Robotron Pty Ltd G3E Manuale Utente
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Appendix G – Frequency Calibration
The G303 receiver series features an excellent frequency accuracy and
stability for a receiver of its class. It is however possible to improve this
accuracy yet further, by individual calibration.
The receiver calibration is accomplished by inserting a reference frequency
parameter in the wrg3.ini file which resides in the Windows directory. The
reference frequency parameter consists of two lines of the following format:
[ClockCalibration]
receiver_serial_number=reference_frequency
The receiver serial number can be obtained from the About box in the G303
application. The reference frequency is the actual frequency of the internal
reference oscillator in Hz. This is nominally 20 MHz, i.e. 20000000 Hz.
Each receiver is factory calibrated, so a correction to the nominal 20 MHz
reference frequency already exists and is stored in the receiver's internal
memory. This correction can be overridden by the new parameter in the
wg3.ini file. To determine the true offset from a perfect tuning, firstly use
20000000 (i.e. the nominal reference frequency in Hz) as the new
reference_frequency parameter. Say your receiver serial number is
02L27011:
[ClockCalibration]
The receiver serial number can be obtained from the About box in the G303
application. The reference frequency is the actual frequency of the internal
reference oscillator in Hz. This is nominally 20 MHz, i.e. 20000000 Hz.
Each receiver is factory calibrated, so a correction to the nominal 20 MHz
reference frequency already exists and is stored in the receiver's internal
memory. This correction can be overridden by the new parameter in the
wg3.ini file. To determine the true offset from a perfect tuning, firstly use
20000000 (i.e. the nominal reference frequency in Hz) as the new
reference_frequency parameter. Say your receiver serial number is
02L27011:
[ClockCalibration]
02L27011=20000000
Open the existing wrg3.ini file, add the above two lines, then save the file
and start the G303 application. The frequency error will now be much worse
because this new parameter overrides the original factory calibration. Then
tune the receiver to a known frequency standard. A high-accuracy signal
generator can be used, or one of the WWV Time and Frequency Standard
stations. Observe the peak with the spectrum scope and listen to the beat
frequency in the CW mode with a minimum IF bandwidth. Typically, this will
be a negative number (for example, -652 Hz at 10 MHz).
Open the existing wrg3.ini file, add the above two lines, then save the file
and start the G303 application. The frequency error will now be much worse
because this new parameter overrides the original factory calibration. Then
tune the receiver to a known frequency standard. A high-accuracy signal
generator can be used, or one of the WWV Time and Frequency Standard
stations. Observe the peak with the spectrum scope and listen to the beat
frequency in the CW mode with a minimum IF bandwidth. Typically, this will
be a negative number (for example, -652 Hz at 10 MHz).
Then scale the frequency difference to 20 MHz. For example, if the
frequency difference is -652 Hz at 10 MHz, it will be -1304 Hz at the 20 MHz
reference frequency.
frequency difference is -652 Hz at 10 MHz, it will be -1304 Hz at the 20 MHz
reference frequency.