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What does the system user alignment of my PSA EMI Measurement Receiver do?

The PSA / N9039A EMI Receiver has a couple of system level alignments that need to be run at regular intervals, or when the operating environment changes by a given amount (details can be found in the N9039A User's Guide).

Background

The purpose of the system user alignment is to compare the filtered signal path loss to the loss of the bypass signal path with both the internal preamp turned on and off, as well as to measure the input attenuation step error. With this information the system will calculate and apply the additional amplitude corrections needed. Because these are all relative measurements, and not compared across frequencies, the absolute level of the signal source is not crucial and the loss of the cable connecting the source to the preselector does not need to be accounted for.

Alignment Process

There are two different user alignments for the system, one for the Conducted signal path (9 kHz to 30 MHz)* and one for the Radiated signal path (30 MHz to 1 GHz). These can either be run individually or at the same time. These alignments are accessed on the PSA under the Mode Setup > Align RF Presel menu.

While the user alignment process is very complicated, the following description will give a higher level description of the alignment process.

When either of the alignment options are selected the system will:

  1. Verify communication with both the preselector and the alignment source
  2. Set the signal source to a power level of -30 dBm
  3. Measure the bypass path loss for the frequencies being measured for the selected path
  4. Measure the filtered path loss with the preamp off at the same frequencies for the selected path
  5. Measure the filtered path loss with the preamp on at the same frequencies for the selected path
  6. Measure the loss of the input attenuator at a single frequency for the selected path at all of the different attenuation levels
  7. Calculate the different signal path losses at each frequency measured and store the data

* While the Conducted signal path has a frequency range of 9 kHz to 30 MHz the system alignment for this signal path is only performed from 100 kHz to 30 MHz. It has been determined that the filter sections used below 100 kHz are very stable and a user activated system alignment for these filters is not required.