US Patent 6,278,330 Copyright © SpectraDynamics, Inc. 2010
Mechanical Tuning
Mechanical frequency tuning is available to adjust the frequency of the internal
HROG-5 oscillator. Only fully qualified service personnel should perform this
procedure. Frequency adjustments should be made with the unit having been powered
on for at least 2 hours. Caution must be taken to avoid shorting or accidentally
touching a line voltage point.
1. To adjust the frequency of the oscillator, remove the top cover of the HROG-5.
The oscillator module is located at the right side of the instrument. The tuning
access for the 5 MHz oscillator is located on the top side of the oscillator
enclosure. A hermetic cover screw must be removed with a screwdriver to gain
access to the tuning screw. A small flat blade-tuning tool is needed to make the
adjustment.
2. Connect the external 5 MHz reference to the input labeled 5 MHz In. Make sure
that the reference signal level is between +10dBm and +15 dBm. Program the
HROG-5 to the nominal frequency offset that you want to use. For most
applications you may enter 0 Hz for the frequency offset.
3. Enter the PLL screen to view the RF power levels and control voltages. The
internal oscillator power level should be 12 1 dBm. The reference signal power
level should be between 10 dBm and 15 dBm. If the HROG-5 is phase locked to
the external reference the LOCK voltage will be greater than 0.2 V. Adjust the
mechanical tuning screw to achieve a lock condition. Continue adjusting the
mechanical tuning screw until the PLL voltage displayed is at 0 volts. At this
point the internal lock indicator LED should be on, the LOCK voltage should be
greater than 0.2 V and the PLL voltage should be at 0.0 0.2 V.
4. Replace all hermetic covers when done adjusting the frequency of the oscillators.
Replace the top cover of the HROG-5.
Note: The HROG-5 should be turned on for 2 hours prior to any mechanical
frequency adjustment.
