5: Function Reference
F113 – J3 Input (Freq Meas)
Note: Frequency Measurement is an optional feature. If purchased at the same time as the
XL-GPS, it comes enabled on the system. To purchase this option after you have pur-
chased the XL-GPS, contact Symmetricom Sales. See “H: Sales and Customer
Assistance” on page204.
Use function F113 to configure J3 for a Frequency Measurement (Freq Meas) input, to
display Frequency Measurement information, or to disable J3 inputs.
F113 offers the following keypad settings:
• J3 Input Configuration: (FREQ MEAS, DISABLED) Displays “Disabled” if the
Frequency Measurement option has not been installed. Displays “Freq Meas” if it has.
• J3 Select Function: (DISPLAY FREQ MEAS, J3 INPUT CONFIG) Select to display
the Freq Meas information of to configure the Freq Meas input on J3.
• J3 Input Frequency: 1 MHz, 5 MHz, 10 MHz (Select the Freq Meas input frequency)
• J3 Input Impedance: 1kW, 50 W (Select the input impedance)
• Freq Meas Interval: 1 to 99999 seconds
The factory settings are 10 MHz, and 1kW.
Frequency Measurement (Freq Meas) Input
The Frequency Measurement (Freq Meas) option measures an external frequency applied
to the J3 input relative to the disciplined XL-GPS oscillator.
Operation: Measurements are displayed on the front panel display and on the command line
at the specified measurement interval. The front panel displays the measured frequency
offset (FREQ OFFSET) and a countdown (COUNT) to completion of the measurement
interval. The command line states the measurement interval (e.g.,“Interval is 1 seconds”) on
the first line, and then starts displaying each measurements; each one on a new line.
Limitations: Note that the accuracy of the frequency measurement is based on the accuracy
and stability of the disciplined XL-GPS oscillator over the measurement interval. Short
interval measurements of external very high stability oscillators (e.g., Cesium) tend to
measure the XL-GPS oscillator instead. Refer to “Time and Frequency Accuracy” on page4,
and to “Oscillators” on page18 for more information for the specifications of disciplined
oscillators (while locked to a GPS reference source).
Theory of Operation: Freq Meas uses a heterodyne phase error multiplier to achieve high
resolution at short sample periods. Using its internal disciplined frequency, the XL-GPS
records or timestamps the zero crossing of the J3 input frequency once per measurement
Page 138 of 221 .................................098-00116-000 Rev. A
To Next Page
Loading...
Need help?
General
