This application note looks at the details of an NADC PA test suite. It will address a search for a specified output condition, Gain, PAE and ACPR measurements. The main focus will be on the modulated measurements and ignores most of the standard CW tests that may be applicable as well.
1.) Measurement configuration:
Test Source Path Set Up
For this case we will use an Aux Source input to the combiner's AUX input shown above. We will need to control in the Test Plan:
a.) The Modulation Type, and Frequency
b.) The Initial Fixed Power Level
c.) The Routing Of the Aux Source and either SRC1 or SRC2 to the SRC1port into the testhead
On the optional RI Aux DMSG and the Src 12 combiner module the following buttons need to be added to the Global Defaults panel.
The Initial Source Power needs to be set for the given application to maximize the S/N ratio and have minimum waveform distortion. (see the RI Advanced applications training manual; PA section for more details.)
In this case the Mode Aux + SRC 2 combined to Aux is used to allow the Aux SRC and a CW Source to be used with out throwing a mechanical switch in the SRC 12 Module.
NOTE : Care must be taken that the during CW (SRC2) tests, the AUX SRC is attenuated by maximizing the Aux atten value. And vice-versa during modulated tests SRC 2 is turned off.
If at all possible do not change any settings of the AUX SRC during the test plan. That entails a GPIB command and most DMSG's are very slow at changing their settings. Set them up in the globals so they have time to execute their setup and stabilize.
2.) Finding a Target Output Power
In this panel the Aux Atten is swept and an RMS measurement of the entire tone is done. This must be done in a 4 MHz IF Bandwidth. The RMS detector allows TRUE RMS detection capability, necessary for broadband signals. See Effective Receiver Bandwidth
Note: For Gen II or earlier Testers with Recievers "E" or earlier, when measuring RMS signals with small (100kHz or less) bandwith, the receiver must be offset from the exact frequency. This is due to a center notch in the Wideband filter/RMS detector response. Typical offset values are 200 kHz.
It is critical that this section be UNOPTIMIZED. This insures that the power sweep goes from low to high. In a normal sweep with a regular source this would happen by default even in an optimized test plan. But in this case we are manipulating the Aux Atten. It is controlled with a DAC. The optimizer minimizes bit changes in the DAC, resulting in non- continuous sweeps.
Once this is done the Array can be searched for the target output value. See Set From Local Variable and Target Value
2.) Finding a Target Output Power ( continued )
In this case we find an Aux value to set for the Output measurements at 9.5 dBm
3.) Setting the Target Value and Making Measurements
Once the value is established It is set as a Set from LV in the Section Defaults: See Set from LV
Here are the section defaults for the measurement section.
Now the measurements are to be made. Sections involving ACPR measurements are one of the few times when The tests should be run un-optimized. In this case it is because the optimizer adds an unnecessary frequency move. It does this because it starts the section at the lowest frequency in the new section, not the last frequency in the last section.
By manually ordering the tests such that the tests at the center frequency come first followed by the +/- 30 kHz Measurements, we save a frequency move.
4,) Main Tone measurement:
This measurement is optional. It is there to verify that the sweep/set was successful. It can help if there are significant thermal effects in the sweep. It the part is robust another approach would be to use the target value itself and not do this measurement.
5.) Pin Measurement
For Gain and Efficiency the Pin value is needed. Notice this is made the same as the Pout measurement except the Testhead Parameter is the input wave A1
6.) Channel Power Measurement
Here the power in the main channel is measured. Note the 7kHz Bandwidth. This should not be exactly same as the Main Tone measurement as an NADC signal has significant energy outside the channel.
7.) Adjacent Channel Measurement:
For NADC the spec is Power in the adjacent channel 25 kHz BW - the power in the main channel in a 25 kHz BW. The Channels are 30 kHz spaced. Here we move the receiver 30 kHz and make a power measurement.
It is worth noting that since the NADC ACPR spec is in "Equivalent Bandwidth" ie. the main and alternate channels are measured the same, there is no bandwidth compensation needed
Here is an example testplan