keypad or scroll wheel
 

3.    Set RBW and VBW.  This example requires 300Hz RBW and no video filter. 
We cannot disable VBW, but setting it larger than RBW effectively disables it.
•    Press BW/Det > RBW and adjust using the keypad or scroll wheel to 300Hz
•    While in the BW/Det menu, adjust the VBW to 3MHz. 

4.    Configure the analyser for a timed total. This test is specified for a total data collection time of 10 minutes. The easiest method to enable a timed test is to use the sweep and trigger controls of the instrument. 
•    Press Sweep > Mode > Single
•    Set Sweep Number > 600 ( at approximately 1.111s/sweep, this is a bit over 10 minutes)
 

5.    Set trace type to Max Hold
•    Press Trace > Trace Type > Max Hold

6.    Build Pass/Fail Limit line 
•    Build This can be performed manually or programmatically. See the Application Note titled “How do I create limit lines manually on the DSA815 series? or the Pass/Fail Limit builder software available for download on the DSA815 Product page located here www.rigolna.com. 

7.    Enable the Mask by pressing Trace/P/F > Pass/Fail > Switch On
•    Option: Pass/Fail Limit line press Trace/P/F > On > Setup
•    Option: Fail Stop Off/On to control the End Test On Failure Mode
•    Option: Beeper on Fail Off/On (P/F Menu 2/2)

8.    When ready to start the test, press Sweep/Trig > Single 
•    You can check the sweep count on the right hand side of the display
 

9.    After the test is complete, you can save a bitmap to an external USB memory. 
•    Insert USB stick into front USB port and wait for instrument to recognize the USB device.
•    If the device is not recognized, try another memory stick. USB drives with minimal files and folders will have a greater degree of success. Erase unneeded files and retry. 
•    Press the printer icon to save a BMP. 
NOTE: You can also save CSV data by pressing the Storage key.

10.    Clear traces and retest
•    Turn off mask – Press Trace/P/F > Off
•    Press Trace > Trace 1 > Type > Blank
•    Press Trace > Trace 1> Type > Max Hold
•    Press Trace/P/F > On
•    Press Start to begin test

General purpose spectrum analysers like the Rigol DSA series can be used to test the deviation of an FM signal. 

In this example, we are going to measure the FM deviation of a 10MHz FM signal with a DSA815. This is Rigol’s 1.5GHz spectrum analyser. 
NOTE: We are starting from Factory default settings. See the User’s Guide for the instrument you are using to learn more about restoring factory defaults. 
 
1.    Set the center frequency of the analyser to the carrier frequency of the FM signal.  
 
Press FREQ > Press Center Freg >  set Center Frequency using the scroll wheel or keypad 
 
2.    Set the Span to cover the expected frequency deviation of the input signal. 
 
Press SPAN > press Span >  set using the scroll wheel or keypad 
 
3.    Set the resolution bandwidth (RBW) to provide the resolution that is required for the test.  
 
Press BW/Det > Press RBW >  set using the scroll wheel or keypad 
 
4.    Enable a second trace type as Max Hold. We will leave trace 1 (yellow) as a 
Clear Write type. This will display the input values in “real time” and trace 2 (purple) will provide a histogram of the max values achieved for all scans. 
 
Press Trace/P/F > Select Trace 2 > Set Trace Type to Max Hold 
 
5.    Let the instrument scan for a period of time long enough to build a complete envelope of the modulated signals frequency deviation.  
 


The DSA815 has 10 divisions on the display. The span in this example is 20kHz. So, each division is 2kHz. In this example the FM deviation is approximately 2kHz.

The Rigol DSA815 Spectrum analyser features a zero span mode that can be helpful in observing modulated signals. In swept mode, the detector of the analyser is sweeping across a span of frequencies at a predefined rate. The display then shows the amplitude vs. frequency of that swept scan.  

In zero span mode, the detector is fixed at a selected center frequency with a bandwidth set by the resolution bandwidth (RBW) setting. The analyser then sweeps time. This effectively puts the analyser into a mode where the X-axis represents time and the Y-axis denotes amplitude. The display is then amplitude vs. time, much like an oscilloscope.  

The DSA-815 has a minimum sweep time of 20us in Zero span mode. In the following section, we show some of the outputs of the DSA with a modulated input. 

The source waveform is a 50MHz sine wave that was burst at various rates.  The burst period is measured from the leading edge of successive bursts.  

Hopefully this can help you to gauge whether the Zero Span Mode can help you with your modulation studies.   
  

Figure 1: Burst period 5us.  
 
  
Figure 2 : 50MHz Carrier sine wave zoom.  
 
  
Figure 3: 50MHz sine wave with a burst period of 10uS as captured by an Oscilloscope.  
 
  
Figure 4: 50MHz sine wave with a burst period of 10uS.  
      
There are 10 divisions on the display, so each division is 2us. In the case of the 10us burst, you can see that the peaks are separated by 5 divisions which equals  10us. So, the programmed sourced value and the measured values match.  
If we decrease the burst period to 5us, you can see that we increase the number of “peaks” displayed on the Spectrum Analyzer and the separation between the peaks is equivalent to the burst period. 
 
  
Figure 5: 50MHz sine wave with a burst period of 10uS.  
 
  
Figure 6: 50MHz sine wave with a burst period of 5uS.