Keysight 8920 Internal SAT Signal Phase Delay

Here is one method for measuring the internal delay of the Keysight 8920A signal generator and RF analyzer. It involves the use of a dual-trace oscilloscope to measure the time delay. Once the time delay has been determined, it can be subtracted from the SAT phase measurement on a cellular phone. This method sets the Keysight 8920A s signal generator and RF Analyzer to the same frequency using the DUPLEX TEST screen. Both the RF analyzer input and the signal generator output are set to the RF IN/OUT connector on the 8920A s front panel.

Then the encoder is set to generate SAT the same way it is used on a voice channel. The encoder is set to send the SAT signal out to the front panel AUDIO OUT connector instead of the internal FM path. The audio output SAT signal is routed to the rear panel MODULATION INPUT and to "Trace A" of a dual-mode oscilloscope. This allows trace A of the oscilloscope to be used as the reference signal. The demodulated output from the 8920A s RF analyzer is then connected to the trace B input of the oscilloscope. This is the delayed signal after going through the 8920A s signal generator on RF analyzer. The time delay measured between trace A and trace B on the oscilloscope is the time delay of the 8920A.

On one 8920A tested at the factory, 118s delay was measured through the 8920A. This number may vary a small amount from one instrument to another.

The following assumptions were made:

A. The difference in delay between the internal FM path and the external FM path is nominal.

B. The difference in delay with the signal generator set to the same frequency as the RF analyzer instead of 45 MHz, different for a duplex cellular call, is nominal.

Following is the procedure for measuring the SAT delay of the 8920A:

1. Power on the 8920A.

2. Press the PRESET key, TX key, then the DUPLEX key.

3. On the DUPLEX TEST screen, make the following field changes:

Refer to the 8920A Field Setting Changes table.

All other fields on the DUPLEX TEST screen remain in the default conditions.

Make sure the Input Port is set to RF In and the Output Port is set to RF Out.

4. Go to the SIGNALING ENCODER (AF GENERATOR 2) screen.

5. Select the Mode field and choose: AMPS-TACS.

6. On the AMPS-TACS encoder screen, set the following fields:

Refer to the AMPS-TACS Field Settings table.

The "Status:"in the upper right corner of the encoder screen should be "Idle."

7. Go to the RF GENERATOR screen.

8. On the RF GENERATOR screen, set the following fields:

Field - Mod In To

Setting - FM (/Vpk), 2.00 kHz

9. Connect a BNC tee-adapter to the 8920A s AUDIO OUT connector on the front panel.

10. Connect a BNC cable from the AUDIO OUT tee connector on the 8920A s front panel to the MODULATION INPUT connector on the 8920A s rear panel.

11. The 8920A s display should be reading:

TX Freq Error: - Approx. 0.000 kHz

AF Freq: - Approx. 6.00000 kHz

FM Modulation: - Approx. 2.000 kHz

12. Connect a BNC cable from the AUDIO OUT tee-connector on the 8920A s front panel to the "Trace A" input on a dual-trace oscilloscope.

13. Connect a BNC cable from the AUDIO MONITOR OUT BNC connector on the 8920A s rear panel to the "Trace B" input on the dual-trace oscilloscope.

14. Adjust the dual-trace oscilloscope so that one cycle of trace A is displayed. Set the oscilloscope to trigger from the trace A input.

15. Measure the time difference from the peak of trace A to the peak of trace B. This time difference is the internal time delay of the 8920A s signal generator and RF analyzer.