HP 3048A Phase Noise - Typical Measurement Sequences

Below you will find the sequence of operations required to complete a typical phase noise measurement with the HP 3048A.

The measurement will be made on a HP 8657A Synthesized Signal Generator using the system 8662A as the reference, itself controlled by its EFC input.

The measurement will use one of the example parameter files delivered with the 3048 software, but it could be run from scratch following the same sequence and filling the various menus with your own parameters.

The detailed description of this test can also be found in the HP 3048A Operating Manual, starting page 92 of the PDF file.

HP 3048A Phase Noise - Checking the Loaded Measurement Parameters

From this point on, all the necessary parameters are loaded in the computer memory. The measurement could be started immediately, but each parameter can also be displayed separately, and modified if necessary. In other words, the following steps give the user the option to modify the measurement defined in the typical parameter file, to adapt it to a specific configuration of measurement.

The measurement parameters can be accessed or modified by the following options from the Main Menu:

HP 3048A Phase Noise - Measurement Sequences & Display

After the last step (shown above), pressing the computer's function key F1 will start the measurement routine. The various measurement sequences will be commented on the computer screen. The measurement time will depend on the measurement configuration. The following table shows approximate system run times for measuring various frequency offsets.

The following messages will appear on the display as the HP 3048A performs the calibration routines:

Determining the Presence of Beatnote: An initial check is made to verify that a beatnote is present within the system's detection range of 0.1 Hz to 40 MHz.

Verifying zero-beat: The frequency of the beatnote is measured to see if it is within 5% of the estimated Peak Tuning Range of the system. The system's Peak Tuning Range is the portion of the voltage-controlled-oscillator (VCO) source's tuning range being used for the measurement.

Zero beating sources: The center frequencies of the sources are now adjusted, if necessary, to position the beatnote within the 5% range. The adjustment is made with the tune voltage applied to the VCO source set at its nominal or center position.

Measuring the VCO Tuning Constant: The tuning sensitivity (Hz/V) of the VCO source is now precisely determined by measuring the beatnote frequency at four tune voltage settings across the tuning range of the VCO source. Linearity across the tuning range is also verified.

Measuring the Phase Detector Constant: The transfer characteristics (V/rad) of the HP 11848A's Phase Detector are now determined for the specific center frequency and power level of the sources being measured.

PLL suppression: The required correction data is created to compensate for the phase noise suppression which occurs within the bandwidth of the phase lock loop created for this measurement.

When the HP 3048A has completed the calibration procedures, it will lock the loop and begin its noise measurement. The Out of Lock light on the front panel of the HP 11848A turns off after the loop has been tested to verify phase lock.

If everything goes right, a Phase Noise Measurement Curve will be displayed step by step, starting from the upper decade down to the lower one. The picture below shows the actual result of the measurement configuration listed above, for the HP8657A used daily in our lab.

HP 3048A Phase Noise - Evaluating the Results

Looking at the measurement results, notice that the HP 3048A has measured and plotted both the random noise and deterministic (spurious) signals for the signal source under test. The HP 3048A differentiates the random noise (which has been normalized to a 1 Hz bandwidth) from the spurious (which are not normalized) by using a broken blue line to plot the spurs on the graph.

HP 3048A Phase Noise - Parameters Summary

When the measurement is completed, a summary of the parameters describing the configuration can be displayed or printed, using the following menu options:

HP 3048A Phase Noise - Spurious Listing

In the same way, a listing of the spurious appearing in the measurement curve can be displayed or printed, using the following menu options: