External Timebase Reference

The external 10 MHz reference input BNC connector, both the shell and center pin, on the rear panel of the instrument is isolated up to ±42 Vpk from chassis. The shell of this BNC connector is isolated from the rest of the instrument. Internal circuitry will attempt to keep the isolated voltage to within ±42 Vpk to chassis. Attempts to float this input beyond ±42 Vpk from chassis may destroy the instrument and cause a hazard that could result in personal injury or death.

The external timebase reference provides rear panel connectors (10 MHz In and 10 MHz Out) and circuitry to allow synchronization between multiple instruments or to an external 10 MHz clock signal. You can also set the phase offset of the output waveform from the front panel or over the remote interface.

To align the phase of two instruments, use a dual-channel oscilloscope to compare the output signals:

  1. Connect the two instruments, with 10 MHz Out connected to 10 MHz In. Use the instrument with the more precise timebase as the 10 MHz reference output source.

    Instruments connected to lock timebases
  2. Connect instrument outputs to scope channel inputs:

    Connect instruments to scope
  3. Set the same frequency on both instruments. The scope should show the signals to be in sync with regard frequency, but not phase. (A square wave works well to show the phase difference.)
  4. For two-channel instruments, phase sync the two channels to each other. This also synchronizes each channel’s modulating waveforms to the carrier.

    Front panel:

    Channel keyParameters keyPhase softkey Sync Internal softkey

    SCPI: [SOURce[1|2]:]PHASe:SYNChronize
  5. Leaving the phase setting at its default (zero) on the first instrument, use Adjust Phase to adjust the phase of the second instrument to align the output signals:
Unaligned image Aligned image
Out of Phase Aligned

You can use Set 0 Phase to set a new zero-phase reference point with the two instruments now aligned.