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 page 204.
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:
1k
W
, 50
W
(Select the input impedance)
•
Freq Meas Interval: 1 to 99999 seconds
The factory settings are 10 MHz, and 1k
W
.
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 page 4
,
and to
“Oscillators” on page 18
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
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098-00116-000 Rev. A
Summary of Contents for XL-GPS
Page 1: ...XL GPS Time Frequency Receiver User Guide CD Part Number 098 00116 000 Rev A 5 May 2010 ...
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Page 220: ...I Certificate of Volatility See the following document 098 00116 000 Rev A Page 206 of 221 ...
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