Selecting a Reference

Selecting a Reference
The E7495A/B supports three different types of frequency reference input for making frequency measurements. These are listed in the table below.
E7495A/B Reference Inputs

Reference
Type of reference provided
Notes

GPS Ref
Time and Frequency
Strongly recommended - provides accurate and network-independent measurements

Ext Ref
Frequency Only:
2.048 MHz, 10 MHz or 13 MHz
Recommended if no GPS signal is obtainable. Will only measure frequency and frequency error relative to BTS reference

Int Ref
Frequency Only:
Uses the test set's internal oscillator
Only recommended if no other reference signal is available. You must typically be within 750 Hz of the base station operating frequency when entering frequency or channel information in order for the test set to be able to lock to the Tx signal.

It is strongly recommended that you use the Global Positioning System (GPS) signal as the frequency reference for the W-CDMA and the W-CDMA (with HSDPA) Tx measurements because it provides an independent reference for measuring the operating frequency of the base station. A GPS antenna must be connected to the GPS input of the test set, and the antenna must have a clear view of the sky in order for the GPS to lock. If a GPS signal cannot be obtained, you can use the frequency reference provided by the base station to perform the measurement.
The E7495A/B test set supports all of the following frequency references and time references:

Frequency and Time - GPS (External antenna supplied)
Frequency and Time - External Even Second Pulse
Frequency only - Internal Reference
Frequency only - External 1.000 MHz (E7945B only)
Frequency only - External 2.048 MHz (E7945B only)
Frequency only - External 4.950 MHz (E7945B only)
Frequency only - External 10.000 MHz
Frequency only - External 13.000 MHz (E7945B only)
Frequency only - External 15.000 MHz (E7945B only)
Frequency only - External 19.6608 MHz
If you use the frequency reference provided by the base station, keep in mind that the frequency error metric will only be measuring the error relative to the base station reference signal, and not relative to absolute frequency and time. You will not be able to determine if the base station frequency is aligned with the other base stations in the network. Since the GPS provides an independent reference, the frequency error metric can be used to determine if the base station frequency is offset from the rest of the network.


Reference	Type of reference provided	Notes
GPS Ref	Time and Frequency	Strongly recommended - provides accurate and network-independent measurements
Ext Ref	Frequency Only: 2.048 MHz, 10 MHz or 13 MHz	Recommended if no GPS signal is obtainable. Will only measure frequency and frequency error relative to BTS reference
Int Ref	Frequency Only: Uses the test set's internal oscillator	Only recommended if no other reference signal is available. You must typically be within 750 Hz of the base station operating frequency when entering frequency or channel information in order for the test set to be able to lock to the Tx signal.